Pore Structure and Permeability Evolution of Porous Media Under in Situ Stress and Pore Pressure: Discrete Element Method Simulation on Digital Core

Abstract

In stress-sensitive oil and gas reservoirs, formation rock deformation occurs under in situ stress and pore pressure, affecting the rock's porosity and permeability. Pore deformation is the fundamental mechanism. However, the literature on numerical simulation of rock porosity and permeability at the pore scale is rare. In this paper a numerical simulation framework of pore scale is proposed based on the discrete element method. The pore geometry and permeability evolution of the core are quantitatively analyzed by the digital core method. Firstly, the coupled fluid-discrete element method (CFM-DEM) is used to simulate the samples' deformation under different stress and pore pressures. We then reconstruct the digital core using Avizo. Finally, the pore geometric topological structures are analyzed, and the permeability changes are calculated. The results show that stress can reduce porosity, modify pore shape, and lead to poor porosity connectivity and permeability, while pore pressure can weaken such trends.