On the effective control of torsional vibrations in drilling systems

This paper analyses a control mechanism designed to significantly ameliorate the sustained excitation of torsional relaxation oscillations (slip-stick) due to frictional torques generated by an active bit during drilling operations with an extended drill-string. The proposed mechanism of torsional rectification is compared with existing soft-torque devices in a series of mathematical models. Both analytic and numerical simulations indicate that many of the volatilities suffered by existing soft-torque feedback approaches used to combat slip-stick can be eliminated by the alternative proposed here. © 1999 Academic Press.