High-Frequency Torsional Dynamics of Drilling Systems: An Analysis of the Bit-System Interaction

Abstract

Abstract Recent advances in downhole vibration monitoring have enabled detection of high-frequency torsional oscillations (HFTO) of drilling systems in the field. The general understanding of torsional behavior of drilling systems derived from elaborate efforts in the literature does not explain the mechanism responsible for HFTO. Even for the well-known and extensively studied stick/slip vibrations, the mechanism perpetuating the vibrations is not agreed upon by researchers. The paper discusses findings from experimental and analytical studies regarding the HFTO of bottomhole assemblies (BHAs). The phenomenon is investigated and reproduced in field tests, full-scale laboratory tests, and computer modeling. Drilling conditions are identified in which the drilling system is prone to exhibit the vibrations. Interaction of the bit and the drilling system, which can generate self-excited vibrations, is investigated using analytical methods. Cutter-rock interaction as a possible excitation source is studied using laboratory experiments to elucidate its interaction with the system. The integrated analysis investigating rock, cutter, bit, and BHA interaction identifies HFTO as a bit-induced BHA torsional resonance that can occur at vibration modes higher than the fundamental mode of the BHA. It is demonstrated that modes most susceptible to exhibiting HFTO can be identified and the dominant mode predicted. The understanding gained can be employed to mitigate torsional resonance and enhance drilling performance.