THE HABITAT OF HYDROCARBONS IN SEDIMENTARY BASINS (cơ sở KHOA học địa CHẤT dầu KHÍ SLIDE TIẾNG ANH)

• two other types, basins that downwarp Open & closed into small oceans, form a separate class because of their unique petroleum features... 2 Foreland Basin craton margin, composite •

THE HABITAT OF HYDROCARBONS IN SEDIMENTARY BASINS

Chapter 08:

is necessery to establish the type of

basin, what productive horizons it may contain and where they may be broadly located

• 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 01)

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).

4

Fig: 01

• Worldwide reserves can be related to their

location within a petroleum basin, regardless of

its basin type (Figure: 02)

6

Fig: 02

8.1-The Sedimentary Basin Concept

• A general term for any large area of

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

Idealized pattern of a sedimentary basin

Fig: 03

Sedimentation patterns over arch, shelf and basin

Fig: 04

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

Non-coincidence of depocenters, topographic low and point of maximum basement subsidence in a land-derived, prograding clastic wedge

Fig: 05

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

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

Basin-Forming Mechanisms

• Basins form as a result of large-scale

vertical and horizontal movements

within the earth's upper layers (fig 1) , which can be explained through the widely accepted theory of plate

06-tectonics

Fig: 06-1

• 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

The earth's outermost layers

Fig: 06-2

Distribution of lithospheric plates, showing relative velocity

and direction of plate separation and convergence in

centimeters per year Fig: 07

Initial radial rift

Fig: 09

Early separation stage

Fig: 10

MODEL OF A DIVERGING PLATE BOUNDARY

The separated continents are now far apart, and basins develop along their

passive margins

Fig: 12

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

Fig: 12

MODEL OF A COLLISIONAL PLATE MARGIN,

SHOWING CONTINENT – CONTINENT

COLLISION

Fig: 14

Transcurrent faulting along the conver plate margin in

California

Fig: 15

8.2-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.

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 (Open & closed) into small

oceans, form a separate class because of their unique petroleum features

Basin classification

Fig: 16

Basin types and details

31

Stable continental

plates:

• Interior Basin

32

Idealized pattern of an Interior basin

Fig: 17

Generalized cross-section through the Williston basin of the USA and Canada

Fig: 18

Major interior basins of the world

Major interior basins of the world

Fig: 20

• 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

Foreland basin:

37

plates:

Idealized pattern of a foreland basin

Fig: 21

A typical foreland basin: The Permian basin of west Texas

Fig: 22

Fig: 24

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

Fig: 26

Idealized pattern of a rift basin

Fig: 28

The Suez basin of Egypt contained mostly thin Paleozoic and Cretaceous non-marine sands until it began to rift in the Cenozoic

Fig: 29

46 The CuuLong basin of Vietnam

• 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

Idealized pattern of a pull-apart basin

Fig: 30

Fig: 32

The Gabon basin off the west coast of Africa

Fig: 33

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

• 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 34 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.

Idealized pattern of a back-arc basin

(form between an island-arc and

continent )

Idealized pattern of a fore-arc basin

( lie between the island-arc and the

ocean trench)

Fig: 34

• Indonesia provides a good example of

these subduction zone basins (Fig.35)

• 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

Basins and tectonic elements of Indonesia

Fig: 35

•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.

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

Generalized cross-section through the Sumatra arc) and Mentawai (fore-arc) basins of Indonesia

(back-Fig: 36

• Non-arc basins are formed along convergent

margins where the plates move by transcurrent faulting

• Consequently, they are sometimes called

strike-slip basins They are also called California-type

basins, because they are common along the west

coast of the United States

• Non-arc basins are small basins that form through

a combination of both the transcurrent fault

movements and local block-faulting In addition to the California basins, non-arc basins include the Vienna basin, and the Crimea and Baku basins of the Soviet Union

Idealized pattern of a Non-arc basin

Fig: 37

Fig: 38

Fig: 40

Fore-Arc

Back-Arc Non-Arc Collision Basins

Convergent Margin

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

Idealized pattern of a collision basin Fig: 41

Fig: 42

Table 10.5 Convergent Margin Basins

A fore-arc B back-arc C non-arc (strike-slip, California-type)

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

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,

- Open- related to pull-apart, passive

margins

- Closed- related to foreland basins

- Trough- related to foreland basins

Idealizaed pattern of a downwarp basin

Fig: 43

Major downwarp basins of the world

Fig: 45

Generalized cross-section through the Gulf Coast basin, Southern USA

and Gulf of Mexico

Fig: 46

Generalized cross-section through the Arabian-Iranian basin

Fig: 47

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)

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

Idealized pattern of a Tertiary age delta Fig: 48

Major delta basins of the world Fig: 49

Fig 50: Generalized cross-section through the Niger delta of west Africa

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.