Evidence of chatter and its dependence on stability of drillstrings equipped with PDC bits

摘要

A great deal of theoretical work has been performed on chatter in drillstrings equipped with Plycrstalline Diamond COmpact (PDC) bits. In this paper we present a theoretical model of the system which is used to analyze chatter characteristics, such as its frequency and correlation to bit diameter and speed. We also present chatter measurement in laboratory tests performed on Berea Sandstone and Sierra White SGranite, as representatives of soft and hard rocks respectively. In both cases, it was shown that chatter severity correlates well with lack of system stability based on theoretical predictions. We also show that the phenomenon of "mode hunting" can be explained using chatter theory. An understanding of chatter leads to improved bit designs and the choice of drilling parameters most conducive to minimum chatter.