A Study of Slip/Stick Motion of the Bit

Abstract

This paper deals with torsional oscillations caused by slip/stick motion of the drill-collar section. This phenomenon is associated with a large-amplitude, saw-tooth-like variation in the applied torque. "Slip/stick motion" refers to the belief that the amplitude of the torsional oscillations becomes so large that the drill-collar section periodically comes to a complete stop and does not come free until enough torque is built up in the drillstring to overcome the static friction.A mathematical model of slip/stick motion is presented. This model includes parameters describing downhole friction effects and a simplified description of the drillstring. The effects of damping, finite rotary-table inertia, and the rotary-speed control system are discussed. Theoretical predictions are compared with measured torque signals recorded during field drilling.This kind of drilling performance is likely to be less effective than normal drilling and may also lead to fatigue problems. This paper discusses ways to avoid severe torsional oscillations by using a more sophisticated feedback system to control the rotary speed.

Derivation and experimental validation of an analytical criterion for the identification of self-excited modes in drilling systems

“…It can be stated from Eqs. (14) and (15) that the value of S c;i generally increases with the natural angular frequency ω 0;i ¼ πi=L ffiffiffiffiffiffiffiffi ffi G=ρ p or the number of the mode shape i if the modal damping factor D i is equal for all mode shapes. The equation is independent of the length L of the torsional oscillator.…”

“…Several studies have focused on stick/slip of the whole drilling system, the most familiar kind of measured torsional vibration [11,14,15]. In this context, the drilling systems comprises the rig, a drillstring, and a bottomhole assembly (BHA) with measurement tools, and a bit to cut the formation.…”

On the development of high-frequency torsional impact drilling techniques for hard formation drilling

“…Dawson et al 3 used a simple torsional pendulum to study stick-slip motion of the bit. Attempts to reveal the stick-slip phenomenon and its characteristics via torsional pendulum models were done by Kyllingstad and Halsey, 4 Lin and Wang, 5 Yigit and Christoforou, 6 and Richard et al 7,8 As reported in the literature, [9][10][11] the stick-slip performances and impact factors are investigated to search for controlling schemes of this vibration. In the meanwhile, measurement while drilling is used to optimize the drilling parameters to reduce stick slip.…”

Adaptive Torsional Tuned Vibration Absorber for Rotary Equipment

“…Upon determining the critical speeds of drill strings, recommendations were set to execute drilling operations at speeds below the lowest critical speed to avoid resonance. This demonstration drives the need for a novel solution to attenuate the vibrations in the drill string, even while running close to critical speeds to maintain the optimum efficiency of drilling.Halsey et al [16] proposed a torque feedback control algorithm to minimize the stick-slip motion. The concept was to allow the rotary table speed to dampen the vibrations in the drill string by attenuating the reflections of the torsional waves.…”

“…Halsey et al [16] proposed a torque feedback control algorithm to minimize the stick-slip motion. The concept was to allow the rotary table speed to dampen the vibrations in the drill string by attenuating the reflections of the torsional waves.…”