Nonlinear observer-based control of unstable wells

This paper presents a nonlinear observer-based control scheme applied to stabilize riser induced slugging. A simple empirical model is developed that describes the qualitative behavior of the downhole pressure in case of severe riser slugging. A nonlinear observer is developed for estimation of unmeasured states. The developed controller is designed by an integrator backstepping approach to stabilize the downhole pressure and eliminate riser slugging. Stabilization in the unstable region is demonstrated, and it is shown that the proposed controller not only can guarantee global stability, but also transient performance. Simulation results are presented to illustrate the effectiveness of proposed control scheme.