Fuzzy controller design for constant bottomhole pressure drilling under operational/physical constraints

This paper deals with the constant bottomhole pressure as one of the common techniques in Managed pressure drilling (MPD), a complex nonlinear process that employs various control strategies to regulate the bottomhole pressure. To have an accurate operation, the nonlinear controllers usually consider the exact model of the system, which leads to a complex structure that sophisticates their practical implementation due to resulting high computational load. In addition to low computational load, control methods must take into account physical/ operational constraints to be implemented in practice. Utilizing the T-S fuzzy modeling approach as well as the idea of the parallel distributed compensation, this paper constructs a simple fuzzy controller based on the system's exact model and proposes the stabilization criteria in the form of linear matrix inequalities. These criteria not only guarantee the system stability but also satisfy the available physical/operational limitations in the drilling process. We then introduce an optimization problem to obtain the controller gains and find the largest space in which the proposed controller ensures both operational restrictions and stability. The simulation results demonstrate that if the initial condition of the drilling process begins within the margins of the pore and fracture gradients, the bottomhole pressure converges to the desired reference value while the pressure window is not violated and the actuator is not saturated. Thanks to the unsaturated controller during the drilling process and also due to the inherent capabilities of fuzzy logic, in the proposed method, convergence occurs earlier than traditional methods while there is less steady-state error.

Automated summary

This paper proposes a simple fuzzy controller based on the T-S fuzzy modeling approach and the parallel distributed compensation idea, which guarantees the stability of constant bottomhole pressure and operational limitations in the drilling process through linear matrix inequalities.