Numerical Simulation Study of a Novel Horizontally Layered Enhanced Geothermal System: A Case Study of the Qiabuqia Geothermal Area, Qinghai Province, China

Hot dry rock, as a renewable and sustainable energy source, can alleviate resource shortages and environmental pollution. Based on data from the Qiabuqia geothermal field and an established thermal-hydrological-mechanical coupled mathematical model, a novel horizontally layered enhanced geothermal system(EGS) is proposed and compared with the conventional double vertical well EGS. Under the simulated conditions in this paper, the comprehensive heat recovery performance of the horizontally layered EGS is significantly better than that of the double vertical well EGS. Specifically, although the average production temperature of the double vertical well EGS is higher than that of the horizontally layered EGS in the attenuation stage, the heat power output of the horizontally layered EGS ranges from 6.10 MW to 12.25 MW, which is 1.36 to 1.67 times that of the double vertical well EGS. Additionally, the heat recovery rate of the horizontally layered EGS is 6.63% higher than that of the double vertical well EGS and is thus more economical. Finally, parametric analysis was performed to investigate the influence of the controllable parameters on heat recovery for the horizontally layered EGS. The heat power output and heat extraction ratio are proportional to the pressure difference and well spacing and inversely proportional to the injection fluid temperature. The thermal power output is most greatly influenced by the pressure difference, followed by the well spacing and injection fluid temperature. The effects of the pressure difference and well spacing on the heat recovery rate are almost the same, and the injection fluid temperature has no effect.