Experimental study on the evolution of seepage characteristics in shale fractures under confining pressure and temperature conditions

Understanding and investigating the gas transport mechanisms in shale fractures is crucial for ensuring the safe operation of various underground engineering activities. In this study, experimental investigations were conducted on shale fractures with different matching degrees to examine their deformation and seepage characteristics under different confining pressures and temperatures. The results demonstrate that the permeability coefficient continuously decreases with increasing confining pressure and temperature, while the GBP shows a continuous increase. Notably, both parameters exhibit a higher rate of change during the initial stage of pressure application, which gradually slows down thereafter. Significant differences were observed in the seepage characteristics between fractures with different matching degrees. The flow rate in poorly matched fractures (S1) was approximately three times higher than that in well-matched fractures (S2), while the GBP of S1 was only about half of S2. This indicates that the matching degree not only affects the initial aperture of fractures but also influences their deformation behavior. Specifically, fractures with lower matching degrees (S1) exhibited larger initial apertures compared to well-matched fractures (S2). Under confining pressure, the primary deformation mechanism in poorly matched fractures was shear failure, whereas well-matched fractures predominantly underwent plastic deformation.