Permeability Estimation From Velocity Anisotropy In Fractured Rock

Abstract

Cracks in a rock mass subjected to a uniaxial stress will be preferentially closed depending on the angle between the fracture normal and the direction of the applied stress. If the prestress fracture distribution is isotropic, the effective elastic properties of such a material are then transversely isotropic due to the preferred alignment of the cracks. Velocity measurements in multiple directions are used to invert for the probability density function describing orientations of crack normals in such a rock. We suggest a means of using the results on fracture distribution from the velocity inversion to estimate the anisotropic permeability of the fracture system. This approach yields a prediction of permeability as a function of the angle from the uniaxial stress direction.