Fluid–solid coupling productivity analysis of multi-stage fractured horizontal wells in shale reservoirs

Starting from the micro/macro dynamics of seepage behavior, stress-sensitive experiments are conducted to investigate the fluid–solid coupling and fluid flow law in shale gas reservoirs. These experiments elucidate the interaction between micro and macroscopic effective stress based on the dynamic behavior of seepage. By applying the principle of effective stress, a nonlinear seepage mathematical model for matrix–fracture porosity and permeability in shale reservoirs is established, considering multi-scale fluid–solid coupling effects such as slip diffusion, desorption, gas flow, and shale deformation. Based on the multi-zone coupled seepage physical model of a shale gas reservoir, a fluid–solid coupling productivity model for shale gas horizontal wells is established. This model considers the impact of reservoir deformation on shale matrix–fracture porosity and permeability. Additionally, it reveals the nonlinear seepage law of multistage fractured horizontal wells and analyzes factors influencing productivity. Stress sensitivity experiments on matrix rock samples and fracture rock samples indicate that the stress sensitivity of matrix rock samples is stronger than that of fracture rock samples. The research shows that cumulative gas production, accounting for the influence of fluid–solid coupling on shale gas seepage, differs by approximately 14% compared to when it is not considered. The difference is mainly attributed to the fluid–solid coupling in the fracture network of the reconstruction area. Analyzing fluid–solid coupling parameters reveals that larger elastic modulus results in stronger resistance to deformation, leading to a weaker fluid–solid coupling effect and decreased gas production. Shale skeleton shrinkage deformation during desorption makes the fluid–solid coupling effect more pronounced, though it slightly reduces gas production. Higher Poisson’s ratio and Biot coefficient increase the deformation sensitivity of the shale reservoir and decrease the resistance to deformation in the fracture network zone, resulting in a more significant fluid–solid coupling effect and decreased gas production. As initial porosity increases, the absolute value of the fluid–solid coupling stress sensitivity coefficient decreases gradually, significantly enhancing the fluid–solid coupling effect characterized by the permeability model. The simulation results of the model align with actual field data, showing that gas production follows an “L-shaped” decline pattern with a coincidence rate exceeding 70%, verifying the model’s accuracy.