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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