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《Chinese Journal of Geophysics》 2016-09
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Radiation characteristics of the single-well imaging field in while-drilling logging using an acoustic dipole source

CAO Jing-Ji;TANG Xiao-Ming;SU Yuan-Da;WEI Zhou-Tuo;ZHUANG Chun-Xi;COSL-UPC Allied Borehole Acoustic Laboratory,School of Geosciences & Technology,China University of Petroleum(East China);  
Sing-well dipole acoustic imaging has recently emerged as an important geophysical well-logging technology to detect geologic structures several tens of meters away from a borehole.With growing needs in the logging while-drilling(LWD)environment,the application of this technology has received much attention.Compared with wireline logging,the LWD acoustic measurement is made up of a drill collar that occupies a large part of the borehole,which significantly influences the performance of the dipole acoustic source mounted on the drill collar.Thus a systematic study is needed to analyze the radiation characteristics of the LWD dipole source for the single-well imaging application.In this study,we analyze the elastic wavefield of an LWD dipole source.The wavefield consists of guided waves along the borehole and the radiated elastic waves into the formation.Using the wavefield solution,we calculate the sourcegenerated energy flow along the borehole and the energy flow away from the borehole into the formation.The ratio of the latter to the former defines the radiation efficiency of the LWDsource.In conjunction with shear-wave imaging,we also study the radiation and reflection of SHand SV-waves for the LWD condition.Our analysis shows that the energy flow characteristics and radiation efficiency of the LWD source are strongly affected by the drill collar.Relative to the wireline modeling result,the SH-and SV-wave radiation efficiency in LWD is reduced by 70%,and the optimum radiation frequency band is shifted to 2.5kHz from its wireline counterpart of3.5kHz.Apart from these marked differences between LWD and wireline conditions,our modeling shows that an LWD shear-wave reflection survey in the optimum frequency band can still detect reflection signals from reflectors information.Our theoretical results can be used to provide a useful reference for the design and development of an LWD dipole acoustic imaging tool.
【Fund】: 国家自然科学基金(41474092);; 中央高校基本科研业务费专项资金(15CX06003A)资助
【CateGory Index】: P631.81
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