Marine Depositional Environments Basics Marine Carbonates
Depositional Environments
(Last Updated 28 December 2015)
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Marine DepositionalEnvironments Basics
Marine Carbonates Depositional Environments
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Depositional Environments
Processes and examples from modern and ancient environments with oil field examples– Subaerial
Alluvial fanFluvial – braided and meanderingAeolian – wind and desert
– Marginal marineDelta – river, wave, tide dominated, fan delta, braid deltaBeach and barrier island
– MarineSubmarine fan – channel-levee complex, Bouma
sequenceCarbonates – limestone, dolomite
Reef, platform, pinnacle, pelagicDiagenesis
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Marine Carbonates Depositional Environments
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Objectives of the Carbonates Session
You will learn about:– Environments of carbonate deposition
Reef
Shelf
Pinnacle
Ramp
Pelagic
– Factors that regulate carbonate depositionWater temperature
Turbulence
Organisms
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Rock Type Abundance and Production by Rock Type
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Marine Carbonates Depositional Environments
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Environments of Deposition for Carbonates
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Carbonate Classification Scheme
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Environments of Deposition for Carbonates
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Selected Environments of Deposition for Marine Carbonates
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Textures Expected Basinward of the Platform Rim
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Carbonate Mudstone
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Pelagic Limestone from the North Sea
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Fine-textured limestone consisting of calcareous tests (shells) of floating organisms deposited mostly in basins, but sometimes on shelves.
Can have high porosity but typically low permeability.
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Late Cretaceous Chalk Outcrop: Etretat, France
Note: Cliff is approx. 120 m cliffin height.
Same age as the “White Cliffs of Dover” on the other side of the English Channel.
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Ekofisk Field, Central Graben, North Sea
An example of production from pelagic limestones.
5.5+ TCF Gas3.4 BBO+ NGLs
Discovered in 1969 by Phillips PetroleumCompany
244 m (801 ft) of vertical closure and a hydrocarbon column 305 m (1,001 ft) long, formed by Permian Zechstein salt movement in the form of salt pillows
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Cretaceous and Paleocene Aged Chalks
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1960s–1970s Vintage Seismic Line Over Ekofisk Field
Ekofisk structureappears to havecollapsed with alow developedover what wouldhave been the structural crestof the field.
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Original Structure Map Over Ekofisk Based on Seismic
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Log Cross Sections Over Ekofisk Field
Note: Well control indicates there is no structural low but simply a large anticlinal structure.
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Post Drilling and Seismic Reinterpretation of Ekofisk
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Gas “Cloud” Over Crest of Structure Causes Low Velocity
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Carbonate Deposits Near the Rim (Reef)
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Carbonate Deposits Near the High Energy Rim (Reef)
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Belize Barrier Reef: A Rimmed Shelf
Water depth to left is 100+m (300′ +).
Behind reef, depth 4–5m (18′).
Over reef, where you see waves, the water is less than 2′ (0.6m).
Reef is 200km long and the shelf is 40km wide.
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Belize Barrier Reef: Robust Corals Growing
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Belize Barrier Reef: Mostly Dead Reef Material
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Notice 4.5 foot long Morey Eel
Very large porespaces in Boundstones if pore space could be preserved
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El Capitan Reef Complex, Guadalupe Peak, West Texas
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Basin to Reef Crestpreserved with2000 feet ofexposed rock
The perfect place to studycarbonates…the West TexasDesert.
So why doeseveryone wantto go on fieldtrips toBelize and theBahamas?
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El Capitan and Delaware Basin Stratigraphy
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Textures Behind a Rim or on a Platform
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Carbonate Facies Belts with Representative Textural Types
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Oolites: Form in Areas of Higher Energy Agitated Waters
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Oolites: In Thin Section, Notice Seed Crystal in Centers
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Oolite Shoal in the Bahamas:Potentially 225 sq. km of Potential Reservoir
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Distribution of Cretaceous Carbonate Platforms on Cretaceous (100Mya) Plate Positions
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Quiet Water Lagoonal Facies
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Dry Tortugas, 120 Miles From Land East of Florida
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Laterally extensive, shallow carbonate shelf, 120 miles from land…no clastics.
Mostly carbonate mudstones.
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Patch Reefs near Blue Hole, Lighthouse Reef, Belize
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Small Patch Reef Within Platform Carbonates: Saudi Arabia
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Textures Behind a Rim or on a Platform
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Green Algae that Creates Sandsize to Claysize Carbonate
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Green Algae that Creates Sandsize to Claysize Carbonate
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CaCO3 secreting algae: yield >85% sand and clay size particles
Halimeda: bottom right example – Sand size plates
Pennicillus: fan shaped – Clay size plates
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Green Algae that Creates Sandsize to Claysize Carbonate
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Sand Sized Carbonate Pellets Due to the Action of Worms
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Thin section of a Carbonate Pellet Grainstone –sand size
Worms and their effects
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Monotonous Lagoonal Carbonates West of San Antonio, Texas
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What is the effect on shelf deposits when there are multiple cycles of rising and falling sea level?
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Humid, Carbonate, Rimmed Shelf
Porosity development in low stand due to dissolution of exposed carbonate system.
Organics deposited in high stand during flooding.
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Blue Hole, Lighthouse Reef, Belize
The Blue Hole…A mystical place from those in Belize.
