Evaluation Method of Casing Safety and Reliability in Deep Wells

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 random theory analysis.With the Monte-Carlo method,the probability distribution of casing strength was simulated 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 subjected to different loadings in dangerous sections,and a co-relationship between casing reliability 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 conventional casing safety factor selection and reliability evaluation under uncertain loading conditions.