复杂气井套管力学分析与可靠度评价

为建立考虑地层和套管参数随机性的套管可靠度评价理论方法，以便得到复杂井况下套管传统设计安全系数与可靠指标之间的关系，提出了非均匀地应力和内压联合作用下，沿套管最大外挤力方向管壁任意位置发生屈服失效时外壁等效均匀外挤力的计算方法；建立了套管抗挤和抗内压三轴强度计算公式以及有效内压计算方法；根据套管载荷和强度影响因素统计参数以及评价过程中参数测试标准值，利用蒙特卡洛法（MC）建立了完整的套管可靠度计算和评价方法；通过实例对传统安全系数与可靠指标的对应关系进行了研究。研究结果表明:指定条件下，套管安全系数与可靠指标之间存在对应关系；利用建立的方法编制计算程序可以为传统设计法中安全系数代表的安全程度进行量化；可靠度评价方法能够为安全系数的选取提供指导。

Mechanical analysis and reliability evaluation on casing of complex gas well

In order to establish a theoretical method for the reliability evaluation of casing with considering the randomness of formation and casing parameters, so as to obtain the relationship between the safety factor in traditional design and reliability index of the casing under the complex well conditions, a method for calculating the equivalent uniform external pressure of the outer wall of casing when the yield failure appeared at any position along the direction of the maximum external pressure of casing under the combined effect of non uniform in situ stress and inner pressure was proposed. The calculation formulas of triaxial strength for anti collapse and resisting inner pressure of the casing were established, as well as the calculation method of effective internal pressure. According to the statistical parameters of impact factors of the casing load and strength as well as the standard values of parameters in the evaluation process, a complete reliability calculation and evaluation method of the casing was established by using the Monte Carlo (MC) method, and the corresponding relationship between the traditional safety factor and reliability index was studied by an example. The results showed that there was a correspondence relationship between the safety factor and reliability index of the casing under the specified conditions. Preparing the calculation program by using the established method could quantify the safety level represented by the safety factor in the traditional design method. The reliability evaluation method can provide the guidance for the selection of safety factor.