We have modeled numerically the seismic response of a poroelastic
inclusion with properties applicable to an oil reservoir that interacts
with an ambient wavefield. The model includes wave-induced fluid
flow caused by pressure differences between mesoscopic-scale (i.e.,
in the order of centimeters to meters) heterogeneities. We used a
viscoelastic approximation on the macroscopic scale to implement
the attenuation and dispersion resulting from this mesoscopic-scale
theory in numerical simulations of wave propagation on the kilometer
scale. This upscaling method includes finite-element modeling of
wave-induced fluid flow to determine effective seismic properties
of the poroelastic media, such as attenuation of P- and S-waves.
The fitted, equivalent, viscoelastic behavior is implemented in finite-difference
wave propagation simulations. With this two-stage process, we model
numerically the quasi-poroelastic wave-propagation on the kilometer
scale and study the impact of fluid properties and fluid saturation
on the modeled seismic amplitudes. In particular, we addressed the
question of whether poroelastic effects within an oil reservoir may
be a plausible explanation for low-frequency ambient wavefield modifications
observed at oil fields in recent years. Our results indicate that
ambient wavefield modification is expected to occur for oil reservoirs
exhibiting high attenuation. Whether or not such modifications can
be detected in surface recordings, however, will depend on acquisition
design and noise mitigation processing as well as site-specific conditions,
such as the geologic complexity of the subsurface, the nature of
the ambient wavefield, and the amount of surface noise.