Full-Scale Experimental and Numerical Insights into Bullheading Efficiency for Geothermal Steam Kicks: Bridging Countercurrent Flow Dynamics and Transient Heat Transfer

Abstract Geothermal well control presents unique challenges due to elevated temperatures and complex multiphase flow behavior during steam kicks and wellbore flashing events. Bullheading has been recognized as an effective method for managing these scenarios due to its ability to forcibly pump fluid down the wellbore to both suppress steam kicks and reduce wellbore temperature; however, there remains a knowledge gap regarding countercurrent steam-liquid flow dynamics and the transient heat transfer phenomena specific to high-temperature geothermal conditions. This study addresses this critical gap through comprehensive full-scale experiments, supported by transient multiphase modeling, to facilitate the development of optimized well control strategies for geothermal well construction. The research methodology combined full-scale physical experiments with advanced numerical modeling. Experiments were conducted at Louisiana State University's PERTT facility, where nitrogen gas kicks were injected into a 5,800-ft wellbore filled with a representative water-based mud. The bullheading process was comprehensively monitored using downhole pressure gauges and Distributed Temperature Sensing (DTS). This experimental data provided a unique dataset for validating the thermal-hydraulic predictions of the RELAP5-3D multiphase flow simulator. The validated model was then used to investigate true geothermal scenarios, simulating wellbore flashing and the subsequent bullheading of a steam kick under high-temperature conditions. Experimental results detailed the dynamics of non-condensable gas compression and displacement and confirmed the model's accuracy in predicting pressure and temperature profiles, with validation yielding correlation coefficients above 0.95. The subsequent numerical simulations of steam kicks revealed that the primary challenge is not managing buoyancy but mitigating the water hammer pressure transients caused by rapid steam condensation. Parametric studies demonstrated that higher injection rates accelerate kick suppression but significantly increase the magnitude of water hammer events, whereas injection fluid temperature has a secondary effect. This work provides critical insights into the fundamentally different physics governing conventional gas versus geothermal steam kick bullheading. By anchoring advanced simulations with full-scale experimental data, this study offers validated, practical strategies for optimizing bullheading operations, enhancing safety, and ensuring well integrity during geothermal drilling.