Permeability evolution under true triaxial stress conditions of Longmaxi shale in the Sichuan Basin, Southwest China

Abstract

Abstract Shale permeability is considered the critical parameter for commercial gas production. In this work, we investigated the permeability evolution under true triaxial stress conditions of Longmaxi shale. The results showed that shale permeability decreased significantly with increasing intermediate principal stress σ2 and increased gradually with decreasing σ2. And permeability was larger when σ2 was perpendicular to the bedding than that when σ2 was parallel to the bedding. A theoretical model was derived to describe the permeability of shale with respect to effective stress and the results agreed well with the experiment. The matching results showed that the fracture was compressed more easily when σ2 was perpendicular to the bedding and the shale sample was generally compressed in the loading process while swelled during the unloading process. Strong hysteresis was observed for both permeability and strain results. It also warrants testing other gas shales to specifically determine this effect.