An ADRC-based Stick-slip Vibration Control Method for Drill String

Abstract

For complex deep wells, the drill string stick-slip vibration is a intensive destructiveness torsional vibration caused by twisting vibration and down hole drag. This phenomenon can be explained that the bit is motionless for some time, and when the torque on drill string is large enough, the bit suddenly rotate at a high-speed. The stick-slip vibration has become a major problem to be solved urgently in the exploration and exploitation of deep and ultra-deep wells. In drilling operations, the stick-slip will occur in drilling for more than half of the time. Usually, the stick-slip vibration leads to the decrease of penetration rate and the increase of completion cycle. In serious cases, it leads to drill string fracture, bit failure, and even serious downhole accidents. In this thesis, the drill string torsion model is established, the drill string stick-slip vibration mechanical model is proposed, the equation of stick-slip vibration motion is analyzed and the general laws of drill string stick-slip vibration are acquired. In order to effectively suppress stick-slip vibration, an auto-disturbance rejection control (ADRC) method is adopted. Result of experiment shows that the soft-torque control method can make the actual speed of motor changed according to the torque, so as to decrease the motor torque fluctuations, eliminate stick-slip vibration and achieve the drill string soft-torque control.