Suppression of drill-string stick–slip vibration by sliding mode control : Numerical and experimental studies

Peer reviewedPostprin

Numerical and experimental studies of stick-slip oscillations in drill-strings.

The cyclic nature of the stick-slip phenomenon may cause catastrophic failures in drill-strings or at the very least could lead to the wear of expensive equipment. Therefore, it is important to study the drilling parameters which can lead to stick-slip, in order to develop appropriate control methods for suppression. This paper studies the stick-slip oscillations encountered in drill-strings from both numerical and experimental points of view. The numerical part is carried out based on path-following methods for non-smooth dynamical systems, with a special focus on the multistability in drill-strings. Our analysis shows that, under a certain parameter window, the multistability can be used to steer the response of the drill-strings from a sticking equilibrium or stick-slip oscillation to an equilibrium with constant drill-bit rotation. In addition, a small-scale downhole drilling rig was implemented to conduct a parametric study of the stick-slip phenomenon. The parametric study involves the use of two flexible shafts with varying mechanical properties to observe the effects that would have on stick-slip during operation. Our experimental results demonstrate that varying some of the mechanical properties of the drill-string could in fact control the nature of stick-slip oscillations

Fluid induced drilling dynamics: A mechanically scaled experimental investigation

Drillstring vibration is an unavoidable detrimental dynamic response due to continuous acting external forces and dynamic loading applied during the drilling operations. Drillstring vibration is one of the primary reasons behind downhole equipment malfunctioning and premature fatigue failure. Laboratory scaled experiments gained much popularity to investigate the physics of induced vibrations by replicating the downhole vibrations phenomena, due to their economic design and versatility. The majority of laboratory scaled experiments oftentimes are only scaled geometrically and address isolated phenomena. Thus, most downscaled investigations provide limited insight and cannot relate to the overall dynamics of field conditions. The objective of this work is to design and fabricate a fully functioning mechanically scaled experiment and fulfill the experimental lacking of fluid hydrodynamic effects on drillstring vibrations. The developed experimental setup is equipped with a high-frequency vibration measurement system and the capability to capture the BHA trajectory. The setup was used to investigate the effect of WOB fluctuation on lateral motion and the effect of fluid flow on drillstring stability

EXPERIMENTAL INVESTIGATION OF THE EFFECTS OF ROTATIONAL SPEED AND WEIGHT ON BIT ON DRILLSTRING VIBRATIONS, TORQUE AND RATE OF PENETRATION

Experimental investigation was carried out on an automated drilling rig fabricated for the Drillbotics competition. The effects of rotational speed and weight on bit were observed on drillstring vibrations, torque and rate of penetration for two different sandstone samples

Experimental study of the D-OSKIL mechanism for controlling the stick-slip oscillations in a drilling laboratory testbed

International audienceThe presence of harmful stick-slip oscillations in oil well drillstrings has attracted the attention of the control community in recent years. The control law named D-OSKIL mechanism which uses the weight on the bit (WoB) force as an additional control variable to extinguish limit cycles has been investigated. This paper reports experimental implementation of such a mechanism, in a laboratory testbed. We also provide details of the experimental process and the obtained drilling performance. Results show that the stick-slip oscillations can be effectively suppressed by this mechanism