Velocity Analysis Of Multi-Receiver Full Waveform Acoustic Logging Data In Open And Cased Holes
Name
1986.4 Block et al.pdf
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846.16 KB
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42112f2e02e2e791c766f69904311400
Author(s)
Block, Lisa V.
Cheng, C. H.
Duckworth, Gregory L.
Date Issued
1986
Publisher
Massachusetts Institute of Technology. Earth Resources Laboratory
Series/Report no.
Earth Resources Laboratory Industry Consortia Annual Report;1986-04
Abstract
Average semblance and maximum-likelihood spectral analysis are applied to synthetic
full waveform acoustic logging data to determine formation velocities. Of particular
interest is the ability of these methods to resolve the P wave and pseudo-Rayleigh wave
arrivals in data from poorly-bonded cased boreholes. In open-hole data the velocity
analyses generally yield results within 0.15 km/s of the true velocities. For cased-hole
models with no steel/cement bonding (free pipe), the measured P-wave velocities are
0.2 to 0.6 km/s less than the actual formation velocities, and the S-wave velocities are
within 0.15 km/s of the true velocities. If the P-wave velocity is fairly close to the
plate velocity of the steel pipe (within 0.7 km/s or so), then the P-wave arrival is not
separated from the steel arrival by the semblance method, but the P wave is resolved
by the spectral analysis. For cased-hole models with no cement/formation bonding
(unbonded casing), accurate formation velocities are obtained if the velocities are not
too great. When the formation P-wave velocity approaches the velocity of the casing
arrival, the P-wave resolution is lost by both methods. Further work needs to be done
to better define this limit.
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