Numerical investigation of the influence of fracture morphology on Enhanced Geothermal System (EGS) development using the Discrete Element Method

• 1. Fluid pressure, thermal stress, and thermal expansion of the rock matrix are incorporated. • 2. Neglecting rock deformation may overestimate temperature and raise project costs. • 3. Multi-cluster hydraulic fracturing technology can enhance the efficiency of EGS development.. The available hot dry rock resources in the Earth’s crust were estimated to be approximately 30 times greater than the total reserves of oil, natural gas, and coal, highlighting their significant development potential. Enhanced Geothermal Systems (EGS) created artificial fractures to facilitate fluid flow and heat exchange, thereby offering higher extraction efficiency compared to conventional geothermal reservoirs. However, most existing studies assume fixed deformation of artificial fractures, which deviates significantly from actual geothermal reservoir conditions and fails to capture the complex interactions inherent in a fully coupled thermo-hydro-mechanical (THM) process. To bridge this gap, we developed a fully coupled THM dynamic model for EGS development based on the Discrete Element Method (DEM), which explicitly accounts for fracture deformation, stress evolution, and heat–fluid interactions. The reliability of the model was validated against analytical solutions, demonstrating its capability to accurately simulate the coupled behavior of fractured geothermal systems. The simulation results demonstrated that neglecting the influence of injected fluid on rock deformation led to an overestimation of the production temperature. Increasing fluid viscosity slightly improved EGS efficiency, although the enhancement was limited. A substantial increase in proppant particle size, which widened the fractures, resulted in a slight decrease in production temperature. Higher injection rates lowered the production temperature but significantly increased fluid output, with power generation initially declined and then rose. While increasing the number of fracture clusters enhanced EGS performance, optimizing fracturing strategies and utilizing effective fracture networks proved more effective for geothermal extraction. Furthermore, a high density of natural fractures in the geothermal reservoir markedly improved EGS efficiency. In a homogeneous reservoir, the addition of 100, 200, and 400 natural fractures increased the production temperature by 9.9 °C, 46.1 °C, and 114.2 °C, respectively.