Research on drill string stick-slip vibration and its soft-torque control

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. In this thesis, drill string torsion model is established, drill string stick-slip vibration mechanical model is proposed and the equation of stick-slip vibration motion is analyzed. After this, the general laws of drill string stick-slip vibration are acquired and the control scheme of drill string soft-torque control system is proposed. 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.