Dynamic instabilities of the bottomhole assembly (BHA) such as whirl, stick/slip, and bit bounce have been the focus of the majority of research studies in drilling vibrations. Recently, elevated levels of high-frequency rotational vibrations were recorded in the field with a high-bandwidth downhole vibration monitoring device. New experimental and numerical insights into this relatively unexplored phenomenon of high-frequency torsional oscillations are presented and discussed in this paper.

A suite of laboratory and field tests were conducted to understand and characterize the phenomenon. Computer modeling with in-house drillstring dynamics software corroborated well with the field measurements and validated the research team approach.

The investigation concluded that the drilling process excites BHA torsional vibrations. These vibrations occur at much higher frequencies than drill collar resonance and are significantly dependent on the drilled formation. New insights are gained into drilling dynamics in general and high-frequency torsional oscillations in particular.

The paper presents worldwide field case studies to illustrate the phenomenon. Details are provided of testing where the drilling environment is strategically controlled to characterize the dependence of these high-frequency torsional oscillations on bit design, operating parameters, and formation properties. The implications on drilling performance are also discussed in an attempt to satisfy the quest for efficient and reliable drilling.

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