Study on the Effect of In-situ Stress on Rock Breaking by High Temperature and High Pressure CO₂ Thermal Shock

In view of the problem of fracturing and increasing permeability in deep reservoirs, the high-temperature and high-pressure CO₂ thermal shock fracturing technology has shown great development potential with its green and low carbon, high rock breaking efficiency and low vibration noise characteristics. On the basis of considering the combustion of heat source, heat and mass transfer, transient nonlinear flow and rock damage evolution process, the heat source power is defined by the energy release equation based on the concentration change derived from the experimental phenomena, so as to establish the corresponding numerical model of high-temperature and high-pressure CO₂ thermal shock rock breaking, analyses the influence of rock confining pressure and in-situ stress difference field on the crack propagation law of thermal shock fracturing, and reveal the complex fracture formation mechanism. The results show that: The high-temperature and high-pressure CO₂ thermal shock fracturing process is mainly composed of two stages, namely the dynamic fracturing stage under the action of supercritical CO₂ impact force and the quasi-static stage of high-energy CO₂ gas-driven fracture expansion. The initial in-situ stress can inhibit the expansion of radial fractures within the rock under the impact force to a certain extent. The peak fluid pressure and rock fracturing pressure tend to decrease with the increase of the initial in-situ stress difference, and the peak fluid pressure increases with the increase of rock confining pressure.