METHOD AND APPARATUS FOR OSCILLATING A DRILL STRING

摘要

A method of oscillating a drill string (135) , which method comprises the steps of : (a) rotating said drill string (135) in a first direction until a first limit is reached; and (b) rotating said drill string (135) in a seco nd direction until a second limit is reached; characterised in that said fir st and second limits are based upon the amount of energy expended during rot ation .