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Drilling and other well construction operations in high-temperature geothermal wells face a fundamental challenge: preventing downhole tool failure caused by exceeding temperature limits. Tripping into such wells needs to be staged to lower the possibility of thermal tool damage. This study investigates the bottomhole assembly (BHA) temperature evolution, cooling effectiveness, and operational design of staged trip-in practices in geothermal and other high-temperature wells. A thermo-hydraulic modeling framework is developed, combining a full-well finite volume model (FVM) with a lumped BHA-wellbore model, to capture transient well thermodynamics during drilling and staged trip-in operations. Model validation using Utah Forge Well 16B(78)-32 data shows that the root mean square error (RMSE) of bit/BHA temperature prediction ranges from 4°F (2.2°C) to 8°F (4.4°C). Sensitivity analyses demonstrate that the maximum stage length remains under 4-5 stands when tripping into wellbores with near-field formation temperatures in the range of 250°F (121°C) to 320°F (160°C) unless significant well geometry or mud property changes occur. The only strategy that consistently extends downhole sensor survivability beyond 8-10 stands is BHA external thermal insulation. Simulation results demonstrate that adding a field-proven 0.15 in (3.8 mm) coating with thermal conductivity of 9 BTU.in/hr/ft 2 /°F (1.30 W/m/K) can reduce BHA temperatures by up to 30°F (17°C), compared to unprotected configurations under these downhole conditions. The modeling and analysis can also help identify scenarios where staged circulation is insufficient and continuous circulation (i.e., circulation while making connections) is required to maintain safe tripping BHA temperatures. These findings provide practical and insightful guidance for the design of effective cooling strategies during geothermal and high-temperature oil and gas well drilling and tripping operations, ensuring safer and more efficient operations in extreme downhole thermal environments with a lowered risk of BHA component failure.
Zhang et al. (Fri,) studied this question.