High-Frequency Torsional Dynamics of Drilling Systems: An Analysis of the Bit-System Interaction

Abstract

Recent advances in downhole vibration monitoring have enabled detection of high-frequency torsional oscillations (HFTO) of drilling systems in the field. The general understanding of torsional behavior of drilling systems derived from elaborate efforts in the literature does not explain the mechanism responsible for HFTO. Even for the well-known and extensively studied stick/slip vibrations, the mechanism perpetuating the vibrations is not agreed upon by researchers. The paper discusses findings from experimental and analytical studies regarding the HFTO of bottomhole assemblies (BHAs). The phenomenon is investigated and reproduced in field tests, full-scale laboratory tests, and computer modeling. Drilling conditions are identified in which the drilling system is prone to exhibit the vibrations. Interaction of the bit and the drilling system, which can generate self-excited vibrations, is investigated using analytical methods. Cutter-rock interaction as a possible excitation source is studied using laboratory experiments to elucidate its interaction with the system. The integrated analysis investigating rock, cutter, bit, and BHA interaction identifies HFTO as a bit-induced BHA torsional resonance that can occur at vibration modes higher than the fundamental mode of the BHA. It is demonstrated that modes most susceptible to exhibiting HFTO can be identified and the dominant mode predicted. The understanding gained can be employed to mitigate torsional resonance and enhance drilling performance.

A New Model of High-Frequency Torsional Oscillations (HFTO) of Drillstring in 3-D Wells

“…Despite small backlash in the spindle, the axial connection of the stator and the shaft can be considered almost absolutely rigid assuming that for the purpose of axial oscillations analysis the BHA is a continuous rod, which is elastic at axial deformation. This assumption is supported by the analysis of the field data of torsional and axial oscillations of the drillstring with the positive displacemen motor [10]. At the same time, the stator-rotor connection under torsional oscillations is not direct but through gearing.…”

“…In recent years downhole measurements revealed high-frequency torsional oscillations of the order of hundreds of hertz with sufficiently great amplitude [10,14]. It is considered that these oscillations propagate within the BHA for comparatively short distance.…”

“…Frequency characteristics of these oscillations will depend not only on inertia and stiffness characteristics of the BHA in general but also on the inertia characteristics of the downhole motor. Till now the dynamics of the PDM has not been considered when studying HFTO [10,13], and for this reason it was not always possible to adequately evaluate the quantitative characteristics of these oscillations [10,13].…”

The Application of Downhole Vibration Factor in Drilling Tool Reliability Big Data Analytics—A Review

“…(1) Most analytics based on FRBD focuses on individual reliability characteristics or failure criteria, while drilling tools have more than one failure modes simultaneously caused by vibration together with other downhole factors. Therefore, it is necessary to link and analyze downhole vibration data with multiple downhole factors, coupled failure modes, and physics-based models of drilling tools interactively, emphasizing on the failure mode with greater cost impact [36]. Model and predict the system reliability [4,7] Utilizes predictive life models and real-time data to optimize operation and maintenance decision-making.…”

A Method for the Design and Optimization of Nonlinear Tuned Damping Concepts to Mitigate Self-Excited Drill String Vibrations Using Multiple Scales Lindstedt-Poincaré

“…Due to improved and new measuring tools, high-frequency oscillations have been identified as the cause of numerous drill string failures and have been intensively investigated over the last years with studies [9,10], simulations [8,11] and experiments [12,13]. Especially drilling in hard and dense formations leads to highfrequency torsional oscillations (HFTO) with frequencies between 50 Hz and 500 Hz [14,15].…”