Temporal-Spatial Evolution Mechanisms and Optimization Strategies of Heat Transfer in Deep Carbonate Geothermal Reservoirs under Multi-Physics Coupling: A Case Study of the D22 Well in the Xiongan New Area, China

The efficient development of deep carbonate geothermal reservoirs faces complex challenges arising from multi-physics thermal-hydraulic-mechanical-chemical (THMC) coupling interactions. This study establishes a COMSOL-based THMC model using geological data from the deep geothermal system in the Xiongan New Area. We systematically examine the synergistic effects of fracture aperture, injection/production rates, and chemical precipitation on reservoir performance. Numerical simulations reveal three key findings: (1) Heat transfer efficiency increases significantly with fracture apertures > 2 mm but declines beyond 3 mm due to reduced connectivity; (2) CaCO₃ precipitation causes an annual permeability attenuation of 2.1%, while cyclic acid injection (pH 4–5, five-year intervals) reduces cumulative permeability loss by 9.2%; (3) Optimal injection rates of 30–50 kg/s yield minimal levelized energy costs (0.09/kWh)and maximum net present value($19.5 million). This study contributes to the geothermal modeling field by providing a strongly coupled THMC framework that integrates geochemical feedback and economic evaluation to optimize fracture engineering strategies for deep carbonate reservoirs.