基于扩展有限元的单径向井压裂裂缝扩展规律

径向井压裂技术已应用于多个油田并取得良好效果，而径向井对裂缝扩展的影响规律仍待研究。基于地层流-固耦合方程，建立扩展有限元（XFEM）模型，利用最大主应力准则、最大能量释放率准则判断裂缝的起裂与扩展，量化分析了不同参数对裂缝形态的影响规律，并对影响因素进行了灰色关联分析，最后通过大型真三维物模实验在一定程度上验证了数模结果的正确性。结果表明，压裂液通过径向井壁向地层渗滤形成了沿径向井分布的诱导应力场，在一定范围内，径向井产生的诱导应力可实现主裂缝沿径向井方向定向扩展，有效引导距离可达40m；水平地应力差、储层厚度的增大均会大幅降低径向井引导裂缝定向扩展的能力；径向井方位角的增大会显著增大起裂压力。研究成果对现场应用具有重要的指导意义。

Research on the Propagation Law of Single Radial Well Fracturing Based on XFEM

The technology of radial well fracturing has been applied in various oil fields and achieved effective output. However, the influence that the hole of radial well on fractures should be studied further. In this paper, based on fluid-solid coupling equation, the factors that different parameters of radial well on crustal stress were solved nonlinearly by using ABAQUS. Initial fracturing position and propagation morphology were identified according to maximum tension-stress criterion and maximum energy release rate fracture criterion. In the end, results obtained from 3D physical experiment in the laboratory were used to verify the accuracy of simulation to a certain degree. The conclusions stated that original crustal stress field distribution was changed during the radial well fracturing and the induced stress field is established along the radial well at the same time. The propagation of major fracture is orientated by the induced stress in a certain area. The distance of orientated fracture is able to 40 meters. The increase of horizontal stress difference and reservoir thickness is unfavorable to effect of orientated propagation of fracture. The results are significant to the practice and production.