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Torsional Dynamics and Point-the-Bit Rotary-Steerable Systems

Torsional dynamics can be extremely damaging to downhole drilling tools and can significantly affect drilling efficiency. The effort to prevent this phenomenon has led to the development of various downhole mitigation tools, improved bit technologies and bottomhole-assembly (BHA) designs, and better management of drilling parameters. This paper outlines two lesser-known types of torsional dynamics observed while drilling interbedded carbonate formations in the Middle East with the latest generation in point-the-bit rotary-steerable systems (RSSs).

Introduction

Aspects of dynamic behavior considered to be particularly undesirable include the following:

  1. Large fluctuations of bit-rotation rate (ω) and the often-associated amplitude modulation of higher-frequency vibrations. [These features are usually ascribed to stick/slip behavior, wherein ω is periodically zero, then much larger than the rotation rate at surface (Ω). Potentially, stick/slip could also occur at positions in the drillstring other than the bit.]
  2. Backward whirl, where the bit rolls around the (enlarged) borehole in a sense opposite to Ω.

Resonances of the drill-string may drive or be driven by Items 1 and 2; enlarged or irregularly shaped boreholes are likely to be involved.

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 163428, “Torsional Resonance: An Understanding Based on Field and Laboratory Tests With Latest-Generation Point-the-Bit Rotary Steerable Systems,” L.A. Lines, SPE, D.R.H. Stroud, SPE, and V.A. Coveney, Weatherford, prepared for the 2013 SPE/IADC Drilling Conference and Exhibition, Amsterdam, 5–7 March. The paper has not been peer reviewed.
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Torsional Dynamics and Point-the-Bit Rotary-Steerable Systems

01 December 2013

Volume: 65 | Issue: 12

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