Physics of Partially Saturated Porous Media: Residual Saturation and Seismic-Wave Propagation

In this paper, we present a review of seismic-wave propagation in fluid-saturated and partially saturated porous media. Seismic-wave velocity and attenuation are affected by the degree of saturation and the spatial distribution of fluids within the medium. Attenuation mechanisms include local and global flow as well as energy loss caused by scattering. We also present results from acoustic tomography of unconsolidated porous media with residual paraffin saturation. The acoustic attenuation was found to be sensitive to the grain- and subgrain-scale (microscale) distribution of residual saturation; in other words, the residual saturation behaves like soft cement that locally stiffens grain contacts and creates heterogeneity that results in scattering. The effect of microscale phenomena on multigrain scale (macroscale) measurements of seismic-wave attenuation and velocity cannot be ignored.