套管内压周期变化水泥环应力计算与失效分析  

Stress Calculation and Failure Analysis of Cement Sheath Experiencing Periodic Variation of Casing Internal Pressure

作　　者：刘奎 丁士东[1] 周仕明[1] 陶谦[1] 杨广国[1] 刘仍光[1] 高元 Liu Kui;Ding Shidong;Zhou Shiming;Tao Qian;Yang Guangguo;Liu Rengguang;Gao Yuan(State Key Laboratory of Shale Oil and Gas Enrichment Mechanisms and Effective Development,Sinopec Research Institute of Petroleum Engineering)

机构地区：[1]页岩油气富集机理与有效开发国家重点试验室,中国石油化工股份有限公司石油工程技术研究院

出　　处：《石油机械》2021年第5期1-8,共8页China Petroleum Machinery

基　　金：国家科技重大专项“高压低渗油气藏固井完井技术”(2016ZX05021-005);“涪陵页岩气水平井钻完井技术研究”(2016ZX05060-12);中国石化科技部项目“文23储气库井筒完整性评价技术与标准研究”(PE19015)。

摘　　要：套管内压周期变化导致的水泥环密封失效已经严重影响到天然气的安全高效开发,试验结果显示,是否考虑地层岩石的存在将导致研究结果中水泥环破坏方式的差异。鉴于此,建立了不同地层岩石存在情况下水泥环应力状态力学分析模型并计算了水泥环的应力状态。研究结果表明:未考虑地层岩石约束时水泥环发生的拉伸破坏与试验结果相同;考虑地层岩石约束的水泥环,由于套管和水泥环外壁地层岩石的约束,水泥环径向裂纹的发生和发展受到限制,即使套管内压增加使水泥环周向应力大于其抗拉强度,水泥环上仍然不会产生径向裂纹;周期载荷作用下水泥环的残余应变将造成套管-水泥环界面径向压应力降低甚至变为径向拉应力,产生界面微环隙,这是最终导致水泥环密封失效的主要因素。研究成果可为油田现场固井优化设计提供参考。The seal failure of cement sheath caused by periodic variation of casing internal pressure has seriously affected the safe and efficient development of natural gas.The current cement failure test results show that whether the existence of formation rock is considered,it will lead to the difference of cement sheath failure mode in the research results.Therefore,in this paper,the mechanical analysis model of cement sheath stress state in the presence of different formation rocks was built,and the stress state of cement sheath was calculated.The research results show that the tensile failure of cement sheath is the same as the experimental results when the formation rock constraint is not taken into account;when the formation rock constraint is considered,due to the constraints of casing and formation rock on the outer wall of cement sheath,the occurrence and development of radial cracks in cement sheath are restricted,even if the increase of casing internal pressure makes the circumferential stress of cement sheath greater than its tensile strength,radial cracks will still not occur on the cement sheath;under the action of cyclic loading,the residual strain of the cement sheath will cause the radial compressive stress of casing-cement sheath interface to decrease or even change into radial tensile stress,resulting in interfacial micro-annulus,which is the main factor leading to the seal failure of the cement sheath.The research results can provide reference for field cementing optimization design.

关 键 词：水泥环 密封失效 拉伸破坏 残余应变 微环隙 

分 类 号：TE925[石油与天然气工程—石油机械设备]