深井套管安全可靠性评价方法

Evaluation Method of Casing Safety and Reliability in Deep Wells

考虑到深井套管载荷的不确定性和套管几何尺寸、性能参数等随机性,采用随机理论分析,给出了套管外载与强度的概率分布计算方法,采用Monte-Carlo方法模拟了非均匀载荷作用下套管强度的随机分布规律。应用"强度应力"干涉理论,建立了套管安全可靠度计算方法,对不同类型套管在不同外载条件下危险截面处的可靠度进行了分析,得到了区域套管可靠度与安全系数的关系。结果表明,当套管抗外挤、抗内压可靠度为0.50-1.00时,套管的安全系数为1.00-1.25,在载荷变化条件相同时,安全系数的变化幅度小于可靠度的变化幅度,当安全系数大于1.25时,套管可靠度为1.00。套管安全可靠度分析可为套管传统安全系数的选取和外载不确定的情况下套管柱的设计与评价提供依据。

In order to evaluate the safety and reliability of casing strings in deep wells with uncertain formation data,considering the uncertainty of casing loads and randomness of casing size and performance parameters, a probability distribution calculation method for casing load and strength was provided by ran- dom theory analysis. With the Monte-Carlo method, the probability distribution of casing strength was sim- ulated under non-uniform loading conditions. By using load-strength interference theory, the calculation method of casing reliability was established, which can analyze reliability of different types of casing strings when they are subiected to different loadings in dangerous sections, and a co-relationship between casing re- liability and safety factor was established. Results show that when casing reliability of burst and collapse strengths are in the range of 0. 50-1.00, the related safety factors fall between 1.00 and 1.25. If external loading changes in the same magnitude, the variation of safety factor is less than that of reliability. When the safety factor is greater than 1.25, the casing reliability is 1.0. Safe reliability analysis can provide references for con ventional casing safety factor selection and reliability evaluation under uncertain loading conditions.