Integrated PD-HT-FEM simulation of fracture networks and heat extraction in enhanced geothermal systems under coupled thermal-hydraulic-mechanical condition

Enhanced geothermal systems (EGS) are an effective approach for exploiting geothermal energy from hot dry rock (HDR). Conducting a comprehensive simulation that encompasses the entire process from EGS hydraulic fracturing to heat extraction by the working fluid, and then outflow through the production well, is an important but numerically challenging task. Although many previous studies thoroughly analyzed the thermal-hydraulic-mechanical (THM) coupling mechanism in fractured rock masses during EGS operation, the considered fracture network geometric models were directly predefined without considering stimulation process. In this paper, combining peridynamics (PD), Hough transform (HT), and finite element method (FEM), we propose an integrated simulation method for the entire process containing hydraulic stimulation and heat extraction during long-term operation. The results indicate that the increases in elastic modulus and thermal expansion coefficient of HDR cause a decrease in the outlet temperature of the production well, an increase in the heat extraction ratio, and an earlier thermal breakthrough. The variations in these indices obtained using the PD-HT-FEM method are significantly greater than those obtained using a same geometry network model. This study provides a method for simulating and predicting EGS operations, highlighting the importance of conducting a comprehensive analysis of the fracturing and heat extraction.