Experimental and numerical investigation of the failure mechanism and permeability evolution of sandstone based on hydro-mechanical coupling

The exploitation of natural gas and oil in the low-permeability reservoir is a severe challenge in the field of deep underground energy extraction. Therefore, a thorough understanding of the failure mechanism of reservoir sandstone under hydro-mechanical coupling is of great significance. The purpose of this study is to carry out triaxial compression tests of reservoir sandstone under different confining pressures and seepage pressures to investigate the failure mechanism and permeability evolution of reservoir sandstone. Laboratory experimental results show that the permeability of sandstone first decreases to a minimum and then increases with deviatoric stress, and finally reaches the maximum when a macroscopic fracture is formed. In addition, the permeability of sandstone gradually decreases with the increase of effective confining pressure, showing a good exponential function relationship. Axial strain stiffness is proposed to characterize the ability of the rock to resist deformation and failure, and an empirical equation of maximum axial strain stiffness, confining pressure and seepage pressure is established. Subsequently, the failure process of rock is reproduced in COMSOL based on elastic damage mechanics, porous elastic medium theory and the effective stress principle. The failure mechanism and the distribution of seepage pressure of rock feature points under different hydro-mechanical coupling are discussed. As a perfect tool, the distribution of streamline can intuitively reflect the impact of damage on porosity and permeability.