ABSTRACT
When a mesoscopically or locally heterogeneous porous medium is subjected to an external disturbance, fluids in different regions respond with different pressures, resulting in local fluid flow (Pride et al. 2003). Consequently, the macroscopic capillary pressure is generally a dynamic quantity. The local flow induced by a stress wave dissipates wave energy, resulting in intrinsic wave attenuation and velocity dispersion (velocity depending upon frequency). Such acoustical signatures play a key role in determining the characteristics of local flow and dynamic capillarity. A visco-poroelastic model that is capable of characterizing the relaxation processes associated with local fluid flow has been developed (Wei & Muraleethanan 2006). Given the measured acoustical data, specifically the velocity and attenuation of the compressional wave, the model can be used to determine the characteristic time of local flow. Since local flow is governed
by the details of local heterogeneities, the obtained characteristic times can in turn be used to infer the information on local heterogeneities, and their effects on macroscopic fluid flow through the dynamic capillary pressure saturation relationship (or water retention relationship) which is described in the next section.
