Discrete Element Modeling of Permeability Evolution During Progressive Failure of a Low-Permeable Rock Under Triaxial Compression

Abstract

Understanding permeability evolution caused by the nucleation, propagation and coalescence of cracks enables to better assess fluid migration in the vicinity of underground excavations, boreholes or reservoirs. In this study, we propose a three-dimensional approach combining a bonded particle model and a dual-permeability pore network model to investigate the crack permeability behavior of low-permeable rocks. First, we verify the performances of the numerical scheme by comparing its predictions to analytical permeability solutions for microcracked and fractured porous samples, respectively. Then, we simulate a triaxial compression test on an argillaceous rock sample with periodic permeability measurements. The model is able to reproduce the stress–strain–permeability evolution observed experimentally, from the early stage of microcracking up to the residual post-failure state: (i) permeability does not change significantly before reaching the crack damage threshold and (ii) permeability increases by several orders of magnitude after failure due to the appearance of a discrete shear band across the sample. The good agreement between the numerical results and the experimental observations confirms the relevance of the proposed approach to simulate the crack permeability behavior of low permeable rocks during their progressive failure. Based on this result, we simulate triaxial compression tests under different confining pressures to propose relationships between post-failure permeability and residual mean stress.