Anisotropic flow characteristics in single-fractured tensile and shear fractures of granite subjected to various confining stress

Anisotropic flow characteristics in single-fractured tensile and shear fractures of granite subjected to various confining stress were investigated by experiments and experimental results-based flow simulations. Anisotropic characteristics in aspects like permeability reduction rate, stress dependency of permeability, flow path in fracture and fracture aperture distribution were analyzed and compared between tensile and shear fractures. The main conclusions are as follows: (1) for tensile fracture, k_X is slightly lower than k_Y, the average permeability anisotropic coefficient $α$_k (⁠$α$_k=k_X/k_Y) is in the range of 0.236∼0.779. For shear fracture, k_X is obviously lower than k_Y, $α$_k is in the range of 0.038∼0.163, therefore, the permeability anisotropy in shear fracture is stronger than tensile fracture. (2) Strong channeling effect exists in both shear and tensile fractures. The stress dependence coefficient of permeability is 0.731MPa^-1 in X direction and 0.365MPa^-1 in Y direction for tensile fracture and this data is 0.034 and 0.010MPa^-1 respectively for shear fracture, indicating that the dependency of permeability on stress also shows anisotropic. (3) An empirical model of $α$_kbased on stress and fracture aperture variogram was proposed. Based on $α$_k, permeability along both X and Y directions can be predicted well, especially under relatively high confining stress.