Cross-axis control system design for borehole drilling based on damping optimum criterion and utilization of proportional-integral controllers

Abstract

This paper presents a control system design methodology for the drill-string rotary drive and draw-works hoist system aimed at their coordinated control for the purpose of establishing a fully-automated mechatronic system suitable for borehole drilling applications. Both the drill-string rotary drive and the draw-works hoist drive are equipped with proportional-integral (PI) speed controllers, which are readily available within modern controlled electrical drives. Moreover, the rotary speed control system is equipped with torsional active damping system and drill-string back-spinning prevention scheme for the case of stuck drill-bit scenario, whereas the draw-works-based drill-bit normal force control system is extended with the auxiliary control system aimed at timely prevention of the drill-string torsional overload. The design of proposed control systems has been based on suitable reduced-order control-oriented process models and a practical tuning methodology based on the damping optimum criterion aimed at achieving the desired level of closed-loop system damping. The functionality of the proposed cross-axis control system has been systematically verified, first by experimental tests of individual rotary/vertical axis control systems on a downscaled laboratory experimental setup, followed by thorough simulation study of the overall control system for realistic scenarios encountered in the field.