Strength Time Varying Analysis of Casing with CO2 Corrosion Defects

Abstract

The time-varying of the casing string strength is analyzed in view of the CO2 corrosion effect. The pressure-temperature coupling calculation is given with the dual iterative computation method. In the direction of well depth, the distribution of pressure and temperature are obtained, and then the computation prediction model of CO2 corrosion rate for casing string is built based on the Norsok model. According to the well testing theory in the fixed value production stage, the relationship between the wellhead pressure and the time is obtained through the well logging data regression. By introducing the pressure-temperature time-varying law into the CO2 corrosion rate prediction model, the remaining strength time-varying analysis model of the casing string in CO2 corrosion environment is established. Calculation results indicate that the casing strength decreases with time because of the wall thickness reduction due to CO2 corrosion, the remaining strength of casing string drop quickly in the early stable stage, and getting slow down as the time increases. The reducing extent of casing limit collapse destroyed strength is bigger than the limit internal strength and the body tensile strength by uniform corrosion affection.