GIAO TRINH CHAPTER 8

MODEL OF A DIVERGING PLATE BOUNDARY The separated continents are now far apart, and basins develop along their passive margins Fig: 12... Rift Bas in; Pull-Apart Bas in pas s ive marg

THE HABITAT OF HYDROCARBONS IN SEDIMENTARY BASINS

Chapter 08:

Conte nt

Intro duc tion

8.1-The Se dime ntary Bas in Co nce pt

8.2-Sedime ntary Bas in Clas s ific ation

8.3-Dis tributio n o f petrole um – ric h

bas ins

2

Intro duc tion

There are approximately 600 sedimentary rock basins in the world.

A quarte r o f the m are producing pe tro le um

Before exploitating in a new area, attemting to

lo cate drillabe pro s pe cts , it is necessery to

e s tablis h the type o f bas in, what productive

horizons it may co ntain and where they may

be broadly located

• Even though petroleum reserves can be

found in rocks of all ages, mos t 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 Se dime ntary Bas in Co nce pt

• A general term for any large area of tectonic

orig in with a thick ac cumulatio n of

s edime ntary roc ks

• 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

Main c o nte nt:

1.Geo me try o f Sedimentary Bas ins

2.Se dime nt Fill

3.Te c to nic Proc es s e s and Timing

4.Bas in-Fo rming Me chanis ms

5.Se dime ntary Bas in Clas s ific atio n

Ge ome try of S e dime ntary Bas ins

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

Se dime nt 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

Te c tonic Proc e s s e s 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

Bas in-Forming Me c hanis ms

• Basins form as a result of large-scale vertical and horizontal movements within the earth's upper layers (fig 06-1) , which can be

explained through the widely accepted theory

of plate 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 lithos phere overlies a les s

vis c o us layer called the as thenos phere

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 COLLIS IONAL PLATE MARGIN, S HOWING COLLIS ION

BETWEEN OCEAN PLATE AND A CONTINENTAL MARGIN

Fig: 13

MODEL OF A COLLISIONAL PLATE MARGIN,

SHOWING CONTINENT – CONTINENT COLLISION

Fig: 14

Transcurrent faulting along the conver plate m argin in California

Fig: 15

8.2-Se dime ntary Bas in

Clas s ific ation

• Many different basin classification

schemes have been proposed, as

geological thought has evolved from the

ge o s ync line c once pt to plate tectonics

• In the petroleum indus try, a classification

is needed that emphasizes the role of the

s edime ntary bas in as a container for oil

and gas

There are a total of ten bas in type s:

• two that are related to s table continental

plate s ;

• two that develop through plate divergence ;

• four that relate to plate convergence

• two other types , basins that downwarp (Open

& c los e d) into small oceans, form a separate class because of their unique petroleum

features

Basin classification

Fig: 16

Bas in type s and de tails

31

Stable c ontine ntal plate s :

• Interior Bas in

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

Table 10.1 Inte rior Basin (Intracratonic, s ag)

• Dis tinguis hing fe atures simple, single cycle; no uplands; in

continental interiors

• Depos itional His tory mature, shallow water to non-marine

sediments (clastic or carbonate prone); non-depositional or

non-marine late stage

• Res e rvoir equally sandstone or carbonate.

• Source shale.

• Cap shale, less commonly evaporite.

• Trap basement uplift arches and anticlines; combination and

stratigraphic

• Geothe rmal Gradient low to normal.

• Hydrocarbons low S, high gravity crude low natural gas

• Ris ks adequate traps; presence of shale for source and cap.

• Typical Re s erves <0.5- 3 billion bbl hydrocarbon/basin

Foreland basin:

37

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 Fore land Bas in (craton margin, compos ite )

• Dis tinguis hing fe atures multicycle basin on craton edge with

adjacent uplift

• Depos itional His tory 1st cycle mature platform sediments;

unconformity; 2nd cycle orogenic clastics

• Res e rvoir 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

• Geothe rmal Gradient low to above average.

• Hydrocarbons mixed crude, similar to interior basins in 1t

cycle; above average deep thermal gas

• Ris ks trap efficiency; reservoir, source and seal development.

