Fracture Propagation in Shale and Its Impacts on Shale Gas Production Under Thermal–Fluid–Mechanical Coupling Environments

Shale gas reservoirs can develop extensive fracture networks via hydraulic fracturing. Nevertheless, gas stored in matrix pores remains hard to produce efficiently. Thermal stimulation helps trigger secondary fracture growth inside the matrix and forms multiscale gas-water flow channels to improve reservoir productivity. In this study, a thermo–hydro–mechanical (THM) model is established using COMSOL Multiphysics. The model accounts for fluid seepage, heat transfer, mechanical deformation, and fracture evolution, and assesses shale gas productivity under combined hydraulic fracturing and thermal injection. The effects of initial permeability, injection pressure, and in situ stress on fracture propagation are investigated. Three heating strategies are considered: preheating, heating during fracturing, and continuous heating throughout production. Simulations reveal that thermal injection improves displacement, permeability, and porosity around injection locations. Continuous heating achieves the most obvious fracture expansion. After 6000 days, the daily gas production of the three schemes reaches 50.6839, 73.2167, and 81.403 million m3/d, corresponding to production increases of 44.5% and 60.6%.