Lecture 14_Petroleum Geology_Sokari Braide (2)

Study of sedimentary rocks Dr. Braide

Mechanisms of plate formation Dr. Braide

Basin classification Dr. BraideBasins and sequence stratigraphy Dr. Braide

Basic Petrophysical Concepts Dr. Opuwari

Well logging Dr. Braide

Sokari BraideSokari Braide

APG 711 APG 711 -- Course ContentCourse Content

PETROLEUM GEOLOGYPETROLEUM GEOLOGY

Well logging Dr. BraideCore analysis Dr. OpuwariCalibration of Log/core Dr. OpuwariOverburden correction Dr. Opuwari

GaryPercival LimitedGaryPercival LimitedGaryPercival LimitedGaryPercival Limited©CopyrightUniversity University of the of the of the of the of the of the of the of the Western CapeWestern Cape

Department of Earth SciencesSlide 1

Lecture 14

Sokari BraideSokari BraideSequence StratigraphySequence Stratigraphy



What is Sequence StratigraphyWhat is Sequence Stratigraphy

Sokari BraideSokari BraideSequence StratigraphySequence Stratigraphy



Sokari Braide

Sequence Stratigraphy Sequence Stratigraphy Sequence Stratigraphy Sequence Stratigraphy

A framework of genetically related

stratigraphic facies geometries and their

bounding surfaces used to determine

depositional setting

Sequence StratigraphySequence Stratigraphy


Department of Earth Sciences

Establish Setting

Slide 4

Sequence StratigraphySequence Stratigraphy(a) Passive margin

Sedimentary sequences form on the edges of continents when sediment influx is modified by fluctuations in sea level.

Sokari BraidePetroleum Geology 1Petroleum Geology 1

Schematic profiles of three types of continental margins. (a) Passive margin. (b) Active margin of the

Marianas type. (c) Active margin of the Andean type.

(b) Active margin of the Marianas type (c) Active margin of the Andean type




Sequence StratigraphySequence StratigraphySedimentary sequences form on the edges of continents when sediment influx is modified by fluctuations in sea level.

(a) How a turbidity current forms in the oceans. These currents can erode and transport large quantities of sand down the continental slope. Submarine canyons are deep valleys eroded into the continental shelf and slope by turbidity currents.



(b) Sandfall at the head of a submarine canyon at the edge of the continental shelf. These falls generate sandy flows, such as turbidity currents, that lay down fans of sandy sediments at the foot of the continental slope.

Slide 6

Sokari BraideSequence StratigraphySequence Stratigraphy

East Coulee Delta (approximately 1 m wide; modified from Posamentier et al., 1992a; demonstrating the applicability of sequence stratig raphic concepts at virtually any scale. In this example, the highstan d systems tract was left behind, and it was subsequently incised as a result of the fall in the local (pond) base level during the progradation of the lower elevation lows tand delta.





Until a few decades ago, geologists had to rely on rock outcrops or by drilling to map stratigraphic successions.

Technological advancement in seismology now allow u s to see below Earth’s surface without actually going there.

From seismic data, we can construct three-dimension al images of deeply buried structures.

Basic geologic unit observed bounded by unconformit ies is a sedimentary sequence.

This type of detailed geologic mapping is called sequence stratigraphy.





In this example, sediment is laid down in a delta. As the sediment builds up the seafloor to sea level, the delta advances toward the sea.When the sea level falls, the deltaic deposits are exposed to erosion.The shoreline shifts inland when the sea level rises again, and a new deltaic sequence begins to cover the old one, creating an unconformity.





Over millions of years, this cycle may be repeated many times, producing a complex set of sedimentary sequences.Because sea level fluctuations are worldwide, we can match sedimentary sequences of the same age overwide areas (see next slide ).



Eustatic CyclesEustatic Cycles Sokari Braide



Sokari Braide

Walther’s LawWalther’s LawFig. 7

Facies AnalysisFacies Analysis



Walther’s Law: the principle that connects the late ral and vertical shifts of facies within a sequence (i.e., a relatively conformable successi on of genetically related strata).

Slide 12

Sokari BraideFig. 7

Sequence stratigraphic vs. lithostratigraphic frameworks, starting from th e same set of facies data.

Walther’s LawWalther’s Law




1. The reconstruction of paleodepositional environm ents via facies analysis is an important pre-requisite for sequence stratigraphic interpretations. The nature of stratigraphic contacts (scoured, conformable) also needs to be assessed via sedimentological analysis .

