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deltas discussed as reservoir of hydrocarbon.
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DELTAS
Contents Introduction Classification of depositional environments Depositional environments Marginal-marine environments Deltaic system Controls on Delta Environment Sub-environments of delta Variation in delta morphology Processes in model delta Morphological units of delta Classification of Deltas Typical sequence Importance of delta Sedimentary structure in deltas Structural features of deltaic reservoir
Introduction To discuss deltas we should have great understanding
of depositional environment Depositional Environments Geomorphic setting in which a particular set of physical
chemical and biological processes operates to generate a certain kind of sedimentary deposit
Physical environment has ldquostaticrdquo and dynamic elements
1048708 Static basin geometry sediment composition water depth etc
1048708 Dynamic currents (wind water) precipitation climate
Chemical elements pH Eh salinity pCO2 etc Biological aspects activities of organisms (burrowing
skeletal particles etc) and their remains (eg peat)
Classification of Depositional Environments
Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments
Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore
Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)
Depositional Environments1048708 Objective Use sedimentary deposits to
interpret depositional environments
1048708 Physical biological chemical parameters of
an environment combine to produce a body
of sediment characterized by specific
textural structural and compositional properties
1048708 Distinctive bodies of sediments or
sedimentary rocks are facies
What happenshellip What we wanthellip
Marginal marine environment
The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms
It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the
system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions
Deltaic system
The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago
A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Contents Introduction Classification of depositional environments Depositional environments Marginal-marine environments Deltaic system Controls on Delta Environment Sub-environments of delta Variation in delta morphology Processes in model delta Morphological units of delta Classification of Deltas Typical sequence Importance of delta Sedimentary structure in deltas Structural features of deltaic reservoir
Introduction To discuss deltas we should have great understanding
of depositional environment Depositional Environments Geomorphic setting in which a particular set of physical
chemical and biological processes operates to generate a certain kind of sedimentary deposit
Physical environment has ldquostaticrdquo and dynamic elements
1048708 Static basin geometry sediment composition water depth etc
1048708 Dynamic currents (wind water) precipitation climate
Chemical elements pH Eh salinity pCO2 etc Biological aspects activities of organisms (burrowing
skeletal particles etc) and their remains (eg peat)
Classification of Depositional Environments
Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments
Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore
Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)
Depositional Environments1048708 Objective Use sedimentary deposits to
interpret depositional environments
1048708 Physical biological chemical parameters of
an environment combine to produce a body
of sediment characterized by specific
textural structural and compositional properties
1048708 Distinctive bodies of sediments or
sedimentary rocks are facies
What happenshellip What we wanthellip
Marginal marine environment
The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms
It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the
system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions
Deltaic system
The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago
A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Introduction To discuss deltas we should have great understanding
of depositional environment Depositional Environments Geomorphic setting in which a particular set of physical
chemical and biological processes operates to generate a certain kind of sedimentary deposit
Physical environment has ldquostaticrdquo and dynamic elements
1048708 Static basin geometry sediment composition water depth etc
1048708 Dynamic currents (wind water) precipitation climate
Chemical elements pH Eh salinity pCO2 etc Biological aspects activities of organisms (burrowing
skeletal particles etc) and their remains (eg peat)
Classification of Depositional Environments
Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments
Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore
Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)
Depositional Environments1048708 Objective Use sedimentary deposits to
interpret depositional environments
1048708 Physical biological chemical parameters of
an environment combine to produce a body
of sediment characterized by specific
textural structural and compositional properties
1048708 Distinctive bodies of sediments or
sedimentary rocks are facies
What happenshellip What we wanthellip
Marginal marine environment
The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms
It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the
system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions
Deltaic system
The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago
A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Chemical elements pH Eh salinity pCO2 etc Biological aspects activities of organisms (burrowing
skeletal particles etc) and their remains (eg peat)
