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Torsional dynamics can be extremely damaging to downhole drilling tools and can significantly affect drilling efficiency. Industry focus on combating this has led to the development of various downhole mitigation tools, improved bit technologies, BHA designs and better management of drilling parameters. The aforementioned focus primarily on combating stick-slip, or at least the conventional form of it, with its distinctive stick and slip phases. This paper outlines two lesser known types of torsional dynamics observed whilst drilling inter-bedded carbonate formations in the middle-east with the latest generation in point-the-bit Rotary Steerable Systems (RSS). One of these phenomena has the potential to be extremely damaging, more so than conventional stick-slip, and is of such high frequency that conventional logging rates are incapable of detecting it. This paper highlights the presence of a low frequency ( This paper outlines findings from both field and laboratory tests, attempting to better understand both the low and high frequency torsional phenomenon. This paper goes one step further than existing literature by attibuting the high frequency torsional oscillations to structural resonances within the BHA. This is substantiated both analytically and experimentally. Understanding the underlying characteristics of these phenomena paves the way for new, more effective, prevention systems. The paper concludes with the development of a unique sensor which monitors subtle changes in the industry standard Stick-slip Index to detect different torsional dynamic modes in realtime and send a text based description and severity rating to surface. |