Slide 13

Sokari Braide


Walther’s LawWalther’s LawFig. 7 continued




2. The sequence stratigraphic framework is constructed by correlating the key sequence stratigraphic surfaces . All sequence stratigraphic surfaces shown on the cross section are good chronostratigraphic markers (low diachroneity), wit h the exception of the transgressive wave -ravinement surface which is highly diachronous.

Slide 14

Sokari Braide


Walther’s LawWalther’s LawFig. 7 continued




3. Sequence stratigraphic cross section, showing key surfaces, within-trend f acies contacts, and paleodepositional environments. Within-trend facies contacts, marking lateral changes of facies, are placed on the cross-section after the sequence stratigraphic framework is const ructed. Facies codes : A—meandering system; B—braided system; C—estuary-mouth complex; D—c entral estuary; E—delta plain; F—upper delta front; G—lower delta fron t—prodelta.

Slide 15

Sokari BraideFig. 7 continued


Walther’s LawWalther’s Law




4. Lithostratigraphic cross-section. Three main lit hostratigraphic units (e.g., formations) may be defined: A—a sandstone-dominated unit; B and C – m udstone-dominated units, with silty and sandy interbeds. Formations B and C are separat ed by Formation A. Additional lithostratigraphic units (e.g., members—subdivisions of units A, B, C) may be defined as a function of variations in lithology and colour.

Slide 16

Sokari BraideFacies AnalysisFacies Analysis

MAIN FEATURES of sedimentary rocks that can be observed directly in the field are:

�Bedding – including thickness, geometry, nature of bed boundaries, dip and strike of the beds, and way-up criteria.

�Sedimentary structures – including erosional, depositional, deformational, biogenic and chemogenic.

�Textures – including grain size, sorting, grading, porosity-

SummarySummary



�Textures – including grain size, sorting, grading, porosity-permeability, grain morphology, grain surface texture, and sediment fabric.

�Composition – including clast types, mineralogy and fossil content.�Colour – distinguishing between weathered and fresh surfaces.

Collectively, these attributes are used to define a sediment facies or lithofacies (lithotype) or, simply, facies .

Slide 17

Sokari BraideFacies AnalysisFacies Analysis

A sediment facies is defined as (or sedimentary rock) that displays distinctive physical, chemical and / or biological characteristics (of the sort listed above) that make it readily distinguish ed from the associated facies.

These are the primary building blocks of all sedime ntological studies.

They are used as a means of recording data, for describing sediment

SummarySummary



They are used as a means of recording data, for describing sediment outcrops and successions and, subsequently, for making interpretations concerning, for example, depositional processes, environmental conditions or economic significance.

In ancient deposits the vertical sequence of facies is generally much easier to observe than the lateral sequence, a circumstance that is the exact opposite of the situation in modern sediments.

Slide 18

Sokari BraideFacies AnalysisFacies AnalysisIn attempting to reconstruct environments from facies, therefore, geologists have often been guided by Johannes Walter’s Law of Succession of Facies = “facies sequences observed vertically are also found laterally”

SummarySummary



Cross-section of a sedimentary basin to show the relationship

between facies, environment and time.

Highly simplified application of Walther’s

Law of Succession of Facies

Sedimentary facies is defined as any areally restricted part of a designated stratigraphic unit which exhibits characters significantly different from those of other parts of the unit.

Slide 19

Sokari Braide

Facies : the total textural, compositional and structural characteristics of a sedimentary deposit resulting from accumulation and modification in a particular setting.

Sedimentary FaciesSedimentary Facies



Sokari Braide

Facies : the total textural, compositional and structuraltotal textural, compositional and structuralcharacteristics of a sedimentary deposit resulting from accumulation and modification in a particular setting.




•• grain size, sorting, roundinggrain size, sorting, rounding

•• lithologylithology

•• sedimentary structuressedimentary structures

•• bedding typebedding type

•• fossil assemblagesfossil assemblages

Slide 21

Sokari Braide

Facies: the total textural, compositional and structural

characteristics of a sedimentary deposit resulting from

accumulation and modification in a particular setting.

