Continuous Mapping of P Wave Velocity Dispersion - A Useful Tool for Reservoir Characterization

For reservoir rocks, P wave velocity dispersion may provide a potential link to rock physical properties. This requires continuous measurement of P wave velocity in a broad frequency band to determine the critical frequency of the attenuation mechanism. In this study, we measure P wave velocity dispersion continuously in sonic frequency range using broadband full-waveform multi-channel sonic logging data with the beam-forming and cross-correlation techniques. Results of the field data from 5L-38 Mallik gas hydrate research well have demonstrated the robustness of this method. The profile of P wave velocity dispersion matches very well with geological settings. The gas hydrate zones show very strong P wave velocity dispersion and a pronounced critical frequency around 15 kHz; weakly-laminated sediments also have strong P wave velocity dispersion with critical frequency lower than 5 kHz; P wave velocity dispersion in consolidated sediments is mild and gradual. In addition, the total magnitude of P wave velocity dispersion is positively correlated to resistivity and gas hydrate saturation. Therefore, continuous P wave velocity dispersion mapping can be a promising tool for reservoir characterization.