Downhole heat management for drilling shallow and ultra-deep high enthalpy geothermal wells

Heat management while drilling high-enthalpy geothermal wells is crucial for successful drilling and commercial energy extraction from hot reservoirs (150+ degrees C). Accurate modeling of heat transfer between drilling fluids and rock is vital to predict the transient bottom hole circulating temperature (BHCT). This allows downhole tools and drill bits to operate within their temperature limits, thereby preventing premature failure while drilling from high-temperature exposure. In this study into the most effective ways to pro-actively manage downhole temperatures, a validated coupled thermal/hydraulic model is used to simulate the transient behavior of BHCT and the mud temperature profile inside the drill string and the annulus of geothermal wells. The developed model investigates the effectiveness of different heat management techniques for relatively shallow (< 3 km, 10,000 ft TVD) as well as deep (> 6.1 km, 20,000 ft TVD) high enthalpy geothermal wells. Simulation results show that higher drilling flow rates, use of mud coolers/chillers, use of certain fluid types and viscosities, as well as increased hole size can all be used as strategies to reduce the BHCT of shallow geothermal wells effectively. However, the situation changes for deep geothermal wells and/or wells with long geothermal reservoir exposure, with reduced effectiveness of e.g., mud cooling and other generally accepted cooling measures. For such wells, however, the use of an insulated drill pipe (IDP) in combination with drilling flow rate can be used effectively for heat management. As part of the results, correlation maps are presented to provide drilling engineers with a user-friendly tool to quickly gain an understanding of the impact of various downhole cooling strategies for drilling geothermal wells, which in turn can be used to technically and economically justify their selection in the well design and drilling programs.