Drillstrings develop vibrations when run at critical rotary speeds, and these vibrations are
difficult to control due to the strings’ long length and large mass. Operating at a critical speed imparts severe shock and vibration damage to the drillstring, fatigues drill collars and rotary connections. Vibrations also cause the drillstring to lift off bottom, reducing ROP. The effect of axial, lateral and torsional (stick-slip or bit whirl) vibration upon drilling have been documented
in both the laboratory2 and the field2
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