Precession of Rotary Drillstrings Should be Eliminated

Abstract

SUMMARY Results obtained using a scale model of several hundred metres of a drill string are presented. The model has shown that the rotary drilling process is dominated by precession of the drill string. The nature of this motion is explained, along with its relationships to bending stress and torque. It is suggested that high speed precession contributes significantly to bending fatigue of drill strings; and eliminating the precession is the approach to prolong the service lives of rotary drill string components and to carry out high speed safe drilling.