定向射孔水力压裂复杂裂缝形态

在岩石力学试验测试和现场资料解释的基础上,建立了三维弹塑性有限元模型,通过大量计算研究了定向射孔水力裂缝形态的影响因素.研究结果表明,定向射孔水力裂缝起裂主要受相邻射孔之间应力干扰的影响,而影响定向射孔水力裂缝形态的主要因素为定向射孔方向与最大地应力方位的夹角和水平应力差.水力裂缝不一定沿着定向射孔的方位起裂;定向射孔形成的水力初始裂缝一般为锯齿状;在水平应力差和射孔夹角较大的情况下,容易形成由定向射孔和最大地应力方位起始的双裂缝.提高地应力测试和定向射孔的精度可以有效避免复杂形态水力裂缝的产生.图7参13

Complex fracture shapes in hydraulic fracturing with orientated perforations

Based on rock mechanical tests and practical data interpretation, a three dimensional finite element model is established to study factors influencing fracture shape in orientated hydraulic fracturing. The stress interference around neighboring perforations causes fracture initiation, and the main factors influencing fracture shapes are horizontal principal stress difference and the angle between the perforation orientation and the maximum horizontal stress. The computations also reveal that hydraulic fractures will not always initiate along perforation orientation, and usually the initial hydraulic fracture is in a zigzag shape. When the horizontal stress difference and the perforation angle are great, dual fractures will happen along perforation and the maximum stress directions. So improving the accuracy of stress measurement and orientated perforation can avoid the generation of complex-shape hydraulic fractures.