Drillstring-borehole interaction: backward whirl instabilities and axial loading

Abstract

A major concern within the oil drilling industry remains the high risk associated with the drilling bit and tool failure from the build-up of damaging vibrations. Effective understanding of the drillstring dynamics is essential for efficient drilling operation. Complex dynamic behaviour is often observed in the drillstring due to friction, impact, unbalance eccentricity and energy exchange between different modes of vibrations. The interaction between the drillstring and borehole wall involves nonlinearities in the form of friction and contact. Initially a two discs model was developed to analyse the behaviour of the system. The theoretical model was tuned by altering the phase of the eccentric mass. This excites each lateral modes of the system in isolation. The effects of impact, friction and mass unbalance are included in the model. The drillstring borehole interaction induces whirling behaviour of the drillstring causing forward whirl, backward whirl or intermittent bouncing behaviour depending on the system parameters. A critical steady state behaviour within the system is the backward whirling of the drillstring, which reduces the fatigue life of the drillstring. For the tuned system the backward whirl behaviour was analysed by carrying out a rotor speed sweep spanning the lateral natural frequencies. The influence of rotor speed on the system dynamics is explored using a run up and run down and is analysed using a waterfall plot. The waterfall plot indicated the frequency of maximum response corresponding to each

Non-linear modal interactions during rub-impact of a rotating flexible shaft

“…The amplitude of higher order lines are observed. This is due to the backward whirl which is observed at (r/δ)Ω Hz, where r is the radius of the rotor and δ is the clearance (Vijayan et al (2014); Chipato et al (2021)). The diameter of the stator used in the experimental test rig is 14.5 mm, resulting in (r/δ)Ω=7.…”

“…Drillstring experiences axial, torsional and transverse vibrations during the time of operation. Various authors have tried to model the drillstring behaviour using the lumped parameter model (Yigit and Christoforou (2000); Vijayan et al (2017, 2014)), finite element (Khulief and Al-Naser (2005)) and cosserat rod theory (Wang et al (1999)). The vibration modes and their interactions cause different dynamic effects such as bit bounce, stick slip, and forward and backward whirl on the drillstring.…”

Dynamic Model and Quantitative Analysis of Stick-Slip Vibration in Horizontal Well

“…us, friction and impact may occur between the drillstring and the borehole. In this paper, elastic force is employed to describe the friction between drillstring and borehole wall [24]. e elastic forces in the y and z directions can be given as…”

Nonlinear coupled motions of a pipe-in-pipe system experiencing vortex-induced vibrations

“…Vlajic et al [13,14] made significant efforts in studying the Jeffcott rotor system with torsional vibrations in the presence of continuous stator contact, aiming at reducing the system DOFs and analyze the coupling between backward whirl motions and torsional vibrations. Vijayan et al [15] developed lateral-torsional coupled drill string models with double and five disks, finding that under stable contact-induced backward whirl states, the backward whirl frequency dominates the system instead of the driving frequency.…”