Evaluation of Flow Anisotropy Within a Simulated Shear Fracture Under Stress Conditions from Shallow to Deep Reservoirs

Abstract

We investigate the anisotropy in permeability and the mechanism of formation of permeable zones within a sheared fracture, in artificially/naturally fractured reservoirs. The normal stress conditions were up to 90 MPa corresponding to the overburden pressure at a depth of approximately 3-4 kilometers. Numerical flow simulations were made using numerically generated fracture aperture distributions that are based on contact area (or hydraulically ineffective area) measurements. The results show that 1) the normal stress and shear offset dependencies in fracture permeability, and 2) the anisotropy in fracture permeability occur at higher stress conditions than have previously evaluated. The flow distributions obtained from the simulations show that the normal stress and the shear offset dependencies in permeability can be explained by the same dependencies in preferential flow paths. In addition, the flow distributions also showed that permeability anisotropy resulted from the variation of tortuosity in the preferential paths. The investigation of the contact ratio shows an anisotropy in connectivity of the fracture aperture, thus supporting the consequent variation of the tortuosity. We conclude that the permeability anisotropy caused by the anisotropy in the aperture connectivity might exist, even at depths of 3?4 kilometers.