Manipulation of the choke pressure during Managed Pressurized Drilling (MPD) operation

Abstract

In the present investigation, the disturbance and its effect on the bottom hole pressure has been studied. After digging into the prior works, it’s figured out that the reason of their failure is oversimplification and ignoring some parameters that have considerable impact on the BHP like frictional forces resulting from fluid and drill string movements. Following the weakness of the last studies, the feasibility of applying new hydraulic model has been studying and new assumptions have been presented. The model is provided by a set of linked PDEs 1. the pressure dynamics of the well annulus during unsteady Couette flow with a pressure gradient; 2. The movement of the elastic drill string coupled with the pressure dynamic through viscous friction and displacement of drilling mud. It is shown how the model can be simplified to a linear system and under which assumption this simplification can be proceeded. By using the Laplace transformer and inserting appropriate boundary conditions, the transfer function is derived from the linear system. The resulting model uses heave disturbance and controlled flow into the wellbore as input, and the measured pressure at the top of the well, as well as the pressure at the bottom of the well as output. Based on the Hydraulic model developed, for the sake of simplification and faster running time, a lower order of the model with fewer control volumes have been introduced for the Model Predictive Controller (MPC). Two control algorithms for both normal and intervention operations have been evolved by application of PID and Model Predictive Controller (MPD). The Optimization of the PID controller has been done theoretically and validified by MATLAB.