Study on Multi-string Wellhead Growth Prediction in High Temperature Wells and Analysis of On-Site Example

In high temperature wells such as thermal recovery wells or ultra-deep wells, it is prone to experiencing wellhead growth during the production process. Most current research focuses on the free extension of single casing in the uncemented section of the wellbore, but the most of their results significantly diverges from actual observations. Therefore, it is necessary to establish a method for predicting wellhead growth height considering the length of casing-cement sheath debonding and multi-string effect. In this study, the thermal debonding mechanism of casing-cement sheath was theoretically analyzed, and a calculation model for the debonding length of casing-cement sheath was obtained. Then, based on the frictional resistance of the cement sheath and the coupling effect of multiple layers of casing, a method for predicting wellhead growth height was further established. Finally, the sensitivity analysis of influencing factors of wellhead growth was carried out and a case study was conducted on an offshore well in the South China Sea. The results showed that: (1) The predicted wellhead growth height is in good agreement with the measured results, with a maximum relative error of only −5.63%, validating the effectiveness and accuracy of the wellhead growth height prediction model for on-site application. (2) The wellhead growth height is positively correlated with production speed, production time and thermal conductivity of tubing, and negatively correlated with the casing-cement bonding load. (3) The influence of production speed should be considered when installing wellheads, and cementing quality should be improved for preventing wellhead growth in actual field operations. This study can provide reference and significant implications for preventing and reducing wellhead growth issues in high temperature wells.