Stress influence on the permeability of a sample heterogeneous rock

In this study, a numerical methodology has been developed and discussed to investigate the influence of in situ stresses, including normal and tractional stresses, on the permeability of a heterogeneous intact rock. Flow properties of a representative rock sample composed of three different rock types, randomly located in a rock block, is studied under different stress regimes. Porosity and permeability within each rock type is distributed using statistical distributions. Different stress regimes corresponding to the rock sample located at surface, and at subsurface with horizontal stresses applied in two different orientations are investigated. The stress distribution in the rock sample under different stress scenarios is calculated and is used to update the permeability and porosity at different locations within the rock sample. The ensemble permeability tensors are calculated by running flow simulations in three perpendicular directions and upscaling the permeability from the element level (5 mm) to the sample scale (5 m). It is demonstrated that the flow properties of the studied heterogeneous rock sample reduce considerably when the sample is taken from the surface to a depth of 1 km. More importantly, it is shown that when the horizontal stresses are not perpendicular to the sidewalls of the rock sample, they create shear stresses which further reduce the permeability.