Algorithm for processing dispersive waves from dipole sonic tool

Abstract

Shear sonic wave velocities can be obtained by monopole sources in logging tools only for fast formations, namely where formation shear velocity is higher than wave velocity in the drilling mud. The dipole source is used for estimating shear velocity in slow formations, by indirectly processing the flexural mode excited in the borehole. The dispersive characteristic of the flexural mode, nevertheless, renders useless the Slowness-Time Coherence method, the traditional algorithm used for processing non-dispersive sonic waveforms from monopole sources. We report the application of Dispersive Slowness-Time Coherence to process sonic log waveforms acquired using dipole sources. This method uses modeled dispersive curves created from classic wave propagation theory and can overcome the previously mentioned limitations. We tested our implementation using real data from four wells drilled in formations with distinct elastic characteristics and found our results compatible to the ones offered by service companies.