Coupling between the statistical damage model and permeability variation in reservoir sandstone: Theoretical analysis and verification

Reservoir sandstone contains pre-existing weaknesses, and its fluid flow properties may be altered when subjected to mechanical loading. Simulation of the complete deformation process of reservoir sandstone and its fluid transportation is important in the fields of rock mechanics and gas production. Based on the statistical damage theory with consideration of void volume changes and fluid pressure, a new constitutive model was developed to describe the mechanical characteristics of saturated porous media in geo-materials. On the basis of the Weibull distribution for rock micro-strength, the damage variable was defined and a semi-analytical permeability variation model was established. Experimental results demonstrated that the theoretical model was in good agreement with the test data during rock deformation, and the permeability variation is a function of the stress-induced damage. Furthermore, the applicability of the rock failure criterion based on the Drucker-Prager criterion and the energy release principle is discussed. Visible influences of void volume change and fluid pressure in the damage variable calculation were also detected.