Chapter 08 Chapter 08 HABITA OF THETHE HABITA OF HYDROCARBONS IN HYDROCARBONS IN SEDIMENTARY BASINS SEDIMENTARY BASINS
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Introduction
There are approximately 600 sedimentary rock basins in the world.
A quarter of them are producing petroleum
Before exploitating in a new area, attemting to locate drillabe prospects, it is necessery to establish the type of basin, what productive horizons it may contain and where they may be broadly located
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• Even though petroleum reserves can be found in rocks of all ages, most giant fields and most of the world's reserves occur in sequences, of Late Mesozoic and Cenozoic age ( Figure ) . Paleozoic rocks probably had potential to generate hydrocarbons equal to that of these younger rocks, but there has been more time in which to destroy all or part of the petroleum through uplift and erosion (Halbouty et al, 1970).
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• Worldwide reserves can be related to their location within a
petroleum basin, regardless of its basin type (Figure )
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8.1-The Sedimentary Basin Concept
• A general term for any large area of tectonic origin
with a thick accumulation of sedimentary rocks.
• A basin is a geological structure with a unique sequence of rocks that are dissimilar to those outside the basin.
• A low area with no exterior drainage.
• Include both depression itself and the thicker-than-
everage sediments that fill it
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Idealized pattern of a sedimentary basin
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Sedimentation patterns over arch, shelf and basin
Main content:
• Geometry of Sedimentary Basins • Sediment Fill • Tectonic Processes and Timing • Basin-Forming Mechanisms • Sedimentary Basin Classification
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Geometry of Sedimentary Basins Geometry of Sedimentary Basins
It is tempting to believe that a sedimentary basin was deepest where its sediments are thickest, but this is not necessarily true
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Non-coincidence of depocenters, topographic low and point of maximum basement 1111 subsidence in a land-derived, prograding clastic wedge
Sediment Fill Sediment Fill Basins can be characterized by the sediments that fill
them.
They can be dominated by continental, shallow
marine, or deep marine sediments, depending on their elevation and the interplay between the rate of subsidence and the rate of sedimentation
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Tectonic Processes and Timing Tectonic Processes and Timing
• An important aspect of sedimentary basins is the
nature and timing of tectonic processes.
• The types of folds and faults that develop within a
basin are partly due to deformation mechanisms and partly to its sediments
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Forming Mechanisms BasinBasin--Forming Mechanisms
• Basins form as a result of large-scale vertical and horizontal movements within the earth's upper layers, which can be explained through the widely accepted theory of plate tectonics.
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• The earth's outermost shell is a rigid layer
called the lithosphere, which consists of crust and uppermost mantle. Topographic lows form on the earth's surface where the crust is thin, and composed of dense basaltic rocks
• The rigid lithosphere overlies a less viscous
layer called the asthenosphere
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The earth's outermost layers
Distribution of lithospheric plates, showing relative velocity and direction of plate separation and convergence in centimeters per year 1717
Initiation of rifting and ocean floor spreading over Initiation of rifting and ocean floor spreading over
continental crus continental crus
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Pre-rift domal bulge
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Innitial radial rift
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Early separation stage
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MODEL OF A DIVERGING PLATE BOUNDARY MODEL OF A DIVERGING PLATE BOUNDARY
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The separated continents are now far apart, and basins develop along their passive margins
MODEL OF SUBDUCTING PLATE MARGIN MODEL OF SUBDUCTING PLATE MARGIN
At a subduction zone, the leading edge of one plate overrides another, and the overridden plate is dragged down into the mantle and consumed
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MODEL OF A COLLISIONAL PLATE MARGIN, SHOWING COLLISION MODEL OF A COLLISIONAL PLATE MARGIN, SHOWING COLLISION BETWEEN OCEAN PLATE AND A CONTINENTAL MARGIN BETWEEN OCEAN PLATE AND A CONTINENTAL MARGIN
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MODEL OF A COLLISIONAL PLATE MARGIN, MODEL OF A COLLISIONAL PLATE MARGIN, CONTINENT COLLISION SHOWING CONTINENT –– CONTINENT COLLISION SHOWING CONTINENT
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Transcurrent faulting along the conver. plate margin in Californiaia Transcurrent faulting along the conver. plate margin in Californ
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In summary, there are three fundamential types of plate boundaries:
• MID-OCEAN RIDGES
• SUBDUCTION ZONES AND SUTURES
• TRANSCURRENT FAULTS
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Sedimentary Basin Classification 8.28.2--Sedimentary Basin Classification
• Many different basin classification schemes
have been proposed, as geological thought has evolved from the geosyncline concept to plate tectonics.
