Measuring and Controlling Torsional Vibrations and Stick-Slip in a Viscous-Damped Drillstring Model

Failure of drillstring components due to torsional stresses are caused by torsional vibrations. This paper<br>investigates the response of the drillstring to torsional vibrations through analysis on an elemental stepped-shaft<br>drillstring model in a damped medium. The paper directs its analysis to the stick-slip motion which is the most<br>common form of torsional vibrations in drillstrings; stick-slip motion is defined as the continuous stopping and<br>release of the bit/BHA due to the irregular downhole rotation prompted by the existing relationship between the<br>frictional torque and the torque applied from the surface to free the bit.