A Simplified Hydrodynamic Model and Automatic Kick Control for Subsea Pump-Lift Dual-Gradient Drilling

Although the world is rich in deepwater oil and gas resources, deepwater drilling faces the challenge of a narrow safety density window. Dual-gradient drilling is an effective approach to address this narrow safety density window, and subsea pump-lift dual-gradient drilling is currently one of the most widely used methods. To improve handling capacity and effectiveness under well kick conditions, we established a simplified hydrodynamic model for subsea pump-lift dual-gradient drilling that accounts for the subsea pump’s head-flow performance curve. Based on this hydrodynamic model, we proposed automatic control methods based on throttling regulation and variable-speed regulation and conducted simulation analyses. The results indicate that both control methods can safely, efficiently, and automatically handle well kicks; throttle control has shorter response times and higher precision, while variable-speed control regulates bottom hole pressure by adjusting the subsea pump’s rotational speed and offers better energy-saving performance. These findings provide new insights into handling well kicks in subsea pump-lift dual-gradient drilling.