| Summary: | Phase velocity and attenuation of guided waves have been estimated from multireceiver,
full waveform, acoustic logging data using the extended Prony's method. Since a formation
affects velocity and attenuation, estimating these quantities is important in evaluating
the formation properties. The estimation is performed using an array processing
technique which requires two steps: (1) the traces for all receivers are transformed into
the frequency domain, and (2) for each frequency the extended Prony's method is used
to determine the presence of a guided wave propagating past the array of receivers. The
guided wave properties estimated by the Prony's method include amplitude, attenuation,
and phase change which is related to phase velocity. An important assumption
in this array processing technique is that the formation, borehole fluid, and tool are
homogeneous along the receiving array. For synthetic data, the phase velocities and attenuation of the tube wave and two modes of the pseudo-Rayleigh wave are accurately
estimated over many frequencies, with the exception that the low amplitude of the second
mode causes its attenuation estimate to be somewhat less accurate. For laboratory
data, very good estimates of the phase velocities of the tube wave and three modes of the pseudo-Rayleigh wave are obtained. Since the materials used in the laboratory
experiment had very large quality factors, the attenuation could not be estimated. For
field data, the dispersion of the tube wave and the velocity of the pseudo-Rayleigh wave
at its cutoff are very close to those predicted by another, independent method. Accurate
attenuation estimates could not be made because the data are noisy and consist of only
eight traces.
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