Water depth at rim is 10′—hole is 340′ deep, diameter is 1000′ (300m).
Possibly related to Pleistocene lowstand.
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Blue Hole, Lighthouse Reef, Belize
At a depth of 130–170 feet, there are
stalactites and stalagmites.
These only form in the presence of air with dripping water, typically in caves.
Sea level during last glaciation about 340 feet deeper than today.
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Devonian carbonates and two wells in the Canning Basin, Australia, show the stacking of sedimentary units and repetition of systems tracts generated by cyclical rises and falls on sea level
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Devonian Platform Distribution, Canning Basin, Australia
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Devonian Platform Distribution, Canning Basin, Australia
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Stacked Sequences in two Wells in the Canning Basin, Australia
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Sequence Model of the Frasnian-Famennian (Devonian) Reef Complex, Canning Basin, Australia
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Productive Examples of Carbonate Platforms
Ghawar Field on Arabian Platform
Largest producing Oil and Gas field in the world
Production from several levels
174 miles by 19 miles in aerial expent
OOIP of 200 billion barrels?
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Diagrammatic of Permian Carbonate Depositional Environments
Great lateral extent of Permian environments on Arabian platform “restricted, evaporitic facies”
Less than 15′ water, mostly algae producing fine grained carbonates
Compressional fault bounded structure related to Arabian-Asian plate collision
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Map of Khuff-C (Permian) Gas on the Ghawar Structure
Cross section of sonic logs on next slide
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Khuff-C Porosity Distribution
Sonic Logs over Ghawar showingPorosity change in the Khuff-C Reservoir
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Thin sections of porous and nonporous Khuff-C Reservoir
PelletoidalGrainstone… i.e. Worm excrement
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Carbonate Buildups Can Also Make Detached Shelves
Starts in shallow water and keeps up...creates “platform”
Ultimate drowning
This example is from Australia.
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The sediments and stratigraphic characteristics of detached carbonate platforms approximate those attached platforms
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Depositional Sequence Model Detached, Humid Rimmed Platform
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Petroleum production from detached carbonate platforms
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Depositional Sequence Model Detached, Humid Rimmed Platform
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Seismic Line Across Tengiz Structure
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3D Seismic Across Tengiz Structure
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Geological Model of Tengiz Field Post Drilling and 3D
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Pinnacle Reef
Another kind of reef
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Selected Environments of Deposition for Marine Carbonates
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Reef Types
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Production from pinnacle reefs
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Kasmin Utara and Kasmin Reefs, Indonesia
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Intisar Fields, Sirte Basin Libya
Oxy drilled Intisar field in Libya2mi across (small)950′ oils column
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Intisar D: Field, Sirte Basin Libya
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Intisar D: Field, Sirte Basin Libya
Just off Intisar reef structure—hard to see except for some minor shallow structure
Flat under reef
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Intisar “D: Field, Sirte Basin Libya
Over the “core” of the Intisar reef structure see drape, low compaction reef
Also see “pull down” below reef due to porosity in carbonates and/or weight of reef
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North Field, Offshore Qatar and Iran
Carbonate Ramps—North Field off Qatar…filled to spill and largest gas field in the world
Conoco originally offered entire lease, 3 interpreters because so big and “NO” structure; gave up lease
Exxon and Shell picked it up and put the 3 pieces together properly
Reserves on the order of 1.3 Quadrillion cubic feet
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Environments of Deposition for Carbonates
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Ras Tanura Beach, Saudi Arabia, North of Worlds Largest Refinery
Oolitic sand and siliciclastic beach.
Sands brought in by long shore transport from a delta 300 miles to the north.
Note: Right where wave breaks, water goes cloudy, and then after break, water goes clear…release of CO2 due to waves and precipitation of carbonates, then back into solution.
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Near road to Ras Tanura, Saudi ArabiaTidal channel with CaCO3 precipitating in water (notice cloudy appearance)
Water temp 95 degrees F (38–39 C?)
Note Beachrock – early diagenesis (lithification) and maybe Dolomitization
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Windward Side of Bush Key, Dry Tortugas
Boundstoneparent material
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Bioclastic Limestone of Crinoid Stems and Fragments
Completely cemented
0 por/perm
Super hard—hit with hammerand be sorry—
Good for making tombstone
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Sarasota, Florida
Coquina in the making
Note preferred orientation of shells.
Impact on Kh>Kv ?
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Environments of Deposition for Carbonates
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Supratidal Deposition (Sabhka)
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Algal Mat, Potential Source: Abu Dhabi, UAECyanobacteria and fungi, found just above high tide line, covered with dust
Blooms when wet—turns green
One of the best source rocks there is and been there for last 120 mm years—interbedded with reservoir produces only sweet crude
2–3 mm thick
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Up Close Algal Mat, Potential Source: Abu Dhabi, UAE
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Algal Mat, Potential Source: Abu Dhabi, UAE
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Objectives of the Carbonates Session
You have learned about:– Environments of carbonate deposition
Reef
Shelf
Pinnacle
Ramp
Pelagic
– Factors that regulate carbonate depositionWater temperature
Turbulence
Organisms
90
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Marine Carbonates Depositional Environments
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Exercise
Interpreting Carbonate Environments from Seismic
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