The Influence of the Interlayer Structure Under the Combined Effect of Temperature and Pressure on the Permeability Law of Shale

The laminated structure in shale rock plays a crucial role in fluid migration during shale gas exploitation. This study investigated the evolution patterns and mechanisms of shale permeability under the influence of laminae through multiple permeability experiments, including steady-state flow tests, confined pressure permeability tests, thermo-hydro-mechanical coupled permeability tests, fracture permeability tests, and fracturing fluid damage experiments. The results show that the permeability of the shale is significantly controlled by the laminated structure. Pores and micro-cracks develop along the laminated structure direction, which is conducive to the formation of seepage channels in vertical laminated specimens, while parallel laminated specimens are affected by multiple laminated structures, resulting in lower permeability. Increasing confining pressure leads to a rapid decrease in permeability, indicating that the closure of fractures is the key factor controlling the permeability characteristics of shale. Increasing temperature causes shale to further increase permeability under the effects of thermal stress, but the enhancement effect is weakened under high confining pressure. Artificial fractures significantly enhance the permeability of shale under low confining pressure, but the closure of artificial fractures reduces the permeability effect under high confining pressure. The effect of fracturing fluid leads to a decrease in shale permeability, and the damage to shale is more significant under high confining pressure.