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H ig h F re q ue nc y


1 3 1 1


P 9 7 5 5 3 3 1 1 0 2 4 0 5 Time, ms X D ip ol e


1 3 1 1


9 9 0 7 7 0 2 4 6 8 F requency, kH z 5 5 3 3 1 1 0 5 1 0 Time, ms 1 5 2 0 0 5 1 0 Time, ms


>Waveform s ( left) from a fast form ation offshore Norw ay . Monopole transm itters ( top) at high freq uencies ( left) generate clear P-, S-and Stoneley w aves, and low freq uencies ( right) generate m ostly Stoneley w aves. Flex ural w aveform s generated b y the dipole transm itters ( b ottom ) are recorded on the X ( left) and Y ( right) receivers. Dispersion analy sis ( right) show s slightly dispersive Stoneley data, highly dispersive  ex ural data and nondispersive shear data. The com pressional w ave is ex cited only at freq uencies higher than 8 k Hz in this form ation, and is not show n on the dispersion curve. [ Modi ed from Pistre et al, reference 3 ( SEG) . ]


1 5 2 0


1 3 1 1


Y D ip ol e 1 0 0 Shear 1 0 Time, ms 1 5 2 0 2 0 0 Flex ural 3 0 0 Stoneley S 9 Stoneley 7 4 0 0


1 3 1 1


L ow F re q ue nc y


H ig h F re q ue nc y


1 3 1 1


9 9 7 7 5 5 3 3 1 1 0 2 4 6 0 Time, ms F a st F l e x ura l 1 1 9 9 7 7 5 5 3 3 1 1 0 1 0 Time, ms 2 0 3 0 0 1 0 Time, ms


>Waveform s ( left) from a slow form ation in the USA. The high-freq uency m onopole source ( top left) generates no shear w ave and sm aller Stoneley w aves than in the fast-form ation case. At low freq uency , the m onopole source ( top right) generates predom inantly Stoneley w aves. The X - and Y -dipole transm itters generate low -freq uency  ex ural w aves com pared w ith the fast form ation. Anisotropy in this form ation causes  ex ural-w ave splitting, creating a fast and slow  ex ural w ave ( b ottom leftand right, respectively ) . The low -freq uency dispersion data ( right) include the Stoneley m ode and tw o  ex ural m odes. Higher freq uency dispersion analy sis of the P-w ave data reveals dispersion— lab eled leak y com pressional— at higher freq uencies. [ Modi ed from Pistre et al, reference 3 ( SEG) . ]


2 0 3 0 1 7 0 1 5 0 0 2 4 6 8 F requency, kH z Com pressional 1 1 1 9 0 S l ow F l e x ura l 1 0 Time, ms 2 1 0 2 0 3 0


1 3 1 1


9 0 0 8 0 0


7 0 0


6 0 0 5 0 0


0 1 2 3 F requency, kH z


Leak y com pressional


Flex ural Fast shear Stoneley Slow shear


L ow F re q ue nc y


Spring 2006


17


R eceiver number


R eceiver number


R eceiver number


R eceiver number


Slowness, µs/ ft


Slowness, µs/ ft


Slowness, µs/ ft


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