Modeling of Stress and Pressure Dependence of the Sealing and Transport Properties of the Fault

Faults (shear cracks) are formed by the coalescence of tensile microcracks in the brittle caprock. The damage zone of the fault consisting of microcracks can serve as a permeable pathway within sealing formations. Like macrofractures, microfractures occur in populations that exhibit well-defined statistical properties such as their size distribution. The are many publications explaining how the aperture size distribution can be related to the sealing and transport properties, described by capillary pressure and effective phase permeabilities, however there are no models which explain how the aperture distribution depends the effective confining stress and on the saturation degree. Available models, developed for porous rock are not applicable to fractured rock, because fracture is much more compressible than the pore throat. In this paper the author proposed a new theoretical model, applied in two steps to the damage zone of the fault. In the first step the author developed new analytical solutions for the effective phase permeabilities and capillary pressure of the rock possessing a single deformable crack. In the second step the author applied the analytical solutions to multi-scale microcrack system of the damage zone of the fault to predict the stress and pressure dependence of the sealing and transport properties of the fault.