Evaluation of Tubing Service Life Based on Corrosion Prediction and Strength Calculation

In high-temperature and high-pressured environments containing CO₂ and H₂S, the failure risk of downhole string is extremely high, which seriously threatens the safety of production. Therefore, it is of great significance to evaluate the service life of tubular column. In this paper, taking offshore gas wells as an example, the Mises stress distribution and temperature distribution were obtained through the shaft-formation finite element model. Then, an appropriate CO₂/H₂S corrosion prediction model was used to calculate the corrosion rate of tubing. Finally, taking the safety factor of tubing as the evaluation criteria of safety performance, the evaluation of tubing service life is completed. The results showed that the Mises stress and temperature at all levels of wellbore increased with the increase of the running depth of tubular column. At the end of tubing, the maximum temperature and Mises stress are 207oC and 447 MPa, respectively. In addition, the corrosion rate of the wellhead tubing is the highest, reaching 0.21 mm/a, according to the operation results of the corrosion model. Based on the above results, the safe service life of the tubing without any anti-corrosion measures is only 24 a. However, when corrosion inhibitors are injected, tubing can be used safely for more than 50 a when the corrosion inhibition efficiency is up to 90%.