• In the petroleum industry, a classification is
needed that emphasizes the role of the sedimentary basin as a container for oil and gas.
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There are a total of ten basin types:
• two that are related to stable continental plates; • two that develop through plate divergence; • four that relate to plate convergence. • Two other types, basins that downwarp into small oceans, form a separate class because of their unique petroleum features.
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Basin classification Basin classification
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Idealized pattern of an Interior basin
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Generalized cross-section through the Williston basin of the USA and Canada
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Geometry of the world;s interior basins
Major interior basins of the world
Major interior basins of the world
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Table 10.1. Interior Basin (Intracratonic, sag) • Distinguishing features-- simple, single cycle; no uplands; in
continental interiors.
• Depositional History-- mature, shallow water to non-marine
sediments (clastic or carbonate prone); non-depositional or non- marine late stage.
• Reservoir-- equally sandstone or carbonate. • Source-- shale. • Cap-- shale, less commonly evaporite. • Trap-- basement uplift arches and anticlines; combination and
stratigraphic.
• Geothermal Gradient-- low to normal. • Hydrocarbons-- low S, high gravity crude low natural gas. • Risks-- adequate traps; presence of shale for source and cap. • Typical Reserves-- <0.5- 3 billion bbl hydrocarbon/basin.
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Idealized pattern of a foreland basin
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A typical foreland basin: The Permian basin of west Texas
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Table 10. 2 Foreland Basin (craton margin, composite)
• Distinguishing features-- multicycle basin on craton edge with
adjacent uplift.
• Depositional History-- 1st cycle mature platform sediments;
unconformity; 2nd cycle orogenic clastics.
• Reservoir-- mostly sandstone, lesser carbonate; in both cycles. • Source-- overlying or interfingering shale; locally coal. • Cap-- shale or evaporite. • Trap-- mostly anticlines; some stratigraphic and combination . • Geothermal Gradient-- low to above average. • Hydrocarbons-- mixed crude, similar to interior basins in 1t cycle;
above average deep thermal gas.
• Risks-- trap efficiency; reservoir, source and seal development. • Typical Reserves-- <0.5- 5 billion bbl hydrocarbon/basin.
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Rift Basin Rift Basin
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Idealized pattern of a rift basin
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The Suez basin of Egypt contained mostly thin Paleozoic and Cretaceous non-marine sands until it began to rift in the Cenozoic
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• Table 10.3. Rift Basin
• Distinguishing features-- downdropped graben over continental
crust; dormant divergence.
• Depositional History-- pre-rift rocks sedimentary, metamorphic or
granitic; post-rift fill is restricted facies, initially non-marine that may become marine (either clastic or carbonate-prone).
• Reservoir-- equally sandstone or carbonate; of pre- and post-rift
cycles.
• Source-- overlying or lateral facies shale. • Cap-- basinwide evaporites or thick shale. • Trap-- horst block anticlines; combination traps related high blocks;
tilted fault blocks.
• Geothermal Gradient-- normal to high. • Hydrocarbons-- highly facies-dependent(paraffinic with sandstone's;
aromatic with carbonates); low to average gas.
• Risks-- small trap size; too high gradient; source shale development. • Typical Reserves-- <0.5- 30 billion bbl hydrocarbon/basin.
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Apart Basin (passive margin, PullPull--Apart Basin (passive margin, divergent margin) divergent margin)
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Idealized pattern of a pull-apart basin
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The Gabon basin off the west coast of Africa The Gabon basin off the west coast of Africa
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Table 10.4. Pull-Apart Basin (passive margin, divergent margin)
• Distinguishing features-- coastal half-grabens down-faulted seaward;
intermediate crust; result of ocean-floor spreading.
• Depositional History-- non-marine rift stage sediments; restricted facies (carbonates, evaporites, black shale) in early separation; prograding clastic wedge in late separation stage.
