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Research Papers

Drill-String Dynamics: Reduced-Order Models and Experimental Studies

[+] Author and Article Information
Chien-Min Liao

Department of Mechanical Engineering, University of Maryland, College Park, MD 20742-3035gimmy@umd.edu

Balakumar Balachandran1

Department of Mechanical Engineering, University of Maryland, College Park, MD 20742-3035balab@umd.edu

Mansour Karkoub

Department of Mechanical Engineering, Texas A&M University-Qatar Branch, Doha, Qatarmansour.karkoub@qatar.tamu.edu

Youssef L. Abdel-Magid

Department of Electrical Engineering, Petroleum Institute, P.O. Box 2533, Abu Dhabi, UAEyabdelmagid@pi.ac.ae

1

Corresponding author.

J. Vib. Acoust 133(4), 041008 (Apr 08, 2011) (8 pages) doi:10.1115/1.4003406 History: Received March 14, 2010; Revised November 25, 2010; Published April 08, 2011; Online April 08, 2011

In this article, reduced-order models of a drill-string system are developed, the predictions of these models are studied, and qualitative comparisons are made with experimental studies. The reduced-order models allow for radial, bending, and torsion motions of a flexible drill string and stick-slip interactions between the drill string and an outer shell. Qualitative changes in the system motions are studied with respect to the rotation speed of the drill string and the friction coefficient between the drill string and the outer shell. The nonlinear motions predicted by the model are in agreement with the experimental observations, and these studies suggest that there may be preferred friction coefficient values for which most of the drill-string motions occur close to the center of a borehole. These modeling and experimental studies can serve as an important basis for furthering our understanding of drill-string dynamics and schemes for controlling them.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Representative schematic of a rotary drill rig

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Figure 2

Illustration of two section model

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Figure 3

Schematic of model with four degrees of freedom

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Figure 4

Schematic of Sec. 2 used in model with four degrees of freedom

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Figure 5

Schematic of Sec. 2 used in model with five degrees of freedom

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Figure 6

Schematic of model with five degrees of freedom

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Figure 7

Illustration of contact scenarios between drill string and outer shell: (a) two contact scenarios, (b) rotation with no sliding, and (c) pure sliding with no rotation

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Figure 8

Phase portrait projections for motions around equilibrium point of the 4DOF model: (a) lateral direction: initial position close to the origin, (b) lateral direction: initial position close to the outer shell (boundary), (c) lateral direction: initial position on the boundary, (d) tangential direction: initial position close to the origin, (e) tangential direction: initial position close to the boundary, and (f) tangential direction: initial position on the boundary

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Figure 9

Phase portrait projections for motions around equilibrium point of 5DOF model: (a) lateral direction: initial position close to the origin, (b) tangential direction: initial position close to the origin, (c) lateral direction: initial position close to the outer shell (boundary), and (d) tangential direction: initial position close to the boundary

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Figure 10

Comparison of polar plots of rotor trajectories: (a) current work: friction coefficient of 0.1, (b) current work: friction coefficient of 0.3, (c) current work: friction coefficient of 0.9, (d) Ref. 5: friction coefficient of 0.1, (e) Ref. 5: friction coefficient equals of 0.3, and (f) Ref. 5: friction coefficient of 0.9

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Figure 11

Phase portraits and time histories: ((a) and (d)) results for friction coefficient of 0.1, ((b) and (e)) results for friction coefficient of 0.3, and ((c) and (f)) results for friction coefficient of 0.9. The dashed vertical line in the phase plots corresponds to the outer shell.

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Figure 12

Time history of tangential motion component: (a) complete record and (b) a portion showing slipping and sticking

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Figure 13

Experimental arrangement: (a) whole assembly, (b) motor and controller, (c) top disk with encoder, and (d) bottom disk with encoder

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Figure 14

Schematic of experimental setup in side view and top view

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Figure 15

Experimental observation of rotor motions illustrating bouncing and rolling contact: (a) bouncing motion (left to right and top to bottom) and (b) rolling motion (left to right and top to bottom)

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Figure 16

Numerical simulation of rotor motions corresponding to experiment showing segments of rolling contact in (b) and bouncing contact in (c)

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