EFFECT OF PROCESS DAMPING ON LONGITUDINAL VIBRATIONS IN DRILLSTRINGS

This paper shows the effect of process damping-caused by the interfere nce between the cutter and the previously cut surface-on the stability of drillstrings. The method of including process damping in the calcu lation of the stability diagram is outlined. Previously published stab ility diagrams of drillstrings equipped with drag bits showed decrease d stability at low cutting speeds, and that the addition of a shock ab sorber decreased the size of stability pockets. In this paper, we show that the introduction of process damping confirms field observations of increased stability at low speeds. We also show that a properly des igned shock absorber produces largest ability pockets where drilling i s most effective.