Managed-Pressure Drilling: Using Model Predictive Control To Improve Pressure Control During Dual-Gradient Drilling

Abstract

Summary Managed-pressure drilling (MPD) offers unprecedented capabilities for precise pressure control in drilling operations. This capability, created by the availability of new hardware tools, creates the need for tight coordination of such tools, to ensure reliable and safe operation. The use of model predictive control (MPC) is proposed as a multivariable control framework that can coordinate multiple variables to offer both better performance and higher reliability and safety compared with current practice. A case study on a dual-gradient drilling system is presented to demonstrate how MPC can simultaneously control bottomhole pressure and hook position during drillstring movement, by simultaneously manipulating the main-pump flow rate, seabed-pump flow rate, and drillstring velocity. Simulations focusing on the robustness to modeling errors and noise sensitivity will also be presented. Computer simulations show that the proposed approach results in much lower bottomhole-pressure (BHP) deviations during drillstring movement than manual control of hook position alone. The sensitivity to errors in the MPC model and noise are found to be low. The implications of this study as well as future directions for integration of additional variables and use of appropriate MPC variants are discussed.