Comprehensive investigation on the heat extraction performance of a novel enhanced geothermal system based on mining technology

This study proposes a novel enhanced geothermal system based on mining technology (EGS-M) to facilitate commercial exploitation of deep geothermal resources. The system utilizes the high permeability goaf from deep high-temperature mining as the geothermal reservoir, avoiding costly wellbore drilling and fracturing in deep brittle rocks. The numerous goafs in large mines provide ample reservoir volume for large-scale geothermal development. A new 3D transient numerical model based on mining parameters was established to evaluate heat extraction performance. Using this model, a series of simulations were performed to quantitatively investigate the effects of key factors on the heat extraction efficiency and life-span. Simulation results indicate that the influence of borehole depth on heat extraction performance is nonlinear, with optimal performance when boreholes are 0.8 times reservoir height. Using supercritical CO2 instead of water raised production temperature by 46.76 K but decreased output power by 10.38 MW and cumulative heat extraction by 1.44 x 1016 J. Moreover, the system demonstrates significant energy-saving and emission-reduction benefits, being capable of saving 9.71 x 108 kg of coal and reducing 2.38 x 109 kg of CO2 emissions over a 20-year production period. Compared to the Soultz EGS, a leading commercially operated project, the proposed system had 18.7 % higher average production temperature and 36.9 % greater average output power. The EGS-M offers a novel geothermal approach achieving economic efficiency and environmental sustainability by synergistically combining deep mineral extraction with geothermal energy development.