Along String Dynamics Measurements Reveal Isolated Potentially Damaging Upper String Vibration Environments

Abstract

Abstract While dynamics studies of drilling Bottom Hole Assemblies (BHAs) have been common since the introduction of downhole vibration measurement tools, little attention has been given to the dynamic environment in the upper drill string. By using distributed recorded mode dynamic subs both in the BHA and higher in the drill string, it has been possible to identify dynamic dysfunctions in the drill string that are not evident from BHA based sensors. This paper examines offshore wells from the North West Shelf, Australia and the North Sea, which exhibit these potentially damaging vibrations. Data was collected from the downhole measurement tools and merged with surface data to allow the investigation of the BHA and drill string dynamic environments. In addition, high speed data bursts were investigated to understand the finer details of the dynamics. Modelling of the BHA and string to predict the critical vibration modes, resonances and contact forces was also carried out. The analysis of the wells showed that while the bottom hole assemblies displayed very little torsional or lateral vibration; the upper drill string components were exposed to high energy lateral vibrations. The high energy lateral vibration environments were typically either bound by the rig drive system and contact forces between the drill string and the cased hole or between localized high contact forces in the upper sections of the well. Contact forces can isolate the drill string into distinct dynamic environments, potentially creating high energy destructive events in one section while relatively normal conditions are maintained in the other sections. These isolated drill string dynamic dysfunctions can potentially lead to accelerated drill pipe or casing wear with no obvious cause. This paper shows how using distributed dynamics sensors throughout the BHA and drill string enables a detailed view of the drilling dynamics in the upper drill string, which previously has only been discussed theoretically. The study also highlights the potential risk for accelerated wear to both drill pipe and casing.