Intrinsic anisotropy in fracture permeability

Abstract

Contrary to the assumption in cubic law, the surface of fractures has some degree of roughness, which impacts their fluid dynamics. Incorporating the effect of roughness can improve the simulation of fluid flow in fractures and faults, as well as proppant transport in hydraulic fracturing. To investigate the effect of roughness on the fluid flow, we created a fracture using the Brazilian test, and its roughness was measured using a laser profilometer. Experimental permeability measurements showed a reduction in permeability as the effective stress increased. However, the unmatching surfaces of the fracture prevented its complete mechanical closure. Numerical simulations of the fluid dynamics were conducted on the measured fracture geometry. We determined that the hydraulic fracture aperture is less than the mechanical fracture aperture and that there was anisotropy in the fracture permeability. The ratio of hydraulic fracture aperture to mechanical fracture aperture, as well as anisotropy in fracture permeability, increased when the fracture aperture decreased. The anisotropy in fracture permeability was 45% at the lowest simulated fracture aperture. Integrating the experimental and numerical data, we estimated the fracture porosity and fracture permeability.