Drill Bit Whirl Mitigation Analysis – An Under Actuated System Perspective

Lateral vibrations are the most destructive type of vibrations affecting rotary drilling.They are recognized by a phenomenon popularly known as drill bit whirl.The major causes leading to drill bit whirl are identified as the effect of a bend drill string or a manufacturing unbalance in the drill bit.This paper presents a detailed analysis of the drill bit whirl phenomenon by laboratory tests on a rotary drilling prototype built for the purpose.Practical methods which could control or limit these vibrations below the damaging threshold values are discussed in this paper.The paper also presents an explanation of the under actuation of the drill bit and hence its complex control objectives.A few typical under actuated system control solutions are presented, to analyze the scope of applying similar techniques to the drill bit whirl problem.