Control and estimation of downhole pressure in managed pressure drilling operations

This paper presents a nonlinear adaptive observer and a simple model-based control scheme to stabilize the annular pressure profile throughout the well bore continuously while drilling. A simple mechanistic model is presented that captures the dominant phenomena of the drilling system and forms the basis for model-based observer and control design. A new nonlinear adaptive observer is developed for estimation downhole pressure. A simple PI controller is designed to stabilize the annular pressure and achieve tracking by applying feedback control of the choke valve opening and the main pumps.