The Genesis of Bit-Induced Torsional Drillstring Vibrations

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Abstract
The work presented here shows that inherent drilling characteristics of PDC bits alone can he sufficient to excite severe torsional drill string vibrations. Lab and field torsional measurements are compared with model results to show that the observed vibrations can be explained by a reduction in PDC bit torque with rotary speed. These torsional vibrations are important because they can cause drill pipe fatigue, and may be severe enough to damage the bit. The model is also used to determine possible solutions to the problem.