Traps Flashcards
Stratigraphic Trap
a trap that is the result of lateral variation in the lithology of the reservoir rock, or a break in continuity.
Formation of Stratigraphic Traps
formed by any variation in the stratigraphy that is independent of structural deformation, except for regional tilting
Depositional Stratigraphic Traps
variations in porosity and/or permeability due to changes in facies
Diagenetic Stratigraphic Traps
diagenetic alteration (such as dolomitization of a limestone)
Erosional Stratigraphic Traps
truncation of a permeable rock by an unconformity and overlapping by impermeable rocks
Formation of Primary Stratigraphic Traps
formed during deposition and/or lithification, and are a direct product of the depositional environment
Lense Trap
a thin, lenticular body of porous and permeable clastic rock enlcosed in impermeable sediments
Facies Change:
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)
Depositional Pinchout Traps
wedge-out traps; feather-edge traps;occur whnever there is a progressive lateral (updip) diminution of reservoir bed thickness
Shoestring-Sand Traps
long, narrow sand deposits, up to 3/4 of a mile wide and many miles in length surrounded by impermeable clays and shales
Porous Carbonate Facies
pourous facies enclosed in or terminated by normal impermeableshales, limestones, and dolostones, and nearly tabular lenses composed of organisms called biostromes
Porous Mound
lens-shaped carbonate build-ups consisting mostly of organisms and surrounded by impermeable rocks, called organic reefs or bioherms
Unconformity:
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
Disconformity
where the beds above and below the unconformity surface are not parallel but meet at an angle
Non-Conformity
where sedimentary layers are juxtaposed to igneous rocks
Buttress Unconformity
usually a type of angular unconformity, where the beds overlying the unconformity surface on-lap the unconformity surface
Diagenetic Traps:
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
Structural Traps
the trap is formed in a reservoir rock as a result of folding and/or faulting.
Structural Closure
the vertical distance from the highest point down to the lowest closed contour
Structural Relief
the height to which a folded bed rises above the regional slope, usually greater than the structural closure
Reservoir Volume
effective pore space between the underlying water table and overlying roof rock
Oil and Gas Column
the vertical distance from the oil/water or gas/water contact to the highest point in the trap
Changes of the Shape of a Structural Trap with Depth
the shape of the fold may change with depth
Changes of the Size of a Structural Trap with Depth
the size of the fold usually changes with depth, commonly intensifying
Changes of the Amplitude of a Structural Trap with Depth
the distance from crest or trough to midpoint, may increase or decrease with depth
Changes of the Position of the Crest of a Structural Trap with Depth
will migrate with depth if the fold is not perfectly upright (upright means the hinge plane is vertical)
Causes of Buckle Folds/Flexural Folds
horizontal compression or layer-parallel compression
Causes of Metamorphic Deformations
shear stresses; the folds are usually asymmetrical
Causes of Drag Folding
frictional drag along faults
Causes of Drape Folding
usually created by basement uplifts, layers above basement are passively folded
Causes of Diapiric Folding
Salt domes; layers above rising diapirs are passively folded
Combination Traps
traps that combine structural, stratigraphic, and fluid barriers in varying proportions
Salt Dome Traps
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.
Trap
the mechanism that places the seal on the reservoir
