Control of Stick-Slip Vibration in Drillstrings with Multiple Frequencies

Torsional vibration is a common phenomenon, known as stick-slip in oil-well drilling, that causes poor drilling performance, downhole tool failure, and bit wear. It is observed that stick-slip vibration- generally occur at multiple frequencies. To help mitigate torsional vibration, a dynamic model of drillstring is first studied where analytical solution of torsional vibration is given. Then, a novel model-based controller is proposed to dampen the stick-slip across a wide frequency range. Meanwhile, controller tuning guidelines are provided. The new control-design methods are finally validated by simulations as well as field experiments on a test drilling rig, which demonstrates the advantage of the proposed controller.