Classification of Depositional Environments
Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments
Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore
Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)
Depositional Environments1048708 Objective Use sedimentary deposits to
interpret depositional environments
1048708 Physical biological chemical parameters of
an environment combine to produce a body
of sediment characterized by specific
textural structural and compositional properties
1048708 Distinctive bodies of sediments or
sedimentary rocks are facies
What happenshellip What we wanthellip
Marginal marine environment
The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms
It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the
system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions
Deltaic system
The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago
A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Classification of Depositional Environments
Nonmarine Environments Colluvial and Alluvial fans Fluvial environments Lacustrine environments Aeolian environments
Costal(marginal marine) Environments River mouth environments Regressive river mouthsDeltas Transgressive river mouthsEstuaries Open shoreline(beach) environments Foreshore backshore
Marine Environments Shallow marine environments Shoreface Inner and outer shelf Deep marine environments Continental slope Abyssal plain(basin floor)
Depositional Environments1048708 Objective Use sedimentary deposits to
interpret depositional environments
1048708 Physical biological chemical parameters of
an environment combine to produce a body
of sediment characterized by specific
textural structural and compositional properties
1048708 Distinctive bodies of sediments or
sedimentary rocks are facies
What happenshellip What we wanthellip
Marginal marine environment
The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms
It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the
system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions
Deltaic system
The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago
A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Depositional Environments1048708 Objective Use sedimentary deposits to
interpret depositional environments
1048708 Physical biological chemical parameters of
an environment combine to produce a body
of sediment characterized by specific
textural structural and compositional properties
1048708 Distinctive bodies of sediments or
sedimentary rocks are facies
What happenshellip What we wanthellip
Marginal marine environment
The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms
It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the
system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions
Deltaic system
The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago
A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
What happenshellip What we wanthellip
Marginal marine environment
The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms
It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the
system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions
Deltaic system
The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago
A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Marginal marine environment
The marginal-marine(transitional) setting lies along the boundary between the continental and the marine depositional realms
It is a narrow zone dominated by Riverine Wave Tidal processes Salinities may range in different parts of the
system from fresh water through brackish water to supersaline depending upon the river discharge and climatic conditions
Deltaic system
The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago
A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Deltaic system
The term ldquodeltardquo the Greek character was used to describe the mouth of Nile by Herodotus nearly 2500 years ago
A modern definition cites delta as ldquothe sub aerial and submerged contiguous sediment mass deposited in a body of water(ocean or lake) primarily by the action of a riverrdquo(Moore and Asquith1971p2563)
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Deltas seldom form on active subducting continental margins because there is no stable shallow shelf on which sediments can accumulate
Shape of Delta The shape of a delta is not always the triangle that
suggested the name to Herodotus Delta shape is influenced by
a) Sediment input
b) Wave energy
c) Tidal energy
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Controls on delta environment
Factors affecting delta regime morphology and facies (Elliot 1978a)
Magnitude of fluvial discharge
Delta morphology and sedimentary facies
Delta regime
Magnitude of wave and tidal currents
Climate tectonics subsidence sediment supply topography
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Subenvironments of Delta Deltas are influenced by a complex combination
of fluvial and marine processes Each delta has more than a dozen distinct
environments of deposition These environments can be grouped into three
broad divisions
1 The delta plain with the meandering flood plains Swamps and beach complex
2 The steeper delta front
3 The broadly sloping prodelta which grades into the open shelf
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Variations in delta morphology
The combinations of factors that control delta morphologies give rise to a wide spectrum of possible delta characteristics
Two main factors are the most important in determining the morphology of deltas
1) Effect of grain size
2) Depth of water in delta are going to deposit
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
(a) a high proportion of suspended load results in a relatively small mouth bar deposited from bedload and extensive delta-front and prodelta deposits
