Effects of Formation and Injection Parameters on Multi-Field Damage Evolution of Hot Dry Rock During CO2 Fracturing

Low-temperature CO2 fracturing generates obvious thermal tensile disturbance via reservoir–fluid temperature difference, which is an efficient stimulation technology for hot dry rock (HDR). In this work, a two-dimensional plane-strain thermo-hydro-mechanical-damage (THMD) coupling numerical model considering granite mechanical heterogeneity is established, and seven single-variable simulation cases are designed to quantitatively analyze the joint effects of fluid type, reservoir temperature, injection parameters, and in situ stress on HDR damage, temperature-pore pressure field, and system energy evolution. The results show that the damaged area induced by CO2 injection is five times larger than that of water under identical baseline conditions. Raising reservoir temperature or injection pressure significantly strengthens thermo-seepage coupling effects, with the maximum damaged area ratio increased by over 220%. Higher CO2 injection pressure and lower injection temperature weaken thermal stress and restrain fracture propagation; an anisotropic stress field only produces a single main fracture without complex branch networks. Energy analysis indicates injection pressure dominates the accumulation of HDR strain potential energy, and the potential energy under high injection pressure can reach more than 11 times the baseline value. This study quantitatively analyzes the individual influences of fluid type, reservoir temperature, injection temperature, injection pressure, and in situ stress anisotropy on HDR damage evolution, and discusses their combined effects.