深井超深井套管风险评估方法

套管强度设计标准未考虑制造缺陷,且深井超深井套管安全系数难以确定,为弥补这些不足,提出一种基于目标可靠指标的含缺陷套管风险评估方法。首先,建立考虑套管制造缺陷的套管强度和外载计算方法,并基于强度和载荷影响因素的随机性,利用蒙特卡罗(MC)法获取强度和载荷的分布类型和参数;其次,确定目标可靠指标,对拉克维茨-菲斯勒(R-F)法逆向迭代求解,并结合分项系数法,确定套管强度和载荷的分项系数;最后,根据分项系数和套管外载标准值确定套管所需的最低强度值,选择套管或判断已选套管是否满足安全可靠性的要求,并作实例分析。结果表明:该风险评估方法能够满足深井超深井套管设计和选型的工程实际需要;能够弥补传统设计法中安全系数选取困难的现状。

Risk assessment method of casing for deep and ultra-deep wells

In view of the facts that the manufacturing defects were not considered in current casing strength design standards,and that the safety factors of casing was hard to identify,a risk assessment method of the casing with defects based on the target reliability index was proposed. Firstly,calculation methods of the strength and external load of casing considering manufacturing defects were established,and the distribution types and parameters of strength and load were calculated by Monte Carlo( MC) method on the basis of the randomness of factors influenching strength and load. Secondly,by determining the target reliability index and solving the Rackwitz-Fiessler( R-F) calculus points using inverse iteration,the partial coefficients of casing strength and load were determined. Finally,the minimum strength value required for casing was determined according to the partial coefficients and casing load standard value,and the casing was selected or judged based on the safety and reliability requirements. An oilfield was taken as an example to verify the proposed method. The results show that the risk assessment method established in this paper can meet the practical project needs of casing design and selection for deep and ultra-deep wells,and can help to solve the difficulty of selecting safety factors in the traditional design method.