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
(b) a higher proportion of bedload results in a delta with a higher proportion of mouth bar gravels and sands
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
(a) A delta prograding into shallow water will spread out as the sediment is redistributed by shallow-water processes to form extensive mouth-bar and delta-front facies
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
(b) In deeper water the mouth bar is restricted to an area close to the river mouth and much of the sediment is deposited by mass-flow processes in deeper water
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Processes in a model delta Reduced to its simplest elements a delta forms
due to ldquounique hydrodynamic interactionrdquo between river water and seawater
There is sharp contrast in water density due to salinity As a result river water forms a plane jet that spreads out and forms a layer over the seawater
Current velocity diminishes radially from the jet mouth depositing sediments whose settling velocities allow grain size to diminish radially from the jet mouth
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Development of the delta through time by progradation (A B D) and distributary switching (C) (From Davis 1983)
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Levees Ridges on either side of the distributary channels
are termed ldquoleveesrdquo The sand carried in the stream is deposited along
the sides of the jet in the subaqueous levees where friction and mixing slow the flow
Distributary channels It is channel that branches off and flow away from
a main channel or stream Common feature of delta
Distributary channel sands are abundantly
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
I Cross-bedded with plenty of ripple cross-lamination
II Scour-and-fill structures
III Discontinuous clay lenses
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Distributary mouth bars Further offshore where friction and spreading
begins to slow the jet sediments is dropped in the distributary mouth bars
The distributary mouth bar sands are even more complexly cross stratified because of the complex current system that pass over them
Wood debris and other organic matter carried down the river during floods end up in the distributary mouth bars
Between the distributaries on the delta plain are wide shallow ldquointer-distributary baysrdquo and ldquomarshesrdquo like the flood plains of the meandering river Much of inter-distributary sequence is built of sand sheets from ldquocrevasse splaysrdquo deposited
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Morphological units of deltas Three main morphological units appear Delta platformplain The delta platform is the sub-horizontal surface
nearest the jet mouth It is basically composed of sand and traversed by the distributary channel and its flanking levees
Delta slopefront The delta platform grades away from the source
into delta slope on which finer sands and silts come to rest Commonly burrowed sand coarsing upward and have good porosity and permeability
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Pro-delta Delta slope in turn passes down into the delta slope
on which finer silts and clays settle out of suspensionpro-delta deposits rest unconformable on marine shelf deposits which may include nonclastic components such as algal reefs
Classically these three elements termed as 1-bottomset 2-foreset 3-topset respectively
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Classification of delta Deltas can be classified in several ways
(Nemec 1990) however classification on the basis of delta-front regime (Galloway 1975) appears to be favored by most geologists
Deltas are classified thus as
1) Fluvial-dominated delta
2) Tide-dominated delta
3) Wave-dominated delta
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
The forms of modern deltas (a) the Nile delta the lsquooriginalrsquo delta (b) the Mississippi delta a river-dominated delta (c) the Rhone delta a wave-dominated delta (d) the Ganges delta a tide-dominated delta
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Fluvial-dominated delta A fluvial or river dominated delta has a large
volume of sediment and tends to be ldquolobaterdquo when there is a moderate sediment supply and ldquoelongaterdquo when the sediment supply is large
If the sediment supply cannot keep up with the erosive powers of tides than the delta tends to be very small
It occur where the tidal range is very low and the tidal current action is very weak
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
ExampleMississippi delta It is created when very large amounts of sediment
are carried into relatively quiet water Partly because dredging has kept the major
distributary channels (locally called ldquopassesrdquo) fixed in position for many decades the Mississippirsquos distributaries have built long fingers of sediment out into the sea
The resulting shape has been termed a ldquobirdfootrdquo delta Because of the dominance of stream sedimentation that forms the fingerlike distributaries birdfoot deltas like the Mississippirsquos are also referred to as stream-dominated deltas
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Stream-dominated delta
Aster satellite photo of the Mississippi River delta taken in 2001
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Tide-dominated delta A tide dominated delta has many linear channels
parallel to the tidal flow and perpendicular to the shore
It occur in regions where wave action is limited and tidal ranges are generally in excess of 4 m generating strong tidal currents -- have a major effect on mixing of river water and seawater and on sediment redistribution
