中文摘要：

页岩气等致密油藏开发过程中常采用分簇射孔和复合桥塞分段大型水力加砂压裂的方式来改造储层,在作业过程中出现了大量的油层套管失效现象,导致正常的完井增产作业无法进行,严重影响了增产效果,降低了完井质量。为此,运用ABAQUS有限元分析软件建立地层-水泥环-套管的三维有限元模型,模拟计算压裂后套管Mises应力及变形分布。通过对有限元结果分析和对比压裂后MIT多臂测井曲线,认为套管失效原因为压裂后局部地层岩石强度非均匀降低,套管受挤压变形,致使套管截面椭圆度和弯曲曲率过大,导致井下工具下入遇阻遇卡。最后提出压裂过程中应该根据地层岩性和地应力参数选择合理的完井方式、压裂层段或分段方式和长度,加强随压裂监测技术,实时优化压裂分段、分簇工艺和施工压力参数,为页岩气压裂引起套管失效的防治提供理论依据。

英文摘要：

The technique of cluster perforation and large-scale staged hydraulic sand fracturing with composite bridge plugs is deployed to stimulate tight reservoirs for development of shale gas. During operations,failure of production casings occurred frequently,which have impeded completion operations and significantly reduced stimulation performances. Accordingly,a 3D finite-element model for the formation-cement sheath-casing is established using ABAQUS. According to results of finite element analysis and through comparison of MIT logs after fracturing,it is determined that failures of casings are induced by uneven reduction in strengths of formation rocks after fracturing. Under such circumstances,casings may be squeezed and deformed,and during the course generate excessive ellipticity and curvatures of casings and eventually stuck downhole assemblies. This paper proposes that proper completion techniques should be deployed with proper fracturing intervals or suitable lengths of such intervals and specific division methods determined in accordance with formation properties and crustal stresses during fracturing. In addition,monitoring-while-fracturing should be adopted,and fracturing stage and clustering technologies and operation pressures should be optimized in real time.