Research on Bottomhole Pressure Control Method Based on Backpressure Regulation in Deepwater Dual-Layer Pipe Dual-Gradient Drilling

With the growing demand for offshore energy, deepwater drilling has become a vital technology in petroleum engineering. However, conventional drilling systems often face limitations such as delayed bottomhole pressure response and low control precision, particularly under narrow pressure window and complex formation conditions. To address these challenges, Dual-layer Pipe dual-gradient drilling (DGD) technology has been introduced, utilizing a dual-pipe structure and downhole lift pumps to extend the pressure control range. Despite these advantages, current DGD systems lack fast and precise bottomhole pressure control due to their reliance on indirect flow-based methods. This study proposes a bottomhole pressure control method based on backpressure regulation using a hybrid fuzzy-PID control strategy. A dynamic pressure calculation model is developed for the Dual-layer Pipe DGD system, incorporating coupling among choke valve opening, surface backpressure, and bottomhole pressure. The fuzzy-PID controller adjusts valve operation in real-time based on pressure deviation and its rate of change, improving response speed and control accuracy. Simulink-based simulations demonstrate that the proposed system achieves rapid pressure regulation with an overshoot below 5% and steady-state error under 0.12%. Compared to conventional PID control, the fuzzy-PID system shows superior adaptability to pressure variations. This research enhances the theoretical foundation of backpressure control in deepwater DGD operations and provides a practical approach for improving safety and efficiency in complex drilling environments.