Axial and torsional self-excited vibrations of a distributed drill-string

Ulf Jakob F. Aarsnes, Nathan van de Wouw

Research output: Contribution to journalArticleAcademicpeer-review

Abstract

We consider a distributed axial-torsional drill-string model with a rate-independent bit-rock interaction law to study the occurrence and non-local characteristics of axial and torsional self-excited vibrations as caused by the regenerative effect. A first contribution of the paper is the derivation of a non-dimensional version of the full non-linear distributed drill-string–bit-rock interaction model and showing how it relates to the minimal set of characteristic quantities. Using this model the study shows how multiple axial modes of the drill-string are excited, or attenuated, depending on the bit rotation rate. This indicates that a lumped drill-string model approximation is insufficient for the general case. Then, a comprehensive simulation study is performed to create a stability map for the occurrence of stick-slip oscillations. In particular, the significance of the axial topside boundary condition, i.e., constant velocity vs. constant hook-load, is evaluated. A central finding is that increasing the axial loop gain (determined by the bit-rock parameters) tends to both increase the area of stable torsional dynamics and increase the rate of penetration for a constant imposed weight on bit. This also corresponds to a more severe axial instability.

LanguageEnglish
Pages127-151
Number of pages25
JournalJournal of Sound and Vibration
Volume444
DOIs
StatePublished - 31 Mar 2019

Fingerprint

Drill strings
strings
vibration
Rocks
rocks
occurrences
axial modes
Stick-slip
hooks
Hooks
slip
derivation
penetration
Boundary conditions
interactions
boundary conditions
oscillations
approximation
simulation

Keywords

  • Distributed parameter systems
  • Drill-string vibrations
  • Hyperbolic systems
  • Infinite dimensional systems
  • Stability
  • Stick-slip

Cite this

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title = "Axial and torsional self-excited vibrations of a distributed drill-string",
abstract = "We consider a distributed axial-torsional drill-string model with a rate-independent bit-rock interaction law to study the occurrence and non-local characteristics of axial and torsional self-excited vibrations as caused by the regenerative effect. A first contribution of the paper is the derivation of a non-dimensional version of the full non-linear distributed drill-string–bit-rock interaction model and showing how it relates to the minimal set of characteristic quantities. Using this model the study shows how multiple axial modes of the drill-string are excited, or attenuated, depending on the bit rotation rate. This indicates that a lumped drill-string model approximation is insufficient for the general case. Then, a comprehensive simulation study is performed to create a stability map for the occurrence of stick-slip oscillations. In particular, the significance of the axial topside boundary condition, i.e., constant velocity vs. constant hook-load, is evaluated. A central finding is that increasing the axial loop gain (determined by the bit-rock parameters) tends to both increase the area of stable torsional dynamics and increase the rate of penetration for a constant imposed weight on bit. This also corresponds to a more severe axial instability.",
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Axial and torsional self-excited vibrations of a distributed drill-string. / Aarsnes, Ulf Jakob F.; van de Wouw, Nathan.

In: Journal of Sound and Vibration, Vol. 444, 31.03.2019, p. 127-151.

Research output: Contribution to journalArticleAcademicpeer-review

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