Study on multi-field coupled numerical simulation of novel hydrothermal phase change fracturing technology

The new hydrothermal phase change fracturing technology generates high-temperature and high-pressure fluids and instantly releases fractured coal rock bodies, which have good prospects for application in traditional and emerging resource extraction fields. A true triaxial hydrothermal phase change fracturing test and multi-field coupled numerical simulation were designed. The coupled heat-fluid-solid damage model was constructed by COMSOL software, and the change of fluid temperature and pressure, and the damage expansion characteristics of coal rock during the hydrothermal phase change fracturing process were analyzed based on the isentropic expansion theory of fluid. The main research results were: 1. Fracture length increased, and fractal dimension increased with increasing release pressure in different release pressure cases. 2. The damage fractures obtained from the hydrothermal phase change fracturing simulation were distributed along the radial direction, forming four obvious damage zones, and several shorter radial fractures existed near the drill holes. 3. The greater the power of the heat source, the greater the pressure peak, the earlier the damage occurs, when the power of the heat source reaches 6 × 108 W/m3, the rate of temperature rise is maximum, and reaches 450 K in about 10 s. 4. According to the first law of thermodynamics to analyze the adiabatic conditions of the fluid pressure relief would occur after the expansion of the fluid expansion volume increased, the length of the cracks on the surface of the specimen added.