Automation of Simultaneous Temperature and Pressure Control in a Geothermal Test Well

Abstract Geothermal drilling operations are highly sensitive to coupled well temperature and pressure dynamics that influence well integrity, fluid properties, downhole tool reliability, and overall drilling efficiency. This paper presents a control-oriented well thermodynamics model and a temperature-pressure controller developed for an 11,500-ft geothermal test well. The model captures dominant heat-transfer between the mud in the drillstring, annulus and surrounding formation through a lumped-parameter formulation. Validation against high-fidelity thermal-hydraulics simulators confirms that the reduced-order model can accurately predict the transient and equilibrium well temperature profiles within minutes. Based on this model, proportional-integral-derivative (PID) controllers were designed and tuned for both inlet mud temperature and mud flow rate across a wide operating range (70°F to 150°F and 30 gpm to 400 gpm). Simulation results show that the integrated managed-temperature-managed-pressure drilling (MTD-MPD) framework can stabilize bottomhole circulating temperature (BHCT) within 1°F of the target in less than 30 minutes while maintaining bottomhole pressure (BHP) fluctuations within 20 psi. The combined MTD-MPD system can compensate for transient thermal-hydraulic coupling effects, ensuring safe BHCT regulation and stable BHP control. The proposed methodology effectively addresses key challenges in geothermal and other high-temperature drilling, providing a robust, efficient, and scalable foundation for real-time downhole temperature-pressure management.