Thermo-hydro-mechanical coupled simulation of fracture propagation under cyclic loading in hot dry rockOA

Cyclic-loading hydraulic fracturing generates alternating stresses and complex fracture networks in hot dry rock(HDR),but the predictive accuracy of existing models is limited by insufficient consideration of rock property degradation under cyclic loading.This study introduces an equivalent damage evolution equation to characterize the degradation of elastic modulus,permeability,specific heat capacity,and thermal conductivity,and establishes a thermal-hydro-mechanical(THM)coupled model for cyclic-loading hydraulic fracturing in HDR to simulate fracture initiation and propagation.The results show that under the cyclic hydraulic fracturing conditions examined,(1)When the natural fracture density reaches 0.006 fractures/m^(2),the total fracture length and damaged area increase by 6.63%and 9.44%,respectively.(2)Moderately reducing fracturing fluid viscosity effectively activates natural fractures.For example,a decrease in viscosity from 15 mPa·s to 5 mPa·s results in a 12.70%increase in fracture length and a 9.91%increase in damaged area.(3)A cycle period of 20–40 min/cycle is favorable for fracture network expansion,increasing the damaged area by 9.01%–19.59%and extending the fracture length by up to 21.65%.(4)Increasing the circulation flow rate from 10 m^(3)/min to 16 m^(3)/min accelerates wellbore pressurization,resulting in a 9.31%increase in fracture propagation distance and a 14.05%increase in damaged area.The proposed model effectively characterizes rock property degradation induced by cyclic loading and fracture evolution in HDR,providing theoretical support for optimizing cyclic hydraulic fracturing parameters and enhancing complex fracture network development.