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Petroleum Geology > Traps > Flashcards

Traps Flashcards

1
Q

Stratigraphic Trap

A

a trap that is the result of lateral variation in the lithology of the reservoir rock, or a break in continuity.

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2
Q

Formation of Stratigraphic Traps

A

formed by any variation in the stratigraphy that is independent of structural deformation, except for regional tilting

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3
Q

Depositional Stratigraphic Traps

A

variations in porosity and/or permeability due to changes in facies

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4
Q

Diagenetic Stratigraphic Traps

A

diagenetic alteration (such as dolomitization of a limestone)

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5
Q

Erosional Stratigraphic Traps

A

truncation of a permeable rock by an unconformity and overlapping by impermeable rocks

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6
Q

Formation of Primary Stratigraphic Traps

A

formed during deposition and/or lithification, and are a direct product of the depositional environment

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7
Q

Lense Trap

A

a thin, lenticular body of porous and permeable clastic rock enlcosed in impermeable sediments

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8
Q

Facies Change:

A

lateral gradation within a formation or group of rocks resulting from a contemporaneous deposition of sediments of differing character (sandstone grades into a shale laterally)

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9
Q

Depositional Pinchout Traps

A

wedge-out traps; feather-edge traps;occur whnever there is a progressive lateral (updip) diminution of reservoir bed thickness

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10
Q

Shoestring-Sand Traps

A

long, narrow sand deposits, up to 3/4 of a mile wide and many miles in length surrounded by impermeable clays and shales

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11
Q

Porous Carbonate Facies

A

pourous facies enclosed in or terminated by normal impermeableshales, limestones, and dolostones, and nearly tabular lenses composed of organisms called biostromes

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12
Q

Porous Mound

A

lens-shaped carbonate build-ups consisting mostly of organisms and surrounded by impermeable rocks, called organic reefs or bioherms

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13
Q

Unconformity:

A

a break in the geologic sequence due to erosion or a period of non-deposition, resulting in a hiatus, or time gap in the rock record

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14
Q

Disconformity

A

where the beds above and below the unconformity surface are not parallel but meet at an angle

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15
Q

Non-Conformity

A

where sedimentary layers are juxtaposed to igneous rocks

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16
Q

Buttress Unconformity

A

usually a type of angular unconformity, where the beds overlying the unconformity surface on-lap the unconformity surface

17
Q

Diagenetic Traps:

A

occur when a lateral recudtion in porisity has a significant effect upon capillary entry pressure, so that the movement of petroleum is arrested. These variations may be due to facies changes, although in this trap type diagenesis and/or solution effect are the principal controlling process

18
Q

Structural Traps

A

the trap is formed in a reservoir rock as a result of folding and/or faulting.

19
Q

Structural Closure

A

the vertical distance from the highest point down to the lowest closed contour

20
Q

Structural Relief

A

the height to which a folded bed rises above the regional slope, usually greater than the structural closure

21
Q

Reservoir Volume

A

effective pore space between the underlying water table and overlying roof rock

22
Q

Oil and Gas Column

A

the vertical distance from the oil/water or gas/water contact to the highest point in the trap

23
Q

Changes of the Shape of a Structural Trap with Depth

A

the shape of the fold may change with depth

24
Q

Changes of the Size of a Structural Trap with Depth

A

the size of the fold usually changes with depth, commonly intensifying

25
Q

Changes of the Amplitude of a Structural Trap with Depth

A

the distance from crest or trough to midpoint, may increase or decrease with depth

26
Q

Changes of the Position of the Crest of a Structural Trap with Depth

A

will migrate with depth if the fold is not perfectly upright (upright means the hinge plane is vertical)

27
Q

Causes of Buckle Folds/Flexural Folds

A

horizontal compression or layer-parallel compression

28
Q

Causes of Metamorphic Deformations

A

shear stresses; the folds are usually asymmetrical

29
Q

Causes of Drag Folding

A

frictional drag along faults

30
Q

Causes of Drape Folding

A

usually created by basement uplifts, layers above basement are passively folded

31
Q

Causes of Diapiric Folding

A

Salt domes; layers above rising diapirs are passively folded

32
Q

Combination Traps

A

traps that combine structural, stratigraphic, and fluid barriers in varying proportions

33
Q

Salt Dome Traps

A

The intrusion of deep-seated rock salt into the overlying sediments may form a great
variety of traps, structural, stratigraphic, and combination. Most productive salt dome traps are
located in the Gulf Coastal region of the US, northern Germany, the North Sea, and the Emba
region of Kazakhstan (north of the Caspian Sea). Many other areas contain unproductive salt
domes.

34
Q

Trap

A

the mechanism that places the seal on the reservoir

Petroleum Geology (5 decks)

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