We studied the seismic attenuation and velocity dispersion effects
produced by wave-induced fluid flow in weakly consolidated sandstones
containing patchy carbon dioxide (CO(2))-brine distributions. The
analysis also focuses on the velocity pushdown because of the presence
of this gas, as well as on the role of the wave-induced fluid flow
(mesoscopic) effects on the amplitude variation with angle (AVA)
seismic response of thin layers containing CO(2), such as those found
at the Utsira Sand, Sleipner field, offshore Norway. We found that
this loss mechanism may play a key role on conventional surface seismic
data, suggesting that further data analysis may provide useful information
on the characteristics of the fluid distributions in these environments.
Numerical experiments let us observe that although mesoscopic effects
can be very significant in this kind of media, the seismic response
of a given isolated thin layer computed considering such effects
is very similar to that of a homogeneous elastic thin layer with
a compressional velocity equal to that of the original porous rock
averaged in the effective data bandwidth. This suggests that the
thin-bed prestack spectral inversion method published by the authors
could be used to estimate representative compressional velocities
and layer thicknesses in these environments. In effect, results using
realistic synthetic prestack seismic data show that isolated CO(2)-bearing
thin beds can be characterized in terms of their thicknesses and
representative compressional velocities. This information can be
qualitatively related to CO(2) saturations and volumes; thus, the
prestack spectral inversion method could find application in the
monitoring of the evolution of CO(2) plumes at injection sites similar
to that at the Sleipner field.