Stress-induced coupling between anisotropic permeability and shear wave splitting

Abstract

The stress-sensitivity (poro-reactivity) of fluid saturated porous rock leads to effective anisotropy in the permeability of many laboratory experiments and in large-scale field phenomena such as the natural directivity of water-flooding caused by horizontal differential components of the regional stress field (Heffer and Koutsabeloulis 1993). One of the most interesting features of stress-sensitivity of porous rock is the effect of the coupling between stress-induced variations in anisotropic permeability and elastic shear-waves (King et al. 1994) that in principle allows changes in reservoir rock permeability to be monitored with seismic shear waves (Crampin 1994). A previous theoretical consideration of the possible stress-induced coupling between the permeability and elastic waves (Gibson and Toksoz 1990) was restricted to uniaxial stress that seems inappropriate for in situ situations where the horizontal differential stress field and horizontal permeability anisotropy is of primary importance. We present a theoretical model for the coupling between permeability and elastic waves in a triaxial differential stress field and elevated pore-pressure based on the APE model of anisotropic poro-elasticity of Zatsepin and Crampin (1995).