层理页岩水力裂缝扩展规律的相场法研究

Propagation of hydraulic fractures in bedded shale based on phase-field method

准确预测层理页岩水力裂缝扩展路径对于页岩压裂方案优化与压裂效果评价至关重要。基于多孔弹性理论和能量最小化原理建立水力耦合的相场模型,采用交错策略的分离式耦合方法进行求解。通过压裂试验数据对比验证模型的可靠性,同时基于页岩三维水力压裂模拟分析,验证该方法对于模拟不同地应力条件下的水力裂纹扩展问题的适用性。基于该模型,利用插值函数表征页岩层理与基质的力学和渗流参数,研究不同层理角度与地应力差工况下,水力裂缝、天然裂隙以及层理面三者之间的交互作用。研究表明:页岩的层理面改变了水力裂缝预期的扩展路径,该作用效果取决于层理角度。随着地应力差的增大,水力裂缝的扩展路径以及与天然裂隙、层理面交互模式逐渐由地应力差所控制。相场法模拟多场耦合环境下的复杂裂纹扩展与交互等现象相对于其它数值方法具有显著优势。

Accurate prediction of the propagation path of hydraulic fractures in shale plays an important role in optimizing fracturing schemes and evaluating fracturing effects.Based on the theory of poroelasticity and the energy minimization principle,a hydro-mechanical coupling phase-field model is established.The segregated coupling method based on the staggered scheme is adopted to solve it numerically.The reliability of the model is verified by the existing experimental results.The simulation analysis of 3D hydraulic fracturing confirms the feasibility of the proposed method in capturing the propagation path of hydraulic fractures under different in-situ stress configurations.Based on the model,the mechanical and seepage parameters of bedding planes and matrix are characterized by the interpolation function.The interactions among hydraulic fractures,natural fractures and bedding planes are investigated under different bedding angles and in-situ stress configurations.The results show that the bedding planes of shale alter the expected propagation path of hydraulic fractures,which depends on the bedding angle.With the increase of in-situ stress difference,the propagation path of hydraulic fractures and the interaction mode are gradually controlled by the in-situ stress difference.Compared with other numerical methods,the phase-field method has a significant advantage in simulating complex crack propagation and interaction in coupled multiphysics environment.