Comparing Advanced Control Strategies to Eliminate Stick-Slip Oscillations in Drillstrings

Abstract

In this paper, we present three methods to achieve reliable drillbit angular velocity control for deep drilling operations. We consider a multi-sectional drilling system with the bit off-bottom, which represents the system at the start-up of a drilling operation, e.g., after a connection. The three control procedures are all based on a distributed model for the drilling system. The proposed model has been field validated and considers Coulomb friction between the drillstring and the borehole. The first algorithm we propose combines the industry standard ZTorque controller with a feedforward component. The second procedure is based on a multiplicity-induced-dominancy (MID) design that corresponds to a pole-placement for the downhole state. Finally, the last class of controllers relies on a recursive interconnected dynamics framework. All the controllers are combined with a disturbance rejection procedure whose design is based on a switching-mode approach. These three algorithms are illustrated in simulations with field scenarios on several test-cases. Their complexities, effectiveness and limitations regarding industrial implementation criteria are discussed.

Keywords

• Drillstring vibrations
• stick-slip
• downhole boundary
• bit off-bottom
• distributed systems
• ODE-PDE-ODE system