A method to assess the reliability of casings in marine gas reservoirs based on Bayesian theory optimization

With the exploitation of marine gas fields including Puguang, Yuanba and Longwangmiao in Anyue, casings have been thinned, deformed, ruptured or even broken by various factors after a long time of service. Therefore, it is important to assess the reliability of casings used in marine gas reservoirs. Based on Bayesian theory and the current status, the prior information is used to screen and simplify influencing factors, to optimize models. According to the standard of collapsing strength and the numerical simulation, optimized models to assess the reliability of casings in marine gas reservoirs are established, applied and compared. The results provided by these optimized models showed a downward trend, but the ranges and gradients of variation are quite different. The results calculated for uniform loads and non-uniform loads are close to each other, as indicated by the sensitivity analysis. To make use of the advantages in two assessment methods, first, a preliminary screening to the casings with hidden danger is achieved by the method based on the collapsing strength. Then, the method based on the numerical simulation is used to assess the remaining risky casings.