Phase velocity and attenuation of guided waves have been estimated from acoustic loggingdata recorded by a receiving array. The method uses data from multiple sourcesand successive depths yielding more accurate estimates than could be obtained withdata from one source and one depth. The inversion requires two steps: (1) all traces aretransformed into the frequency domain with a fast Fourier transform, and (2) at eachfrequency a modification of Prony's method is used to estimate the guided waves' characteristics which include amplitude, attenuation coefficient, and wavenumber (whichyields the phase velocity). An important assumption underlying this technique is thatthe formation, borehole fluid, and tool are homogeneous along the receiving array.Application of this method to synthetic data shows that the phase velocity and attenuation of the tube and pseudo-Rayleigh waves are accurately estimated at manyfrequencies. With noisy synthetic data, the phase velocities are correctly determined,but the attenuation estimates, being sensitive to noise, are accurate only when the amplitudes are high. Using data from multiple sources and successive depths suppressesthe noise effects and improves both estimates. The amplitude estimates are importantbecause they roughly indicate the reliability of the velocity and attenuation estimates.From laboratory and field data, the velocities for the guided waves are accurately predicted even when the amplitudes are low. The attenuation estimates are good whenthe amplitudes are high but degrade as the amplitudes diminish.
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