Heat extraction mechanism in hot dry rock based on horizontal wells with multi-stage fracturing

Multi-stage fracturing with horizontal wells is currently recognized as the most promising reservoir stimulation technique for the development of Hot Dry Rock (HDR) resources. While current research predominantly focuses on optimizing operational parameters during injection and extraction, the specific influence of fracture parameters remains underexplored. Experimental evidence confirms that shear-induced dilation significantly impacts reservoir permeability. Consequently, this study establishes a Thermo-Hydro-Mechanical (THM) coupled model based on Discrete Fracture Networks (DFN) to quantitatively characterize network connectivity and investigate the dynamic evolution of fracture apertures driven by shear dilation in multi-stage fractured horizontal wells. A comprehensive sensitivity analysis is conducted to evaluate the impact of fracture morphological parameters and operational parameters on heat extraction performance. Results indicate that rock deformation is predominantly localized around the injection well, while stress perturbations attenuate continuously toward the production well. Notably, fractures with larger strike angles exhibit significant aperture expansion induced by shear dilation, a phenomenon further amplified by increased in-situ stress differences. Crucially, the sensitivity analysis reveals that heat extraction performance exhibits significantly higher sensitivity to fracture morphological parameters than to operational parameters. Consequently, optimizing multi-stage fracturing configurations is identified as a key strategy to mitigate thermal breakthrough. These findings offer essential theoretical guidance for developing efficient heat extraction strategies in HDR reservoirs.