Measurement and Analysis of Stick-Slip Characteristics of Drill String in Ultra-Deep Wells

Complicated stick-slip vibration might induce drilling tool failure and negatively impact drilling efficiency. Much research has been conducted on the mechanisms that cause the generation of such a vibration but they have not been able to arrive at a confirmed conclusion. In this paper, we present a study in which we used ESM drill string vibration measuring devices and tri-axial accelerations of a downhole drill string in an ultra-deep well.Through the analysis of tri-axial acceleration, the stick-slip vibration features of the drill string were reviewed. Research results showed that massive stick-slip vibration occurred in the concerned interval with a stick-slip frequency of 0.11 Hz, period of 9.0 s and a total stick time up to 4.0 s. During the slip stage, the maximum rotation speed of the downhole drill strings reached 330.0 r/min, approximately 2.75 times higher than that on the ground surface; Generally speaking, the stick-slip vibration was in accordance with fluctuations in surface torque. In other words, features of surface torque might be used for preliminary determination of stick-slip vibration of drill string in the borehole. Analysis of frequency show that stick-slip frequencies of radial acceleration were in accordance with the highest amplitude in energy during stick-slip. There were also horizontal resonance frequency and external exciting frequency generated by drilling string contact with the sidewall. But stick-slip frequencies of axial vibrations corresponded well with minor energy amplitudes. In conclusion, the stick-slip of the drill string may be characterized by torsional vibration. At the same time, there were intensive horizontal vibration and relatively weak axial vibrations. This study can provide as reference in stick-slip vibration characterization and removal strategy for eliminating it in ultra-deep wells drilling.