Non-Darcy flow and stress coupling mechanism of fault rocks: Effect of gas compression

Abstract

This study aimed to analyze the evolution of the porosity and permeability of fault rocks under non-Darcy flow-stress coupling. The permeability of broken coal, mudstone, and sandstone with different particle size gradations under different stresses was investigated using an experimental system for the permeability evolution of broken rocks. Experimental results show that broken coal exhibits the best compressibility, followed by broken mudstone, and broken sandstone presents the worst compressibility. The porosity and permeability of the broken rocks decrease rapidly with the increase in confining pressure and then decrease slowly until they stabilize. The crushing of large particles into fine particles under stress is the main reason behind the decreasing porosity and permeability of mixed broken rocks. The smaller the fractal dimension of the particle size gradation during loading, the more serious the particle breakage, the greater the mass loss of large particles, and the greater the decrease in porosity and permeability.