Parametric studies on drill-string motions

Experimental and numerical investigations are conducted into drill-string motions. The numerical efforts are carried out by using a reduced-order model with attention to stick-slip interactions between a drill string and an outer shell. These efforts are complemented by experimental studies conducted with a unique, laboratory scale model. Qualitative and quantitative changes in the system behavior are studied with respect to the rotation speed and mass imbalance. Comparisons are made between the numerical findings and the corresponding experimental results. In addition, the influence of contact conditions between the drill string and the outer shell on the drill-string dynamics is also examined. The findings of the work suggest that small changes in the system rotation speed can have a significant influence on the nature of drill-string motions and they also provide guidelines for steering the system out of regions of undesirable dynamics and maintaining drill-string motions close to the center of a borehole. (C) 2011 Elsevier Ltd. All rights reserved.