页岩气储层定向射孔压裂裂缝转向影响因素分析

Factors affecting reorientation of hydraulically-induced fracture during fracturing by oriented perforations in shale reservoirs

针对页岩气藏水力压裂过程中裂缝起裂、扩展和转向规律的认识尚不够清楚的问题,基于扩展有限元法(extended finite element method,XFEM)建立了用于页岩气储层直井定向射孔水力压裂裂缝同步扩展和转向状况模拟的流-固耦合2D模型,分析了射孔方位角、压裂液注入速率、地层水平应力差异等因素对水力裂缝的起裂压力和转向半径的影响。研究结果表明:1)随着射孔方位角的增大,裂缝的起裂压力和转向半径均越来越大,不利于具有较好压裂改造效果的平直裂缝的形成;2)在较大的压裂液注入速率下,裂缝起裂压力较大,转向半径也较大,储层的压裂改造效果更好;3)对于地应力差异较大的储层,裂缝起裂压力会更小,裂缝转向会表现得更为显著。研究结果全面揭示了不同因素对裂缝起裂和转向的影响,可以为页岩气水力压裂设计提供参考和理论支持。

To clearly understand the initiation and reorientation of hydraulically-induced fractures during hydraulic fracturing in shale gas reservoirs,a fluid-solid coupling 2D model for simulating propagation and reorientation of hydraulically-induced fractures is established with the extended finite element method(XFEM).And the effects of factors such as perforation azimuth angle,injection rate of fracturing fluid and difference between horizontal stresses on fracture initiation and reorientation during hydraulic fracturing in shale gas reservoirs are analyzed.The results show that both the initiation pressure and reorientation radius of hydraulically-induced fracture will increase with the increase of the perforation azimuth angle,which is not conducive to the formation of straight fractures with better fracturing reconstruction.In addition,when a large injection rate of the fracturing fluid is designed during fracturing operation,the initiation pressure of hydraulically-induced fracture will be higher and its reorientation radius will be larger,which leads to better fracturing reconstruction effect.Finally,for reservoirs with large difference large difference between two horizontal principal stresses,initiation pressure will be lower and fracture turning will be more significant.The above investigation results fully reveal the influence of different factors on fracture initiation and fracture reorientation during fracturing operation,which can provide theoretical support for practical fracturing design in shale gas reservoirs.