Strategies for Prevention of Downhole Tool Failure Caused by High Bottomhole Temperature in Geothermal and HPHT Oil and Gas Wells

AbstractHigh bottom hole temperature can lead to decreased downhole tool life in geothermal and high temperature / high pressure (HPHT) oil and gas wells. The temperature increase is exacerbated when circulation stops, e.g., during connection, tripping, well control situations, etc. While continuous circulation technology is an appropriate solution for managing temperature, it is not yet widely adopted in HPHT and geothermal drilling practices. This work investigates factors that impact downhole temperature and recommends strategies to better manage the temperature when continuous circulation is not available.An integrated thermo-hydraulic model was developed to capture the transient behavior of downhole temperature and was applied here to study the transient temperature profile when there is no fluid circulation. The model was validated using the open-source FORGE field dataset, with the mean absolute percentage error (MAPE) between 1-4%. In addition, hundreds of case scenarios were numerically studied to investigate the impact of several key factors on the downhole temperature.The evaluated factors include the pump-off time, type and physical properties of the drilling fluid, wellbore hydraulic diameter, reservoir temperature, geothermal gradient, total wellbore depth and profile, and operational parameters prior to stopping the circulation. The cooling effects of different drilling parameters were compared to a benchmark case of continuous circulation. A correlation map was generated to visualize the impact of those parameters on the downhole temperature distribution when circulation stops. A logarithmic relationship between the pump stop time and the downhole temperature was observed. For the FORGE case scenario, the downhole temperature increases by 27 °C and 48 °C after the pump stops for 30 and 60 minutes, respectively. It was observed that water-based mud with a high viscosity increases fluid convection heat resistance between the formation and wellbore. Also, drilling with a higher flow rate before stopping the pump can cool the near-wellbore formation faster and reduces the downhole temperature even after circulation ceases. Wells with high geothermal gradients, like FORGE wells, have higher temperature build-up during circulation stoppage than wells with low geothermal gradients targeting the same reservoir (formation) in-situ temperature.This study investigates the efficacy of different cooling strategies to avoid downhole temperature build-up when there is no circulation. It thereby facilitates the optimization of geothermal and HPHT well design and construction to prevent downhole tool failures. The developed correlation map can aid drilling engineers understand the impact of different drilling conditions on the downhole temperature.