Experimental full-waveform sonic datawere collected in an exploration well penetrating unconsolidated sand-shale sequences. Using a low frequency (2,000 Hz) compressional wave source drive, formation compressional (P) wave arrivals were recorded in acoustically-slow, gas bearing sands. In some intervals formation velocities were slower than the borehole fluid speed. Standard (10,000 Hz) P-wave acquisition failed to detect formation signals across the same intervals. Shear wave acquisition was accomplished using dipole transducers. Interpretation of the measured V_P/V_S ratio highlighted gasbearing intervals where the V_P/V_S ratio dropped below the background compaction trend.
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