Understanding High-Frequency Torsional Oscillations HFTO in Rotary Steerable Applications: Observations, Learnings, and Tales of Caution

Abstract

High-Frequency Torsional Oscillations (HFTO) continue to be a challenge for Rotary Steerable System (RSS) Performance. While ruggedization of downhole tools has improved significantly over the years and has enabled tools to survive these violent events, excessive vibrations can still lead to drilling inefficiencies, shortened lifespans of components (increased replacement rates during tool servicing), or occasionally errors in sensor readings. This study shares some key observations during HFTO events including relationships between other vibration modes, behavior with other commercially available vibration mitigation tools, mitigation strategies, and practical limitations. Case histories are presented highlighting HFTO behavior and what this vibration mode looks like within drilling data. Real-time, log, and high-frequency data are all examined to illustrate the differences and variability of each. Mitigation strategies are addressed in detail, looking at parameter adjustments, changes to the Bottom-Hole Assembly (BHA), and different types of dedicated vibration mitigation tools. Benefits and shortcomings are shown for each. Results show the benefit of planning for this type of vibration event and illustrate how the specific drilling application can impact the dynamic response of the BHA. Some unique dynamic characteristics have been observed and are discussed. One such behavior that has been noted is the presence of a torsional beating phenomenon when utilizing a torsional spring-like type of vibration mitigation tool. The physics of this behavior is further examined through detailed modeling and simulation, accurately replicating the observed field measurements. General HFTO observations over the years have also led to the development and implementation of a new at-bit viscous damper type of HFTO mitigation device. Due to the success of this at-bit mitigation device, it has been integrated directly into the Rotary-Steerable System (RSS), removing the need for additional tools or connections in the BHA, and is now a standard technology on all RSS deployments. The data presented in this study is the first documented case of a torsional beating phenomenon during an HFTO event. In addition to this, general HFTO observations are shown in a concise format to share the knowledge gained thus far with this type of vibration. The success resulting from the implementation of the only at-bit HFTO mitigation device is also highlighted.