Research On Residual Life Prediction Technology Of Casing With Corrosion Defects

During oil and gas extraction,associated gas such as CO₂and H₂S can induce casing corrosion,resulting in localized casing thinning,strength reduction,and even casing destruction,oil and gas well shutdown and environmental pollution.In this paper,the remaining life prediction method of casing with corrosion defects is studied based on finite element and BP neural network methods.The main research contents are as follows:（1）The finite element model with local corrosion defects is established,and the influence of casing,cement ring,formation parameters and corrosion defect morphology on the mechanical properties of casing is analyzed.The finite element model optimization method is proposed to make the numerical simulation results more in line with the actual situation.（2）The reliability analysis of casing is carried out by using the reliability analysis module of finite element software（Monte-Carlo method）.Through 3000 times of simulation analysis,the calculation results show that the maximum equivalent stress and reliability state value of casing are subject to normal distribution,and the probability density curve and cumulative probability density curve are fitted.According to the cumulative probability equation of the maximum equivalent stress and reliability state value of casing,the confidence interval and sample reliability of the maximum equivalent stress of casing under different confidence levels are obtained.Through sensitivity analysis,the relative influence of casing,formation,cement sheath and load on casing reliability is obtained,which can provide reference for casing safety evaluation.（3）Based on the reliability analysis results,the database is established,and the residual life prediction model of casing is established by using BP neural network method.The residual life prediction chart of casing risk influencing factors is drawn,which provides a reference for the formulation of safety production plan in oil and gas fields.