Nonlinear Model Predictive Controller for Kick Attenuation in Managed Pressure Drilling*

We propose a new design of nonlinear model predictive controller (NMPC) for automatic control of managed pressure drilling (MPD) system. The proposed controller acts in a pressure control mode and tracks bottom-hole-pressure (BHP) set point during normal operations, and automatically switches to a flow control mode in the event of abnormal situations, i.e. gas kick. It contains kick, when it occurs, within certain threshold by the deft use of nonlinear state constraints. We use output feedback control architecture and employ offset-free NMPC algorithm which utilizes recursive-discretization for discretization of the model and use active set method for optimal control calculation. We demonstrate that the proposed controller is able to track a bottom hole pressure set point and contain influx in the presence of measurement noise and plant model mismatches.