Hydrocarbon bearing reservoir rocks often contain a mixture of several fluids in their porespace (e.g. oil, water and gas). If the pore fluids are immiscible and form pockets on a mesoscopic length scale (exceeding the typical pore size but still small compared to seismic wavelength), the fluid saturation is referred to as patchy saturation. Elastic waves travelling through such a rock will exhibit a characteristic frequency-dependent attenuation and velocity dispersion. These dynamic effects are believed to contribute significantly to the overall characteristics of the seismic wavefield. We numerically simulate wave propagation in a partially saturated rock model containing water with gas inclusions and extract attenuation and dispersion from synthetic seismograms. The results are compared to a theory of frequency-dependent attenuation and velocity dispersion in partially saturated media. Our numerical results are in reasonable agreement with those predicted theoretically. Furthermore, we are able to accurately infer information about the size of the patches from the extracted frequency-dependent attenuation. This underlines the possibility that the size of the fluid patches can be estimated from seismic data.


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