TY - JOUR
T1 - Axial and torsional self-excited vibrations of a distributed drill-string
AU - Aarsnes, Ulf Jakob F.
AU - van de Wouw, Nathan
PY - 2019
Y1 - 2019
N2 - 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.
AB - 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.
KW - Distributed parameter systems
KW - Drill-string vibrations
KW - Hyperbolic systems
KW - Infinite dimensional systems
KW - Stability
KW - Stick-slip
UR - http://www.scopus.com/inward/record.url?scp=85059543383&partnerID=8YFLogxK
U2 - 10.1016/j.jsv.2018.12.028
DO - 10.1016/j.jsv.2018.12.028
M3 - Article
AN - SCOPUS:85059543383
SN - 0022-460X
VL - 444
SP - 127
EP - 151
JO - Journal of Sound and Vibration
JF - Journal of Sound and Vibration
ER -