Fault zone permeability in outcrop is quantified by detailed geologic mapping and by measurements using a minipermeameter. Deformation bands, zones of deformation bands, and slip planes are structural elements associated with successive stages in the evolution of a fault zone in porous sandstones. Deformation bands have a porosity about one order of magnitude less than the surrounding host rock and, on average, a permeability three orders of magnitude less than the surrounding host rock. The intensity of cataclasis and the clay content control the amount of permeability reduction as measured perpendicular to a band. The wall rock in proximity to slip planes can have permeabilities more than seven orders of magnitude less than the pristine sandstone. Capillary pressure within deformation bands is estimated to be 10–100 times larger than that in the surrounding host rock. Thus, deformation bands and slip planes can substantially modify fluid flow properties of a reservoir and have potential sealing capabilities with respect to a nonwetting phase, as evident in outcrop exposure.

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