Analysis of stress-dependent permeability in nonorthogonal flow and deformation fields

The stress-dependent permeability of porous-fractured media is examined whe re principal stresses do not coincide with the principal permeabilities. Th is condition is the norm; and may arise when either flow is controlled at t he local level due to the presence of inclined bedding partings or oblique fractures, or as a result of the evolving loading environment. Permeability response is controlled by shear and normal stiffnesses of fractures, frict ional dilation coefficients, skeletal and grain modulii, initial permeabili ties and stress state. For parameters representative of intact and fracture d rocks, hydrostatic loading modes are shown to have the greatest effect in the pre-failure regime. Sheer dilation effects are small, primarily contro lled by the selected magnitudes of shear stiffnesses and dilation coefficie nts. The resulting stress-permeability relationships, which cover both frac tured and intact media, are examined in a numerical study of fluid flow inj ected across the diameter of a cylindrical core with inclined fabric, subje cted to various loading configurations. This is used to produce relationshi ps that allow one to reduce flow test data in non-standard specimen geometr ies, where effective stress changes are simultaneously applied. These resul ts confirm the significant impact of inclination of the rock fabric with re spect to both flow and loading geometry on the evolving permeability field.