非均匀地应力下套管应力的敏感性分析

Sensitivity Analyses of Casing Stress Under Non-uniform In-situ Stress

套损是影响地下储气库井筒完整性的关键问题,制约着储气库长期的安全生产。为此,基于弹性力学理论,运用有限元分析方法,建立了理想固井状态下的套管-水泥环-地层组合分析模型,对受非均匀地应力时组合体各层Mises应力的分布规律进行了研究,讨论了套管应力对水泥环与地层的弹性参数变化的敏感程度。结果表明:套管内壁的应力明显高于水泥环和地层内壁的应力且沿井周呈非均匀分布;地层弹性模量对套管内壁应力的影响最为显著,套管应力随地层弹性模量的增加急剧减小;其次为水泥石弹性模量,当其与地层弹性模量相同时,套管应力达到最大。该研究成果可为优化套管完井设计和预防套管损坏提供理论参考。

Casing failure is a key problem affecting the wellbore integrity of underground gas storage and restricts the long-term safe production of gas storage. Therefore, based on the elastic mechanics theory, a combination analysis model of casing-cement sheath-formation under ideal cementing state was established using finite element analysis.The Mises stress in each layer of the combination was studied under non-uniform in-situ stress, and the sensitivity of casing stress to elastic parameters of cement sheath and formation was discussed. The results showed that the stress in the inner wall of casing was obviously higher than that in the cement sheath and the inner wall of formation, and the stress was non-uniform along the well circumference. The formation elastic modulus had the most significant effect on casing wall stress, and casing stress decreased sharply with the increase of it. Secondly, the casing stress reached the maximum when the elastic modulus of cement was the same as that of formation. The research results can provide a certain theoretical reference for optimizing casing completion design and preventing casing damage.