Abstract: The thermal stress, casing pressure and non-uniform geologic stress loaded on the casing and cement sheath of horizontal shale gas wells due to volumetric fracturing operations can produce significant influence on sealing integrity of cement. A numerical wellbore temperature model for fracturing is presented that has considered the unsteady heat transfer process of formation. The mechanical model of casing, cement and formation is established coupling the thermal stress, casing pressure and non-uniform geologic stress. The sealing integrity and mechanical characteristics of the vertical section of a shale gas well is calculated and analyzed. The result shows that the cement sheath along the maximum horizontal principle stress is easily to break down, it is the key orientation for sealing integrity. The higher the temperature difference in the wellbore, the lower the circumferential stress. The higher the pump pressure at wellhead or the more uneven the horizontal stress, the higher the circumferential stress at the inner surface of inner cement sheath, and the more likely the tensile failure. Lower fracture pressure and wellbore temperature are the effective methods to reduce circumferential stress. The research has a practical reference for cementing operation and fracturing operation.

Key words:  , wellbore temperature, nonuniform geologic stress, multiple string, tensile failure

摘要： 体积压裂施工引起页岩气水平井套管 -水泥环受到温度场、套管内压、非均匀地应力的综合作用，对水泥环的密封完整性具有重要影响。文章考虑了地层非稳态传热效应，建立了体积压裂井筒温度场数值计算模 型，计算了压裂过程中的井筒温度分布；考虑温度场和非均匀地应力的耦合作用，建立了井筒套管 －水泥环 －地层 系统多层组合体的力学模型，对某页岩气水平井的直井段水泥环密封完整性进行了力学计算与分析，结果表明，最 大水平地应力方向的内层水泥环内壁最易出现拉伸破坏，是影响井筒完整性的关键位置；压裂液排量越大或注入 温度越低，水泥环环向应力越低；水平地应力的非均匀程度越高，水泥环内壁环向应力越大，越容易出现拉伸破坏； 合理控制注入温度和压裂排量，是降低环向应力、防止水泥环拉伸破坏的有效方法。文章研究对固井施工与压裂 作业控制具有实际参考意义。

关键词:  井筒温度, 非均匀地应力, 多层管, 水泥环, 拉伸破坏