EX: well-sorted, moderately rounded, trough cross-stratified, horizontally

burrowed & normally graded arkosic coarse sandstone




Sokari Braide

Lithofacies & Lithofacies CodesLithofacies & Lithofacies Codes

Sedimentary facies often get reduced to lithofacieswhich detail grain-size, composition, and dominant sedimentary structures only

� EX: planar cross-stratified gravel, inversely graded massive

Sedimentary Facies Sedimentary Facies



� EX: planar cross-stratified gravel, inversely graded massive sandstone

This has led to lithofacies codes (after Miall, 1978).

� EX: Gmm, St, Fsl

Slide 23

Sokari BraideSedimentary Facies Sedimentary Facies


Facies associations : collection of multiple facies (often in a vertical cycle) resulting from genetically related accumulation and modification.



accumulation and modification.

� EX: lenticular bedded stratified pebble conglomerate with subordinate planar cross-stratified sandstone

� OR: fluvial channel lithofacies assemblage

Slide 24

Sokari Braide


Facies associations : collection of multiple facies (often in a vertical cycle) resulting from genetically related

Sedimentary Facies Sedimentary Facies



in a vertical cycle) resulting from genetically related accumulation and modification.

Facies successions : collection of multiple stacked vertically facies associations resulting from genetically related accumulation and modification.

Slide 25

Sokari BraideFacies SuccessionsFacies Successions



Sokari Braide

Relationship between:Relationship between:

FaciesFacies

SedimentarySedimentary

GeologyGeology

Depositional SystemsDepositional Systems



FaciesFaciesArchitectural elementsArchitectural elementsDepositional settingsDepositional settingsSystemsSystemsSystems tractsSystems tracts

Scheme used to characterize Scheme used to characterize each depositional each depositional system.system.

Slide 27

Sokari Braide

marine � ocean, sea

terrestrial land

Types of Depositional SystemsTypes of Depositional Systems




terrestrial � land

transitional � part land, part ocean

Slide 28

Sokari Braide

Shallow/nearshore� Tide-dominated� Wave-dominated� Reef

Marine Depositional SystemsMarine Depositional Systems

Shelf/platformShelf/platform




� ReefShelf/platform

� Carbonate� Clastic

Deep marine� Deep sea fans� Pelagic

Slide 29

Sokari Braide

Terrestrial Depositional SystemsTerrestrial Depositional Systems

Fluvial-alluvial fanGlacial

FluvialFluvial--Alluvial FanAlluvial Fan




GlacialAeolianLacustrinePlaya

AeolianAeolian

Slide 30

Sokari Braide

Transitional Depositional SystemsTransitional Depositional Systems

DeltasEstuaries

DeltaDelta




Estuaries

Slide 31

Sokari Braide

Clastic Depositional SystemsClastic Depositional SystemsClastic Depositional SystemsClastic Depositional Systems




Sokari Braide





Sokari Braide





Sokari Braide





Clastic Depositional Simulation

by

University University of the of the of the of the of the of the of the of the Western CapeWestern Cape


by

Professor Christopher G. St. C. Kendal

University of South Carolina

Slide 36

Clastic Depositional SimulationClastic Depositional Simulation


























































































Geometric Effects of Sea Level ChangeGeometric Effects of Sea Level Change

On-lap with rising sea level.

Off-lap with falling sea level.

By-pass at low stands of sea level.

Erosion at low stands of sea level.


Erosion at low stands of sea level.

Ravinement with sea level transgressions.

Landward continental clastics at high stands.

Seaward carbonates at high stands.



Chronostratigraphic ChartChronostratigraphic Chart





Slide 69


Slide 70


Slide 71


Slide 72


Slide 73


Slide 74


Slide 75


Slide 76


Slide 77


Slide 78


Slide 79


Slide 80


Slide 81


Slide 82


Slide 83


Slide 84


Slide 85


Slide 86


Slide 87


Slide 88


Slide 89


Slide 90


Slide 91


Slide 9


Slide 93


Slide 94


Slide 95


Slide 96


Slide 97


Slide 98

Sokari BraidePetroleum Geology 1Petroleum Geology 1And how it all can be viewed in outcrop:

Karoo Basin, South Africa


Department of Earth Scienceshttp://www.liv.ac.uk/-rwild/index.htm

From Karoo Basin Slope Project (University of Liverpool, UK)

Slide 99




Sokari Braide

I grant anyone the right to use this work for any purpose, without any conditions, unless such conditions are required by law. This applies worldwide.

Documents

Lecture 14_Petroleum Geology_Sokari Braide (2)