Controlling torsional vibrations of drill strings via decomposition of traveling waves |
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Authors: | Email author" target="_blank">E?KreuzerEmail author M?Steidl |
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Institution: | (1) Ivano-Frankovsk National Technical University of Petroleum and Gas, Ivano-Frankovsk, Ukraine;(2) Ivano-Frankovsk Sector of the Podstrigach Institute of Applied Problems of Mechanics and Mathematics, National Academy of Sciences of Ukraine, Ivano-Frankovsk, Ukraine; |
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Abstract: | Torsional vibrations in drill strings, especially stick-slip vibrations, are detrimental to the drilling process as they slow
down the rate of penetration and may lead to failure of the drilling equipment. We present a method for controlling these
vibrations by exactly decomposing the drill string dynamics into two traveling waves traveling in the direction of the top
drive and in the direction of the drill bit. The decomposition is derived from the wave equation governing the string vibrations
and is achieved with only two sensors that can be placed directly at the top drive and at a short distance below the top drive
(e.g., 5 m). Therefore, downhole measurements along the string and at the bit are not necessary, which is a major advantage
compared to other control concepts for drill string dynamics. The velocity of the top drive is then controlled in order to
absorb the wave traveling in the direction of the top drive, thus achieving a reflection coefficient of zero for the frequency
range of the undesired torsional vibrations. The proposed algorithm is implemented for both a numerical example and an experimental
setup; results show that the control concept works very effectively. |
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