A fully coupled geomechanical-fluid flow model for shale gas considering desorption hysteresis

Shale gas desorption occurs during development, and it is usually treated as the reverse process of adsorption. However, a large number of experiments have confirmed that there is hysteresis between desorption and adsorption, making it inaccurate to use adsorption effects to study the seepage laws of shale gas. Therefore, desorption characteristics are clarified through molecular simulation, and then a shale gas desorption model is established under different temperatures and pressures. Considering the influence of desorption on solid deformation and gas flow, a coupled geomechanical-fluid flow model is proposed. The multiscale flow mechanisms of shale gas are simulated by finite element method, and the effects of desorption on gas flow and production are evaluated. Combined with statistical methods, a weight evaluation system is proposed to analyze the main controlling factors comprehensively. The results show that desorption capacity is positively correlated with pressure and negatively correlated with temperature, while the degree of desorption hysteresis weakens as the temperature rises. Desorption hysteresis delays the desorption of adsorbed gas, and the actual utilization degree of adsorbed gas decreases during production, thus ignoring desorption effect overestimates shale gas well production. In addition, shale gas production is negatively correlated with stress sensitivity of hydraulic fractures and interlaced distance of hydraulic fractures. It is identified that the main controlling factors for EUR are fracturing parameters, followed by geological factors.