90 Well seismic surveying and acoustic logging On the 3 m constant offset acoustic section (Figure 3.6a), we can see the first arrival refracted P-wave, the refracted S-wave and the associated Rayleigh waves in the 1-2 ms time interval, the latter being particularly visible for depths greater than 440 m. Figure 3.6b shows the two 3 and 3.25 m constant offset acoustic sections, in the 0.5-1.1 ms time interval, centered on the refracted P-wave. The Stoneley acoustic waves are visible after 2 ms. It can be noted that the latter have a higher frequency content at depths greater than 440 m. The processing consisted of calculating the VP and VS velocity log, the Poisson’s ratio log, and the refracted P-wave frequency log, using the instantaneous frequency. The different logs are presented in Figure 3.6c and d. a B C Figure 3.7 Example of acoustic data processing. a): 3m constant offset acoustic section b): Velocity log (waves) and correlation log. Low values of velocity and correlation coefficient indicate the presence of karstic levels. c): P-waves amplitude log. The very small amplitudes indicate the presence of karstic levels.
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