Rejecting pressure fluctuations induced by string movement in drilling*

Keeping the pressure within predefined bounds is essential for the safety of managed pressure drilling operations, but drill string movements can induce pressure fluctuations that violate these margins. We extend previous results on disturbance rejection for a 2 x 2 hyperbolic model of the fluid dynamics in the borehole. We perform a simulation study, in which we illustrate the controller performance for heave induced oscillations and compare it to the previously available controller. The stochasticity of sea waves induces limitations on the achievable performance. Further, the controller is applied to intended string movements, where control can be used to remove conservative limitations on the speed of the movement.