• Typical Re s erves <0.5- 5 billion bbl hydrocarbon/basin

Rift Bas in;

Pull-Apart Bas in (pas s ive

margin, dive rge nt margin);

• Plate divergence:

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

The CuuLong basin of Vietnam

• Table 10.3 Rift Bas in

• Dis tinguis hing fe atures downdropped graben over

continental crust; dormant divergence

• Depos itional His tory 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)

• Res e rvoir 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

• Geothe rmal Gradient normal to high.

• Hydrocarbons highly facies-dependent(paraffinic with

sandstone's; aromatic with carbonates); low to average gas

• Ris ks small trap size; too high gradient; source shale

development

• Typical Re s erves <0.5- 30 billion bbl hydrocarbon/basin

Rift Bas in;

Pull-Apart Bas in (pas s ive

margin, dive rge nt margin);

• Plate divergence:

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, dive rgent margin)

• Dis tinguis hing fe atures coastal half-grabens down-faulted

seaward; intermediate crust; result of ocean-floor spreading

• Depos itional His tory non-marine rift stage sediments;

restricted facies (carbonates, evaporites, black shale) in early separation; prograding clastic wedge in late separation stage

• Res e rvoir 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

• Geothe rmal Gradient below average in marine stages.

• Hydrocarbons rift stage has paraffinic, intermediate gravity

crude; more aromatic, light gravity in separation stage; gas prone

• Ris ks kerogen maturation; biodegradation; pre-separation

source shales; post-separation reservoirs

• Typical Re s erves 2-3 billion bbl hydrocarbon/basin

Fore -Arc

Bac k-Arc

Non-Arc

Collis ion Bas ins

Conve rge nt Margin Bas ins :

• There are two types of basins that are found near

subduction zones that have developed island-arcs

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

• 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, arc basins are found in front of the island-arc Both types run parallel to the trench-arc

fore-system, where the northward-moving

Australian plate is being overridden by

Eurasia

Basins and te ctonic e le me nts of Indone sia

Fig: 35

•A cross section through the Sumatra back-arc and

Mentawai fore-arc basins illustrates the facies and

petroleum habitat

•The Sumatra bas in 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 bas in

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

Fore -Arc

Bac k-Arc

Non-Arc

Collis ion Bas ins

Conve rge nt Margin Bas ins :

• Non-arc bas ins are formed along convergent

margins where the plates move by transcurrent

faulting

• Consequently, they are sometimes called strike-slip

basins The y are also calle d 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

Bac k-Arc Non-Arc Collis ion Bas ins

Conve rge nt Margin Bas ins :

• Collis ion bas ins , 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 basinFig: 41

Fig: 42

Table 10.5 Conve rge nt Margin Basins

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

D collision (median, intermontane, successor)

• Dis tinguis hing features small, deep, young; local extension and

strike slip in regional compression along convergent plate margins.

• Depos itional His tory immature, poorly sorted clastic sediments;

rapidly intertonguing facies; shallow to deep and/or volcanistic.

• Res ervoir 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

• Ris ks maturation; leakage; deformation too intense; igneous

activity; poor reservoir properties.

• Typical Res erves <0.5- 12 billion bbl hydrocarbon/basin

Downwarp Bas in

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

- Tro ugh- related to foreland basins

Idealizaed pattern of a downwarp basin

Fig: 43

Majo r do wnwarp bas ins o f the wo rld

Fig: 45

Generalized cross-section through the Gulf Coast basin, S outhe rn

US A and Gulf of Mexico

Fig: 46

Generalized cross-section through the Arabian-Iranian basin

Fig: 47

Table 10.6 Downwarp Basin

A Ope n- related to pull-apart, passive margins

B Clo s e d- related to foreland basins

C Tro ugh- related to foreland basins

• Dis tinguis hing fe ature s basement and depositional downwarp dipping

into small oceans, inland seas or linear suture zones; intermediate crust.

• De po s itional His tory mixed, interfingering shallow marine facies, either

• Cap mostly shale; both shale and evaporites in B.

• Trap anticlines; salt flow; combination; reefs, pinch-outs and

unconformities.

• Ge othe rmal Gradie nt normal to above average.

• Hydro carbo ns intermediate to mixed gravity crudes; sandstones more

paraffinic, carbonates more aromatic; average to high natural gas.

• Ris ks maturation; leakage; deformation too intense; igneous activity; poor

reservoir properties.

• Typical Re s e rve s 4- 40 billion bbl hydrocarbon/basin (A); 10- >50 (B), 5-

3 (C)