These deltas form along a coast that is dominated by strong tides and the sediment is reshaped into tidal bars that are aligned parallel to a tidal current
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Example
The Ganges-Brahmaputra
Delta in Bangladesh is a good example of a tide-dominated delta
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Wave-dominated delta A wave dominated delta is smoothly arcuate the
wave action reworks the sediments and make such deltas much sandier than other types of deltas
It occur where wave energy is high out-flowing freshwater behaves as a countercurrent slowing down oncoming wave crests and causing waves to break in deeper water than normal
this leads to vigorous mixing rapid deceleration of the freshwater flow and sediment deposition wave action reworks the deposited sediments to form sand bars and beaches creating a straight shoreline with only a small protuberance at the distributary mouth
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
ExampleThe Nile Delta
It is a wave-dominated delta that contains barrier islands along its ocean-ward side
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
mixed-process deltas The examples discussed above illustrate some
differences in characteristics of modern deltas that are shaped by processes that are predominantly fluvial tidal or wave related
Many deltas have characteristics that are transitional between these end members types
Example The Copper River delta in the Gulf of Alaska
provide an example of a delta that is strongly influenced by tides but also experiences high wave power(Galloway 1976)
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
The Copper River Delta Gulf of Alaska
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
General delta patterns A well-developed delta provides the whole gamut
of clastic sediment types from carbonaceous mudstones to conglomerates
The proportions of the sediments types are controlled chiefly by the interaction of fluvial agency supplying the material and the marine agency receiving it This interaction leads to four general deltas patterns
I High-destructive deltas
II High-constructive deltas of birdfoot type
III High-constructive deltas of lobate type
IV Fan deltas
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Typical sequence
The classical stratigraphic profile of deltaic deposits shows a coarsening upward sequence from the delta slope muds and silts to the distributary mouth bar sands
This is opposite to the fining upward sequence found in most meandering fluvial system
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Why deltas are so important Ancient deltaic deposits are extremely important
economically Due to variety of environments in the deltas it
makes more important for a reservoir geologists Many oil and gas-fields are in sedimentary
deposits associated with deltas Located near the boundaries between marine
deposits which include source sediments and non-marine deposits which represent the supply zone for reservoir rocks deltas are ideally situated for the maximum interplay between source and reservoir facies
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
They hosts most of the worldrsquos coal and many major petroleum provinces
The deltaic process is a way of deposition lobes of sand (potential reservoir) into envelopes of organic-rich marine muds (potential source beds)
Deltaic environments deposit many potential stratigraphic traps including mouth bars barrier bars and channels
Rapid deposition often leads to over-pressuring This may generate diapiric traps and roll-over anticlines
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Sedimentary structures and fossils
Numerous types of sedimentary structures such as
1 Cross bedding
2 Ripple marks
3 Bioturbation structures
4 Slump structure and
5 Mud diapirs occur in deltaic deposits
A ldquoMud diapirrdquo is a dome or fold in sediments that is formed by the plastic deformation of mud underlying sand or other sediments Diapirs called mudlumps frequently emerge in distributary mouth bar deposits
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Structural features in deltaic reservoir
Structural features result from deformation of sediments and rocks includes faults folds tilting(dip) and fractures
Structural features can broadly divided into two classes based on the timing of the deformation
Syndepositional deformation features Syndepositional deformational processes which
includes
a Slumping
b Mud diapirism
c Growth faulting are common in lower delta plain environments and operate during delta formation
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Post-depositional deformation Post-depositional deformational features includes
a Folding
b Tilting faulting fracturing This is due to tectonic forces and consequent
movement of earthrsquos crust
Significances Structural features can modify the sandstone body
geometry These features are important in the migration
accumulation and trapping of petroleum
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Migration of hydrocarbons from the source rock enhanced by
Faulting and Fracturing These accumulation or trapping of oil is caused by
permeability barriers which prevent further migration of the petroleum
When the permeability barriers is a structural feature the reservoir is considered structural traps
Fracture and faults are important on an inter-well scale where they control the movement of both injected and naturally occurring reservoir fluids and may significantly affect the production of hydrocarbons
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Examples in Pakistan
Samber Formation is source rock of deltaic environment
Goru Formation is a reservoir rock of deltaic environment
Its upper part acts as a seal rock
Thank You
Thank You