Thermal and hydraulic characteristics of a new proposed flyover-crossing fracture configuration for the enhanced geothermal system

An advanced enhanced geothermal system (EGS) is capable of unlocking many thousands of megawatts of power in hot dry rocks, and the fracture configuration is a critical factor influencing its efficiency. A flyover-crossing fracture (FCF) configuration for EGS was proposed in this paper, to enhance heat transfer between the working fluid and reservoir and thus the productivity of EGS. A 3D transient thermal-hydraulic model was established to analyze the heat extraction of the FCF-EGS, and the effects of intersection angles of the FCF on the heat and mass transfer as well as the productivity of the EGS were examined. The FCF-EGS was found to bring higher production temperature and thermal power output than the conventional double-horizontal-well EGS during a 30-year heat recovery period, and the heat extraction capacity of the FCF-EGS was found to increase with the intersection angle. It was also found that the FCF with a 90°cross-angle has the best heat extraction performance, with the output thermal power increased by 5.12% compared to the conventional double-horizontal-well EGS, due to the enhancement of heat transfer between the working fluid and rock. Although this fracture system requires more investment in fracturing and larger pressure in production, the increase in heat production far outweighs this input. This study provides a novel potential fracture configuration for exploiting HDR geothermal energy.