多随机因素作用下储气库套管运行期安全性分析

Safety analysis of casing of gas storage influenced by stochastic factors during operation period

套管是地下储气库运行过程中的薄弱环节,各随机因素的变化会对套管系统安全性产生较大的影响。以三维套管-水泥环-围岩系统为研究对象,考虑几何尺寸、荷载、材料特性等多因素的随机特性,基于蒙特卡罗法对储气库运行期套管系统的失效概率及敏感性因素进行分析,通过与地质模型试验结果进行对比,验证了数值模拟结果的可靠性。结果表明,各随机因素对套管系统可靠性的影响程度不同,其中套管厚度、套管内径、工作内压、水泥环厚度为高敏感性因素,且各因素的影响效果不同,在工程中可采取不同措施提高系统可靠性;采气阶段,根据储气库腔体应力状态和体积变形规律确定的最大采气降压速率不会影响套管系统的安全性。

Casing is a weak part of underground gas storage during its operation period, which will be influenced by kinds of stochastic factors. In this paper, failure modes and failure criterions of casing and cement sheath are discussed firstly; then a three dimensional calculation model including casing, cement sheath and wall rock is established based on Jintan underground gas storage in Jiangshu province. Stochastic characters of geometrical size, load and material parameters of the casing system are analyzed, which are applied to the safety analysis. Then, failure probability and sensitive factors are calculated based on Monte Carlo method. At last, the simulation result is proved by a three dimensional geological model experiment. The research results indicate that the influences of the randomness responding to factors on casing reliability are different. Thickness of casing, inner diameter of casing, operation pressure and thickness of cement sheath are sensitive factors of casing-cement and wall rock system. Moreover, different factors have different effects on reliability. The reliability of casing decreases as storage pressure decreasing. And the reliability of cement sheath decreases as storage pressure increasing. More attention must be paid because failure probabilities of casing are high when the gas pressures of storage are extremely high or low. The gas extraction rates determined by the volume convergence law of the caverns will not influence the safety of casing-cement and wall rock system.