致密储层CO2压裂裂缝扩展规律数值模拟

CO₂压裂具有节约水资源、降低储层伤害等优点，并已在矿场实践中取得良好效果。为认清CO₂压裂裂缝扩展规律，基于流体流动、热传导和固体力学方程，建立CO₂压裂裂缝扩展热流固耦合模型。采用有限元法求解该模型，并与解析解对比验证模型可靠性。根据数值模型对CO₂压裂裂缝扩展进行参数敏感性分析，结果表明:CO₂在渗透率高于0.01 mD的地层中滤失量较大，地层破裂前增压速率较低，缝长和缝宽较小；CO₂黏度显著影响压力扩散和裂缝几何尺寸；注入排量对起裂压力影响较小，但会改变地层破裂前增压速率和延伸压力；热应力造缝是CO₂压裂造缝机理之一，地层与注入液的温度差越大，热应力越大，地层起裂压力越小，裂缝延伸越容易。研究结果可为CO₂干法压裂设计提供参考。

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.