Fracture traps
The reason for including fold traps and fault traps in the structural system may be obvious, but the reason for including fracture traps may not. Some might argue that fractures are just another porosity type and should be thought of as part of the reservoir, not as a trap regime. This classification scheme includes fracture traps in the structural system because fractures are a result of deformation and/or displacement and therefore are structural in nature.
Definitions
The following definitions for fracture, fracture reservoir, and fracture trap are used in the classification scheme.
Fracture—Approximately planar surface along which originally contiguous rocks have broken and separated and along which the relative displacement of originally adjacent points across the fracture is small compared with fracture length.[1]
Fracture Reservoir—Reservoir in which most of the permeability and some of the porosity is provided by open fractures.
Fracture Trap—Trap in which lateral boundaries of the trap are provided by change from fractured reservoir to unfractured or less fractured rock or by change from open, permeable fractures to cement-filled or narrow-aperture, low-permeability fractures.
Fracture types
Fractures can be divided into three major groups: extension, shear, and complex.
Extension Fracture—displacement of originally adjacent points across the fracture is perpendicular to the fracture surface. The term “extension” refers only to the opening or extension of the space between the fracture walls, not to the stress system that caused the fracture.
Shear Fracture—displacement of originally adjacent points across the fracture is parallel to the fracture surface.
Complex Fracture—fracture with a complex history of displacement and rejuvenation, and which may have originated as a shear fracture and been rejuvenated as an extension fracture or vice versa.
See also
References
- ↑ Pollard, D. D., and P. Segall, 1987, Theoretical displacements add stresses near fractures with applications to fault, joints, veins, dikes, and solution surfaces, in B. K. Atkinson, ed., Fracture Mechanics of Rock: London, Academic Press, p. 277–349.
External links
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