Active and Passive full waveform acoustic logging: a field test case

Two boreholes of an experimental site located in the the Cher region (France) were investigated via full waveform acoustic logging (FWAL). The acoustic tool used for the FWAL experiments is a flexible monopole tool holding two pairs of piezoelectric receivers and a magnetostrictive transducer. The tool has been modified to perform both active and passive FWAL. To our knowledge, such a change is a novelty. For passive acoustic logging, several runs have been recorded to obtain a set of acoustic noise sections. Noise root mean squared (RMS) amplitude logs and spectral amplitude logs in different frequency bandwidths have been computed. The acoustic logs resulting from passive acoustic monitoring have been compared with P-wave acoustic velocity, core data and flowmetry. It is shown that: 1- the distribution of noise frequencies in the 0 -5 kHz are strongly correlated with the variations of the flowmeter, 2-the distribution of noise frequencies and noise RMS amplitude are correlated with the lithology (core description) and the P-wave velocity log.