• Reservoir-- sandstone in all three stages, some limestone in early
separation stage.
• Source-- overlying and interfingering shale. • Cap-- shale or evaporite. • Trap-- horst block, salt flow, roll-over and drape anticlines;
stratigraphic and combination .
• Geothermal Gradient-- below average in marine stages. • Hydrocarbons-- rift stage has paraffinic, intermediate gravity crude;
more aromatic, light gravity in separation stage; gas prone.
• Risks-- kerogen maturation; biodegradation; pre-separation source
shales; post-separation reservoirs
• Typical Reserves-- 2-3 billion bbl hydrocarbon/basin.
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Convergent Margin Basins: Fore--Arc, Arc, Convergent Margin Basins: Fore
BackBack--Arc, Non
Arc and Arc, Non--Arc and
Collision Basins Collision Basins
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• There are two types of basins that are found near subduction zones that have developed island-arcs.
• Back-arc basins form between an island-arc and continent (Figure , Idealized pattern of a back-arc basin). They receive mostly shallow water sediments. Heat flow measured from back-arc basins is high to very high, because of the melting and igneous activity of the island- arc.
• Fore-arc basins lie between the island-arc and the ocean trench. Their sediment facies are quite variable and can range from fluvial to deep-sea fan. In contrast to back-arc basins, fore-arc basins have abnormally low heat flow, because of the underthrusting of the cool ocean plate.
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Idealized pattern of a fore-arc basin (lie between the island-arc and the ocean trench)
Idealized pattern of a back-arc basin (form between an island-arc and continent )
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• Indonesia provides a good example of these
subduction zone basins (Fig.).
• Several back-arc basins have developed behind the island-arc and adjacent to the stable continental Sunda Shelf. Smaller, fore-arc basins are found in front of the island-arc. Both types run parallel to the trench-arc system, where the northward- moving Australian plate is being overridden by Eurasia.
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Basins and tectonic elements of Indonesia Basins and tectonic elements of Indonesia
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•A cross section through the Sumatra back-arc and Mentawai fore-arc basins illustrates the facies and petroleum habitat •The Sumatra basin is filled with up to 5 kilometers of late Tertiary prograding clastic sediments, with only small amounts of limestone. However, because of the very high heat flow, even such young sediments are oil-productive at depths of less than a kilometer. Production comes from sandstone of Pliocene and late Miocene age, trapped in compaction structures over the uneven basement topography and, higher in the sequence, in anticlines. Thick inter fingering and overlying deepwater shales are the petroleum source.
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In contrast, the fore-arc Mentawai basin contains mostly shales and volcaniclastic sediments, but also has thick carbonate banks and reefs (Seely and Dickinson, 1977). This basin is relatively shallow, has a low heat flow, and is not commercially productive. A major reason for this is the lower-than- normal thermal gradient, caused by the descent of the cool oceanic plate. Also the volcaniclastic sediments of fore-arc basins have poor porosities, when compared to the more reworked back-arc sands.
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Generalized cross-section through the Sumatra (back-arc) and Mentawai (fore-arc) basins of Indonesia
Arc Basins NonNon--Arc Basins
• Non-arc basins are formed along convergent
margins where the plates move by transcurrent faulting
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Idealized pattern of a Non-arc basin
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Collision Basins Collision Basins
• Collision basins, sometimes called median,
intermontane, or successor basins, are small basins formed within marginal fold-belts, along sutures where either two continents, or continental coastal mountains and a trench, have collided
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Idealized pattern of a collision basin
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Table 10.5. Convergent Margin Basins
B back-arc
C non-arc (strike-slip, California-type)
A fore-arc D collision (median, intermontane, successor)
• Distinguishing features-- small, deep, young; local extension and strike
slip in regional compression along convergent plate margins.
• Depositional History-- immature, poorly sorted clastic sediments; rapidly intertonguing facies; shallow to deep and/or volcanistic. • Reservoir-- thick sandstones, often multiple; minor reefal limestone. • Source-- abundant, thick interbedded shale. • Cap-- shale. • Trap-- drape and compression anticlines, strike-slip and thrust structures;
reefs; horst-related combination..
