Abstract

Borehole acoustic tools that use broadband source excitation functions can optimally excite multiple frequencies at nearly the same time, yielding a wide range of different formation acoustic response properties in the received signal. However, the analysis of received broadband signals is not straightforward in the time-domain because standard time semblance algorithms suffer from interference when received acoustic modes with different slownesses and frequency content arrive at a similar time. Another method, frequency semblance, is computationally expensive and is sensitive to noise and to other effects. We propose using specially designed phase filters that can move (delay) individual frequency contributions differently in time without changing the spectral amplitudes of the received signal, thus enabling existing time semblance methods to perform optimally at many frequencies by separating the received spectra in time.

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