Model-Based Control in Managed Pressure Drilling

Abstract Increased use of Managed Pressure Drilling (MPD) has enabled a significant improvement in drilling operations through the ability to accurately control pressure within a narrow window and by actively managing the annular pressure profile. However, the technology has not yet reached its full potential; well control events involving a gas influx causes two-phase flow in the well and can lead to severe deterioration of pressure control performance. In this study, a robust model-based MPD control system is presented and results from drilling a well in the Umm al-Quwain region in the UAE demonstrate invaluable benefits for both normal operations and during well control events. Due to its transient nature, drilling has always been a complicated operation and requires highly skilled personnel to achieve the desired pressure control accuracy. The introduction of automated MPD systems tries to implement more robust and safer control over well control operations that were previously manual tasks, however, this is still a challenge since wellbore conditions are constantly changing. This has prompted the need for proactive and model-based control techniques that act in advance to optimize the performance based on measurements and knowledge of the system. The development of this state-of-the-art MPD control system involved detailed validation in a high-fidelity simulator and thorough tests of robustness and performance in a full-scale flow loop with continuous gas injection capabilities, with focus on two-phase flow and gas influx handling. Results from field operations show that the model-based MPD control system maintains robust performance during planned operations such as connections and drilling ahead. Based on pump flow measurements surface back-pressure or bottom hole pressure are maintained constant during fast pump ramp-down and ramp-up without the use of a back-pressure pump. Usually, MPD control systems require strict procedures on pump ramp speed to maintain constant pressure during transient operation. In this paper, the model-based control system implemented is shown to handle irregular pump flow changes and still maintain constant surface back-pressure or bottom hole pressure. In particular, a simulated pump emergency shutdown is shown where the pumps are stopped in less than 20 seconds. The MPD control system still managed to maintain constant bottom hole pressure by closing the chokes in a controlled manner. In summary, this paper presents a field implementation of a fully model-based MPD control system that demonstrates its ability to compensate for irregular pump flow changes. Throughout these irregular pump flow changes, the control system maintains constant bottom hole pressure or surface back-pressure. Furthermore, the system demonstrates the ability to maintain the desired pressure control precision in all normal operations and during all unplanned events experienced during the operation.