Observer and reference governor based control strategy to suppress stick-slip vibrations in oil well drill-string

Abstract

The undesired stick-slip vibrations of the drill-string can lead to drilling failures or even serious drilling accidents. Most of previous researches devoted to controller design to reduce such vibrations. However, a characteristic of drilling systems is that only the surface top drive velocity can be measured, which limits the controllers that are used in drilling field. In this paper, a new control strategy is proposed based on a state observer and a reference governor to suppress stick-slip vibrations of the drill-string. The proposed state observer only needs surface measurement and can estimate all states of the drilling system as well as the nonlinear torque between the bit and the rock. According to the estimated nonlinear interaction torque, the reference governor is introduced to modify the original reference input set by the operator. Finally, by simulation, the performance of the control strategy under different nonlinear interaction torque is demonstrated.