Abstract
We investigate complex drill-string dynamics in a downhole drilling where strong nonlinear interactions between various types of vibration take place. First, we present a low dimensional model of the downhole drilling where a drill-bit cutting a rock formation has a strong coupling between torsional and axial oscillations. The model can be used to study drilling stability as an example results are given. Then we introduce a new experimental rig developed by the Centre for Applied Dynamics Research at the University of Aberdeen, capable of reproducing all major types of drill-string vibration. One of the most important features of this versatile experimental rig is the fact that commercial drill-bits, employed in the drilling industry, and real rock-samples are used. The rig operate in different configurations, which enables the experimental study of various phenomena, such as stick-slip oscillations, whirling and drill-bit bounce. It also allows to determine mechanical characteristics of the drill-bits, which are used to calibrate mathematical models.
Highlights
Dynamics of drill-strings belongs to one of the most challenging modelling problems and has been the subject of intensive research for many years
Nonlinear nature of the interactions between a drill-string and a bottom hole assembly (BHA) and their borehole, generates complex coupled vibration with its axial, torsional and lateral components. This dynamic behaviour being a result of the borehole creation and various frictional and geometrical effects along a drill-string and a BHA, makes the problem difficult to study in a comprehensive manner
This process is controlled by many parameters including Weigh On Bit (WOB) and rotary speed
Summary
Dynamics of drill-strings belongs to one of the most challenging modelling problems and has been the subject of intensive research for many years. Nonlinear nature of the interactions between a drill-string and a bottom hole assembly (BHA) and their borehole, generates complex coupled vibration with its axial, torsional and lateral components This dynamic behaviour being a result of the borehole creation and various frictional and geometrical effects along a drill-string and a BHA, makes the problem difficult to study in a comprehensive manner. We focus our attention on axial and torsional vibration via a fully coupled two degrees-of-freedom model with a state-dependent time delay. Contrary to majority of published work, the dynamic loading of the drill-bit reflect both the cutting and frictional effects occurring during a wellbore creation process This process is controlled by many parameters including Weigh On Bit (WOB) and rotary speed. It indicates a new stable region for low rotational speed and relatively high WOB, which was not reported previously
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