Investigation on the mechanism of multi-physical field cooperative heat extraction based on Field Synergy Principle

The hot dry rock (HDR) heat extraction process is a typical multi-physical field coupling phenomenon, where efficiency depends not only on the intrinsic properties of individual physical fields but also on their synergistic coordination. To address this, the Field Synergy Principle (FSP) is introduced to analyze the heat extraction process between the HDR reservoir and the working fluid. Based on the coupled temperature-seepage numerical simulation, an evaluation system for heat extraction performance is established, with the Reynolds number, Prandtl number, field synergy number F c , and field synergy angle as key parameters. The mechanism underlying the differential heat extraction performance of various self-supported fracture types is systematically analyzed, and an optimized fracture configuration scheme for enhanced heat extraction is proposed. The results demonstrate that the field synergy effect is significantly stronger at the fracture entrance and in the central region; however, it deteriorates progressively near the fracture wall, where the angle between the velocity vector and temperature gradient is substantially larger. The field synergy number F c of the rough fractures is consistently slightly higher than that of the smooth fractures. This study provides theoretical guidance for the optimized design and efficient development of HDR fracturing reservoirs. • The field synergy principle is introduced to enhance the geothermal heat extraction efficiency. • A heat extraction evaluation system including parameters of Re , Pr , F c and β is established. • The mechanism of enhanced heat transfer in different self-supported fractures is analyzed. • The fracture configuration scheme of enhanced heat extraction is proposed.