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

Abstract

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 × 10¹⁶ J. Moreover, the system demonstrates significant energy-saving and emission-reduction benefits, being capable of saving 9.71 × 10⁸ kg of coal and reducing 2.38 × 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.