Faults and joints

Classified in Geology

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Fault Trap
The faulting of stratified rock occurs as a result of Vertical and horizontal stress.  At some Point the rock layers break, resulting in the rock faces along the fracture Moving or slipping past each other into an offset position. A fault trap is Formed when the faulted formations are tilted toward the vertical.  When a non-porous rock face is moved into a Position above and opposite a porous rock face, it seals off the natural flow Of the hydrocarbons allowing them to accumulate.Types of Fault Traps:
a) Normal faults

b) Strike-slip faults
c) Thrust faults
d) Growth faults 
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Faults are in many cases not just associated with structural traps, but They actually generate them, directly or indirectly.  Shown are typical examples from regions where They are the dominant trap type.
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2- Stratigraphic Traps:
Stratigraphic traps are are caused by depositional differences between Adjacent rock types. And formed as a result of differences or variations Between or within stratified rock layers, creating a change or loss of Permeability from one area to another.  These traps do not occur as a result of movement of the strata.Two main Groups can be recognized:
Primary stratigraphic traps result from variations in facies that Developed during sedimentation. These include features such as lenses, Pinch-outs, and appropriate facies changes.
Secondary stratigraphic traps Result from variations that developed after sedimentation, mainly because of Diagenesis.  These include variations due To porosity enhancement by dissolution or loss by cementation.
Lenticular trap:
A porous area surrounded by non-porous strata.  They may be formed from ancient buried river Sand bars, beaches, etc.
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Pinch-out or lateral graded trap:
A trap created by lateral differential deposition when the environmental Deposition changes up-dip.
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Types of Unconformities:
Disconformity
An unconformity in which the beds above and below are parallel
Angular Unconformity
An unconformity in which the older bed intersect the younger beds at an Angle
Nonconformity
An Unconformity in which younger sedimentary rocks overlie older metamorphic or Intrusive igneous rocks


Angular Unconformtiy Trap:
An angular unconformity is one in which older strata dips at an angle Different from that of younger strata.
An angular unconformity trap occurs when inclined, older petroleum Bearing rocks are subjected to the forces of younger non-porous Formations.  This condition may occur Whenever an anticline, dome or monocline are eroded and then overlain with Younger, less permeable strata.
3- Combination Traps:
Many traps result from both of these factors (strati-structural or Combination traps).  A common example is stratigraphic Pinch-out (e.G., a sandstone lens wedging into mudstone) that is combined with Tectonic tilting (which allows hydrocarbons to pond in the up-dip part of the Sandstone wedge).  Other traps result Mainly from fracturing (which creates the reservoir porosity) or hydrodynamic Processes.

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