Analysis of surface drilling fluid cooling for wellbore temperature regulation in extra-deep drilling

Abstract:

To address the critical challenges in extra-deep drilling beyond 10000 meters， such as downhole tool failures and drilling fluid performance degradation caused by extreme high temperatures， this study investigates the efficacy of surface cooling of drilling fluid. A numerical model of wellbore-formation coupled heat transfer was established and validated against measured data from Well Yaha 501. Using the bottom-hole circulating temperature， maximum drilling fluid temperature， and return drilling fluid temperature as key evaluation metrics， simulation analysis was conducted to examine the temperature control performance of surface cooling at designed depths of 8000 m， 11000 m， and 13000 m. The results demonstrate that implementing surface cooling reduced the bottom-hole circulating temperature and maximum drilling fluid temperature by 24.3 ℃ & 24.4 ℃， 17.4 ℃ & 17.9 ℃， and 12.0 ℃ & 12.5 ℃， respectively. Without cooling， the return drilling fluid temperature after four circulation cycles reached 92.3 ℃， 96.2 ℃， and 94.3 ℃. In contrast， with surface cooling， it stabilized at approximately 60 ℃. This study provides a theoretical basis and quantitative guidance for wellbore temperature control and safe operations in extra-deep drilling.