Petroleum Geoscience and Geophysics Chapter 2
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Transcript of Petroleum Geoscience and Geophysics Chapter 2
![Page 1: Petroleum Geoscience and Geophysics Chapter 2](https://reader034.fdocuments.in/reader034/viewer/2022051020/5695d2851a28ab9b029ac0bc/html5/thumbnails/1.jpg)
CHAPTER 2
• SEDIMENTARY BASINS
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Sedimentary Basins
• Sedimentary basin: a low area of the earth’s
surface underlain by a thick sequence of
sedimentary rocks.
• Basin Types:
• 1. Extensional basins (divergent plate motion)
• Two main mechanisms operate to create
extensional basins. First, rifting can occur when
a thermal plume or sheet impinges on the base
of the lithosphere (active rifting).
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Sedimentary Basins
• Rift basins:
• Form as a direct result of crustal tension at the
zones of seafloor spreading.
• A rift basin is bounded by a major fault systems
(grabens).
• A number of rift basins; including Baikal rift,
Red Sea, North Sea, and Central Africa rift
valleys extending from Nigeria, Mozambique,
and Somalia.
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• The lithosphere
heats up,
weakens, and can
rift. An example is
the East African
Rift.
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Sedimentary Basins
• The second mechanism (passive rifting) is
continental stretching and thinning, which has
happened during all major continental
breakups.
• The most widely recognized pair of passive
margins are South America and Africa.
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Passive Rifting
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Sedimentary Basins
• Passive basins:
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Sedimentary Basins
• Intracratonic basins: sag.
• Intracratonic (intracontinental) basins were
regarded as somewhat enigmatic. Their
alternative description, "sags," illustrates their
form. Most tend to be broadly oval, shallow,
saucer-shaped basins .
• The total sediment infill package increases
from edge to center and major faults are
absence.
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Sedimentary Basins
• Intracratonic basins generally contain abundant reservoir rocks in both terrigenous and carbonate facies.
• Source rocks tend to be poorly developed, except in the more marine carbonate basins.
• Because these basins occur on stable granitic crust, heat flow rates are low and major oil generation may not have oocurred.
• Siries of Intracratonic basins occur in North
Africa, eg: Murzuq and Kufra basins
(terrigenous basins). Another example is the
Michigan basin (carbonate basin).
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Intracratonic
basins –
Murzuq
basin, Libya
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Malay Basin
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Sedimentary Basins
• Epicratonic basins: basins that lie on the edge of continental crust.
• The Tertiary Gulf Coast of the US and the Niger
delta illustrate a terrigenous epicratonic basin,
and the Sirte embayment of Libya illustrates a
carbonate-filled basin.
• Epicratonic basins show that they are more
prospective than intracratonic basins.
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Sedimentary Basins
• Heat flow is high, which favors hc generation in
areas of high geothermal gradients due to
overpressure.
• Crustal instability also favors structural
entrapment of oil, as well as stratigraphic traps.
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Epicratonic Basins
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Sedimentary Basins
• 2. Basin generated during convergent plate motion:
• The style of basin development associated with
convergent plate motion is highly varied, and
depends upon the interplay of several factors.
• These include the types of crust undergoing
convergence: continental to continental, oceanic
to oceanic, and oceanic to continental.
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Sedimentary Basins
• Arc Systems or Troughs:
• Characterized by six major components.
i) An outer rise on the oceanic plate.
This occurs as an arch on the abyssal plain.
ii) A trench.
Commonly > 10km deep, the trench contains pelagic deposits and fine-grain turbidites.
Not considered to be prospective for petroleum exploration.
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Sedimentary Basins
iii) A subduction complex.
Comprises stacked fragments of oceanic crust and its pelagic cover.
iv) A fore-arc basin.
Lies between the subduction complex and the volcanic arc.
Less productive hc provinces than do back-arc basins.
v) The volcanic (magmatic) arc.
• Magma is generated from the partial melting of
the overriding and possibly subducting plates.
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Overriding plate at a subduction zone
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Forearc Basin
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Sedimentary Basins
6. The back-arc region.
Floored by either oceanic or continental lithosphere. Back-arc basins floored by oceanic lithosphere tend to have very high rates of subsidence and high heat flows.
• Foreland basins: Where the back-arc region is floored by continental lithosphere.
The deposits are shallow marine shales, carbonates and tidal shelf sands.
Combination of favorable reservoir rocks, source rocks, and traps diversity, back-arc basins are commonly major hc provinces.
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Sedimentary Basins
• The Central Sumatra Basin is well-described
example. Other examples are Persian Gulf,
Western Canada and South East Asia.
• The importance of foreland basins as petroleum
provinces outranks that of other basins
generated by convergent plate motions.
• The basins are typically several thousands of
kilometers long and parallel to the arc and thrust
belt.
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Sedimentary Basins
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Sedimentary Basins
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A simplified map and cross-section of the Zagros orogenic belt (Iran).
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NNE-SSW diagrammatic cross-section to suggest the plate-tectonic model of
South China Sea Basin for Early Cretaceous toMiddle Eocene convergent
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Sedimentary Basins
• 3. Strike-slip basins:
• Strike-slip or wrench basins occur where
sections of the crust move laterally with respect
to each other.
• Although a wrench system taken as a whole can
be of similar size to a rift, passive margin, or
foreland complex, individual basins are much
smaller than the other types of basin described
before.
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Sedimentary Basins
A strike-slip basin plan and crosssection,
showing typical megasequence
distributions for the syn-rift, post-rift, and
transpression stages of the basin.
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Sedimentary Basins:
Malay basin