基于页岩各向异性的裂缝起裂数值模拟分析

Numerical analysis of fracturing initiation based on anisotropic shale

 李玉梅¹ 柳贡慧 2 李军¹ 于丽维³ 杨宏伟^１ 连威^１

中国石油大学（北京）石油工程学院，北京102249 北京工业大学，北京100124 中国石油新疆油田公司工程技术研究院，新疆 克拉玛依834000）

College of Petroleum Engineering, China University of Petroleum, Beijing 102249, China Beijing University of Technology, Beijing 100124, China Engineering Technology Research Institute, Xinjiang Oilfield Company, Karamay 834000, China)

 页岩层理在水平方向上有序地定向排列结构导致了页岩较强的弹性各向异性。基于岩石横观各向同性本构关系以及渗流与变形耦合数值方法，建立了水平井裂缝起裂的三维有限元数值模型。考虑页岩弹性力学参数各向异性差异，进行了射孔参数和非均匀地应力对水平井裂缝起裂压力和起裂位置的敏感性研究分析。研究结果表明：裂缝起裂点对射孔方位角有较强的敏感性，随射孔方位角的增大易出现复杂的裂缝起裂形态；裂缝起裂压力随射孔方位角的增大而增大，随射孔密度的增大而减小；弹性模量各向异性对起裂压力有较大的影响，弹性模量各向异性比值越大，起裂压力越小；无论是均质地层还是各向异性地层，水平地应力比值对起裂压力的影响较大，初始水平地应力比值对起裂压力的影响较小。计算结果可为页岩储层的裂缝起裂压力预测以及裂缝扩展机理深入研究提供参考。

An orderly structure of shale beddings aligned in the horizontal direction causes the strong elastic anisotropy of shale. Based on rock transverse isotropic constitutive relation and the seepage and deformation coupling numerical method, a three-dimensional finite element numerical model for horizontal well with perforating completion was established. Considering the elastic mechanics anisotropy differences of shale, the sensitivity analysis of perforating parameters on the fracture initiation pressure and location of horizontal well was proposed. The finite analysis results show that fracture initiation points are very sensitive to perforation azimuth, and complex fracture initiation morphology is prone to forming with the increase of perforation azimuth; the increasing of perforation angle and decreasing of perforation density lead to a higher fracture initiation pressure; the elastic modulus anisotropy degree has great influence on fracture initiation pressure, the greater the elastic modulus anisotropic ratio, the smaller fracture initiation pressure; whether the formation is homogeneous or anisotropic, the influence of the horizontal in-situ stress ratio on the fracture initiation pressure is greater, while the influence of the initial horizontal in-situ stress ratio on the fracture initiation pressure is smaller. The analysis results provide a valuable and effective guidance for the prediction of fracture initiation pressure and fracture propagation mechanism under special stratum conditions.

10.6056/dkyqt201603024