High frequency torsional oscillation (HFTO) has gained considerable attention over the past several years due, in large part, to the continued use of motor-assisted Rotary-Steerable Systems. The consequences of such vibration events can be increased repair and maintenance costs, noisy measurements, and/or premature failures. While there are commercial tools available that can provide some relief to the symptoms of HFTO, data gathered thus far does not point to a consistent, reliable, and cost-effective solution to the problem. In light of current HFTO mitigation limitations, a new solution has been developed that shows promise in limiting the HFTO response in the BHA, if not removing it entirely. This new mitigation component is integrated directly into a Rotary-Steerable System. As a result, there are no requirements for additional tooling, connections, or special handling to mitigate these vibrations.
The development of the presented method for mitigating HFTO stems from several years of gathering, and thoroughly analyzing, downhole data captured in a rotary-steerable system run below mud motors. A method for detecting HFTO in real-time is also presented, and the frequency and vibrational pattern of this dynamic phenomenon is confirmed in post-well reviews of high frequency data. Proprietary modeling is used to confirm that the measured frequencies seen downhole are associated with torsional resonant frequencies of the BHA, which is a defining characteristic of this particular vibration mode. A concept is developed for mitigating these types of downhole vibrations, based on the detailed understanding of the vibration characteristics, using a proven approach from outside the industry. Feasibility of this technology is confirmed through extensive vibration modeling. Prototype tools have been built and tested downhole in several US land basins over the past year. The positive results seen during initial field-testing has led to the new HFTO mitigation tool now being a standard technology for motor-assist RSS applications.
Results have shown a consistent reduction in HFTO vibration, both in terms of amplitude and duration. Amplitude reductions between 50-100% have been observed routinely, which has led to a measureable increase in reliability and longevity of components being run below a mud motor. Based on how the mitigation tool is set up, a greater or lesser damping effect is seen in the measured HFTO response. This suggests the mitigation tool can be adjusted for targeted damping in certain scenarios, and may have a benefit in more than just rotary-steerable applications.