用可靠性理论分析传统套管设计中存在的问题

Analysis of defects in traditional method of casing design by reliability theory

鉴于套管几何尺寸和力学性能的随机性,采用蒙特卡罗随机模拟方法模拟出套管强度的随机分布规律,分析了套管几何尺寸和力学性能的随机性对套管强度随机性的影响,计算得出了套管强度的分布参数及API值的可靠度。运用可靠性理论建立了套管的可靠性计算模型,分析了套管可靠性的影响因素,得到了载荷随机性对套管可靠性的影响规律以及安全系数与套管可靠度之间的关系。研究结果表明,套管几何尺寸和力学性能的随机性越大,则套管强度的随机性越大,传统套管强度计算公式中未合理考虑该随机性;套管强度和载荷的较大随机性明显地降低套管的可靠性,而传统套管设计方法无法有效评价该随机性对套管安全可靠性的影响。

On account of the randomness of casing＇s geometric dimension and mechanical properties, the regularities of distribution of casing strength were obtained by Monte-Carlo method. The influence of the randomness of casings geometric dimension and mechanical properties on the randomness of casing strength was achieved. Both the distribution parameters of casing strength and the reliability of API casing strength were worked out. The reliability model of casing was established by reliability theory. The influencing factors of casing reliability were analyzed. The influence of the randomness of loads on the reliability of casing, and the relationship between the reliability and safety coefficient of casing were obtained. The resuits indicate that the more random casing＇s geometric dimension and mechanical properties are, the more random the casing strength is. The randomness was not be considered in the traditional formulas of casing strength rationally. The extraordinary randomness of casing strength and load can obviously reduce the reliability of casing. The influence of the randomness on the reliability of casing can＇t be evaluated effectively in the traditional method of casing design.