Numerical simulation on the fracture propagation laws of CO₂ fracturing in tight reservoirs

CO₂ fracturing is advantageous in saving water resources and reducing reservoir damage, and its field application effect is good. In order to figure out the fracture propagation laws of CO₂ fracturing, the thermo-hydro-mechanical coupling model for simulating the fracture propagation of CO₂ fracturing was established on the basis of fluid flowing, thermal conduction and solid mechanics equation. Then, this model was solved by means of finite element method and compared with the analytical solution to verify its reliability. Finally, parameter sensitivity analysis was conducted on the fracture propagation of CO₂ fracturing by using the numerical model. It is indicated that the pressure increasing rate is lower before formation fracturing, the fracture length and width are short and the CO₂ filtration rate is higher in the formation whose permeability is higher than 0.01 mD. CO₂ viscosity has significant effect on pressure diffusion and fracture geometry. Injection rate has less effect on the initial pressure, but it can change the pressure increasing rate and extension pressure before formation fracturing. Thermal stress is one of the fracture creating mechanisms of CO₂ fracturing. The larger the temperature difference between the formation and the injected liquid is, the higher the thermal stress is, the lower the initial pressure is and the more easily the fractures extend. The research results can be used as the reference for the design of CO₂ dry fracturing.