Production performance of a post-fracturing elastoplastic model for deep shale gas reservoirs

Deep shale gas reservoirs are characterized by high temperature, high pressure, and ultra-low permeability, making them highly susceptible to plastic deformation during hydraulic fracturing. In such cases, conventional elastic models fail to capture the complex post-fracturing rock behavior, highlighting the suitability of elastoplastic modeling. This study develops a fully coupled flow-geomechanics model incorporating elastoplastic deformation to analyze production performance in deep shale gas reservoirs. The proposed model dynamically couples post-fracturing plastic deformation with multiscale gas transport mechanisms, including slip flow, Knudsen diffusion, and surface diffusion. It incorporates governing equations that describe gas migration through the matrix, natural fractures, and hydraulic fractures, while simultaneously accounting for dynamic changes in effective stress, porosity, and permeability. Model validation is performed using the classical Mandel problem, followed by a detailed analysis of key parameters influencing elastoplastic production performance. Simulation results indicate that in elastoplastic reservoirs, production initially increases and then declines with increasing bottom-hole pressure (BHP), while elastic reservoirs show a continuous increase. When the initial reservoir pressure is 50 MPa, elastic production dominates below BHP of 31.5 MPa, whereas elastoplastic production becomes more favorable above this threshold. A critical inflection point emerges when the BHP is approximately 0.5–0.625 times the original formation pressure. Furthermore, the most important influencing factors of elastic and elastoplastic formations are BHP and original formation pressure, respectively. These findings offer valuable insights into optimizing production strategies for deep shale gas reservoirs under complex geomechanical conditions.