• Geothermal Gradient-- low (A); high (B,C); or normal to high (D). • Hydrocarbons-- mostly paraffinic to paraffinic-naphthenic; variable
gravity; low natural gas..
• Risks-- maturation; leakage; deformation too intense; igneous activity;
poor reservoir properties.
• Typical Reserves-- <0.5- 12 billion bbl hydrocarbon/basin.
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Downwarp Basin Downwarp Basin
Sedimentary basins that are downwarps into small oceans are in a separate class, because their sediments and petroleum characteristics are often very different from other basin types to which they are genetically related
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Idealizaed pattern of a downwarp basin
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Geometry of the world's downwarp basins
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Major downwarp basins of the world
Generalized cross-section through the Gulf Coast basin, Southern USA and Gulf of Mexico
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Generalized cross-section through the Arabian-Iranian basin
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Table 10.6. Downwarp Basin
A Open-- related to pull-apart, passive margins B Closed-- related to foreland basins
C Trough-- related to foreland basins
• Distinguishing features-- basement and depositional downwarp dipping into small
oceans, inland seas or linear suture zones; intermediate crust.
• Depositional History-- mixed, interfingering shallow marine facies, either carbonate or
clastic-prone.
• Reservoir-- carbonate (C); or mixed (A,B) with sandstone (A) or carbonate (B)
dominant.
• Source-- overlying, interfingering and basin-center shales; limestone and marls
important in B.
• Cap-- mostly shale; both shale and evaporites in B. • Trap-- anticlines; salt flow; combination; reefs, pinch-outs and unconformities. • Geothermal Gradient-- normal to above average. • Hydrocarbons-- intermediate to mixed gravity crudes; sandstones more paraffinic,
carbonates more aromatic; average to high natural gas.
• Risks-- maturation; leakage; deformation too intense; igneous activity; poor reservoir
properties.
• Typical Reserves-- 4- 40 billion bbl hydrocarbon/basin (A); 10- >50 (B), .5- 3 (C).
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Tertiary Deltas Tertiary Deltas
In a sense, tertiary-age deltas are not true basins but later overprints onto other basin types. They can form in any coastal setting, and are found about equally over convergent and divergent margins
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Idealized pattern of a Tertiary age delta
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Major delta basins of the world
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Geometry of the world's Tertiary deltas
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Generalized cross-section through the Niger delta of west Africa 8383
Tertiary Delta Table Tertiary Delta Table
Distinguishing features: circular depocenter basin; on plate triple junction where failed arm rift meets ocean basin, particularly at divergent or transcurrent margin.
Depositional History: prograding wedge of land-derived clastics with
Type III kerogen.
Reservoir: sandstone (pro-delta facies) Source: shale. Cap: shale. Trap: roll over anticlines; growth faults, mud or salt diapirs; sand
lenses.
Geothermal Gradient: low. Hydrocarbons: paraffinic to paraffinic-naphthenic crude; very high
natural gas.
Risks: small trap size, adequate caprock. Typical Reserves: to 20 billion bbl hydrocarbon/basin; few fully
developed.
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IDENTIFICATION PARAMETERS IDENTIFICATION PARAMETERS OF BASIN MODELS OF BASIN MODELS
• Continental or oceanic crust (basement)
underlying basin.
• Type of past plate movement involved in basin
formation (divergent or convergent).
• Basin/cycle position on plate and primary structural movement involved in basin origination.
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DISTRIBUTION OF PETROLEUM – RICH BASINS Together the 25 sedimentary basins in the world, which are the richest in terms of known petroleum reserves, contain nearly 90% of the world's oil and gas. A breakdown of these petroleum-rich basins by basin type shows that eight of them belong to the downwarp basin class, and an additional seven are large foreland basins Of the remaining ten, three of the basins are rifts and two are deltas. Finally, there are five convergent margin basins, including three non-arc, one back-arc, and one collision basin type. Only three basin types are not found among the world's richest petroleum basins: the interior, the pull-apart, and the fore-arc basins.
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Richest petroleum basins
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Histogram divides the total world sediment volume Histogram divides the total world sediment volume
within this depth range, by basin type within this depth range, by basin type
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Distribution of P.reserves with depth for each of the basin types
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Percent of all P. producing basins within each basin type that contains giant fields 9191
Exercise Exercise
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