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Research Papers: Petroleum Engineering

Vibration Analysis of a Drillstring in Vibration-Assisted Rotary Drilling: Finite Element Modeling With Analytical Validation

[+] Author and Article Information
Ahmad Ghasemloonia

Ph.D. Candidate
e-mail: a.ghasemloonia@mun.ca

D. Geoff Rideout

Associate Professor
e-mail: g.rideout@mun.ca

Stephen D. Butt

Professor
e-mail: sdbutt@mun.ca
Advanced Drilling Group,
Faculty of Engineering,
Memorial University,
St. John's, NL, A1B 3X5, Canada

Contributed by the Petroleum Division of ASME for publication in the Journal of Energy Resources Technology. Manuscript received August 31, 2012; final manuscript received December 18, 2012; published online March 25, 2013. Assoc. Editor: W. David Constant.

J. Energy Resour. Technol 135(3), 032902 (Mar 25, 2013) (18 pages) Paper No: JERT-12-1200; doi: 10.1115/1.4023333 History: Received August 31, 2012; Revised December 18, 2012

Introducing sources of axial vibration into an oilwell drillstring has the potential to improve the drilling efficiency. Vibration generator tools, such as drillstring agitators, are under development or in current use to excite the bottom-hole assembly (BHA) axially in order to increase power and weight at the bit, improve the rate of penetration (ROP), reduce drillstring-wellbore friction, and accelerate the cutting removal process. Enhanced drilling under the effect of intentional imposed vibration is called “vibration-assisted rotary drilling” or VARD. While potentially enhancing the drilling process, VARD tools can also excite many unwanted vibration modes of the drillstring. These unwanted vibrations can cause fatigue damage and failure of BHA components such as “measurement while drilling” (MWD) tools, bit and mud motors, and consequently, inefficient drilling. This motivates a study of the complex dynamic behavior of an axially excited drillstring. Transverse vibration is the most destructive type of drillstring vibration, and the coupling between transverse and axial vibration of a drillstring subjected to an applied VARD force is of great interest to the experts in the field. In this study, the coupled axial-transverse vibration behavior of the entire drillstring under the effect of a VARD tool is investigated. A dynamic finite element method (FEM) model of the vertical drillstring assuming a multispan BHA is generated and validated with a coupled nonlinear axial-transverse elastodynamic mathematical model. The effects of mud damping, driving torque, multispan contact and spatially varying axial load are included. Geometry, axial stiffening and Hertzian contact forces are sources of nonlinearity in the model. A mesh sensitivity analysis is conducted to reduce computational time. The accuracy of the retained modes in the analytical equations is verified by extracting the total effective mass derived by the FEM model. There is agreement between the FEM and analytical models for coupled-transverse and axial vibration velocities, displacements, resonance frequencies and contact locations and behavior. While the analytical model has fast running time and symbolic solution, the FEM model enables easy reconfiguration of the drillstring for different boundary conditions, inclusion of additional elements such as shock subs, and changing the number and locations of stabilizers.

Copyright © 2013 by ASME
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References

Figures

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Fig. 1

Schematic of the multispan drillstring under the effect of the VARD tool

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Fig. 2

Schematic of a three-span BHA

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Fig. 3

Spatially varying axial force along the drillstring

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Fig. 4

Axial deflection near the hook point

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Fig. 5

Axial deflection of a point on the top span

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Fig. 6

Axial deflection of a point on the middle span

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Fig. 7

Axial deflection of a point on the last span, close to the bit

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Fig. 8

Axial velocity of a point on the last span, close to the bit

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Fig. 9

Phase plane, a point on the last span, close to the bit

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Fig. 10

Lateral deflection and velocities for a point on the pipe section

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Fig. 11

Phase plane, phase trajectory and radial deflection for a point on the pipe section

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Fig. 12

Radial deflection of the contact point, first span

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Fig. 13

Radial deflection of the contact point, second span

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Fig. 14

Radial deflection of the contact point, third span

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Fig. 15

Lateral velocities of a point on the top span

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Fig. 16

Normalized total effective mass in each direction

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Fig. 17

Mesh sensitivity analysis, pipe section

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Fig. 18

Mesh sensitivity analysis, collar section

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Fig. 19

The first four mode shapes of a three-span BHA

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