Numerical Simulation of Hydraulic Fracture Propagation in Hot Dry Rock ( <scp>HDR</scp> ) Reservoirs Based on Phase Field Method

ABSTRACT Hydraulic fracturing is an important technology for exploiting hot dry rock (HDR) resources. The efficiency of geothermal resource exploitation is affected by the shape of artificial fractures. A thermal–hydraulic‐mechanical (THM) coupling model was established based on the phase field method to study fracture propagation in HDR reservoirs. A quasi‐monolithic scheme was used to solve displacements and phase field variables, while partitioned schemes were employed to solve temperature and fluid pressure. The adaptive mesh refinement and adaptive timestep control method were introduced to balance computational accuracy and cost. The effects of temperature, pump rate and natural fractures on hydraulic fracture propagation were analysed with the proposed model. The results showed that: The phase field fracture model judges the fracture growth only with the principle of energy minimisation, which can be used to study the hydraulic fracture propagation in HDR reservoirs. The hydraulic fractures in HDR reservoirs are driven by pressure and thermal stress. The thermal effect would change with the temperature difference and pump rate. Natural fractures would affect the direction of hydraulic fractures. We believe that the proposed model can help engineers understand the fracture propagation in HDR reservoirs better.