Boundary Control and Estimation for Underbalanced Drilling With Uncertain Reservoir Parameters

In underbalanced drilling (UBD), the bottom hole pressure is kept below pore pressure, causing pressure-dependent influx of reservoir gas into wellbore that makes system unstable at low drawdowns. this article, we propose a feedback controller which stabilizes system, represented by “reduced drift flux model (DFM),” around an arbitrary setpoint, while using only topside measurement and assuming unknown parameters. A particular challenge with problem distributed highly nonlinear nature dynamics, where DFM” models gas–liquid flow as transport equation nonlocal integral source term. An observer estimates concentration, downhole parameters solving dynamics backward relative to how rises in well. The control inputs are then constructed designing target states over next sampling period again reversed obtain required pressures. resulting implemented 2-min zero-order hold accommodate actuation limitation situation on actual rig. Finally, results illustrated simulations industry standard formulation plant model.