A PHENOMENOLOGICAL STUDY OF FRICTION INDUCED TORSIONAL VIBRATIONS OF DRILL STRINGS
Master of Science
The problem of drill string vibrations when the bit is off the bottom is addressed. It is asserted that these vibrations cannot be rationalized on the basis of linear vibration theory. The central surmise is that nonlinearity in friction induces oscillations. Plausible models for friction are propounded. Two distinct types of motion are detected, with and without stickslip. Numerical and analytical procedures are employed to solve the governing differential equation of a free-sliding, single degree of freedom system with dry friction. The results are compared with data procured at three rigs. Their close correlation substantiates the principal contention of the study.