Based on the peridynamics method, the bond model was applied to treat the thermal diffusion of rock and the conventional state model was adopt to simulate the displacement evolution. According to the number of broken bonds between material points, the material damage was determined to track real-time fracture propagation. The interaction between water and rock was realized by applying pressure and temperature of water to fracture surface. And a numerical model was proposed to simulate hydraulic fracturing in high-temperature rock considering the thermal-mechanical coupling effect. The accuracy of the proposed model was verified according to the test results of rock heating fracture propagation. Finally, the morphology of hydraulic fracturing-induced rock fractures were discussed considering the effects of water pressure, rock initial temperature and elastic modulus, the sensitivity of each factor to fracture geometry parameters was analyzed based on the comprehensive sensitivity attribute identification method. The results indicate that under conditions of low water pressure or initial rock temperature, the primary fractures exhibit a near-symmetric distribution, and there is almost no fracture branching. With the increase of water pressure or initial temperature, the number of fracture gradually increases and the bifurcation occurs, the total length and fracture aperture also increase. When the mean elastic modulus of rock is small, the fractures are well developed and many tiny cracks appear. With the increase of the average elastic modulus, the number of fracture branches and micro-fractures decreases obviously, and the total length and fracture aperture also decrease accordingly, while the rock fracture initiation time increases approximately linearly. The comprehensive sensitivity evaluation of rock material parameters and environmental parameters shows that rock fracture propagation is highly sensitive to elastic modulus and water pressure, but insensitive to water temperature.

In this study, the rock fracture propagation is simulated based on the ordinary state-based peridynamics, and a numerical model of rock hydraulic fracturing is proposed by means of real-time tracking of newly generated fracture and applying pressure to simulating the interaction between fracturing fluid and fracture surface. According to the digital image processing technology, the Zhang-Suen thinning algorithm is applied to extracting the skeleton of hydraulic fracture network, and a quantitative method of hydraulic fracture network is presented by using the statistical method to calculate the morphological parameters. Finally, the process of hydraulic fracture propagation and the evolution of fracture network morphological parameters are studied considering the effects of loading rate, in situ stress condition and elastic modulus. The results show that when the loading rate is small, the main fracture expands towards the direction of the larger in situ stress, and the fracture branch is not obvious. Increasing the loading rate can increase the average width and density of fractures, promote the opening degree and number of fractures, enhance the complexity of fracture network, and improve its permeability. When the horizontal and vertical in situ stresses are the same, the major fractures intersect. With the increase of vertical in situ stress, the horizontal fractures are restrained, the major fracture propagates along the vertical direction, and the total length and density of fractures increase. The increase of elastic modulus of rock mass can reduce the propagation of fracture branches and simplify the fracture network.