Nonlinear Model-Based Control of Unstable Wells

This paper illustrates the potential of nonlinear model-based control applied for stabilization of unstable flow in oil wells. A simple empirical model is developed that describes the qualitative behavior of the down hole pressure during severe riser slugging. A nonlinear controller is designed by an integrator back stepping approach, and stabilization for open-loop unstable pressure set points is demonstrated. The proposed back stepping controller is shown in simulations to perform better than PI and PD controllers for low pressure set points, and is in addition easier to tune. Operation at a low pressure set point is desirable since it corresponds to a high production flow rate. The simulation results are presented to illustrate the effectiveness of proposed control scheme.