Frequency Analysis of Surface and Downhole Dynamics Demonstrates Effectiveness of Impedance Matching Torsional Damping System Across Multiple Drillstring Harmonics

Abstract Torsional vibration, commonly referred to as ‘stick-slip’ is one of the most common modes of drillstring vibration, often driving lateral and axial shocks as the BHA accelerates in the ‘slip’ phase. Higher harmonics of torsional vibration can be particularly troublesome to overcome by conventional methods of parameter adjustments to preserve tool and bit life while optimizing drilling performance. Impedance Matching Torsional Damping Systems (IMTDS) can dampen a wide range of frequencies from the drillstring, by means of removing the reflective boundary at surface. This paper demonstrates the effectiveness of an IMTDS at mitigating a range of frequencies, including higher harmonics from the drillstring. Previous studies have examined changes in measured downhole RPM statistics (Max/Min/Mean/RMS) while turning the IMTDS on and off during drilling. This paper dives deeper to pull out specific frequencies present in the drillstring from downhole dynamics recorders, and their change in magnitude with IMTDS activated. Drillstring modelling is also conducted to tie the recorded dominant frequencies to the first, second, third, or fourth harmonics of the drillstring. Data collected throughout multiple wells with various pipe sizes at a broad range of depths with IMTDS both on and off reveals multiple torsional harmonics being drastically dampened when the system is turned on. Drillstring modelling shows these frequencies corresponding to the first to fourth harmonics of the drillstring. For further validation, frequency analysis was conducted on data collected from the Top Drive VFD and correlated to BHA frequencies for a holistic analysis of the entire system. This paper demonstrates real-world applications of the IMTDS effectively dampening multiple harmonics of torsional vibration across a wide depth range from vertical to horizontal sections, on pipe sizes from 4" to 5 ½", with both conventional and RSS assemblies. Detailed analysis of frequency domain draws out the natural frequencies of the drillstring and demonstrates how the IMTDS can be used to effectively mitigate a broad range of torsional vibration in many applications.