In this work we analyze how patchy distributions of CO2 and brine
within sand reservoirs may lead to significant attenuation and velocity
dispersion effects, which in turn may have a profound impact on surface
seismic data. The ultimate goal of this paper is to contribute to
the understanding of these processes within the framework of the
seismic monitoring of CO2 sequestration, a key strategy to mitigate
global warming. We first carry out a Monte Carlo analysis to study
the statistical behavior of attenuation and velocity dispersion of
compressional waves traveling through rocks with properties similar
to those at the Utsira Sand, Sleipner field, containing quasi-fractal
patchy distributions of CO2 and brine. These results show that the
mean patch size and CO2 saturation play key roles in the observed
wave-induced fluid flow effects. The latter can be remarkably important
when CO2 concentrations are low and mean patch sizes are relatively
large. To analyze these effects on the corresponding surface seismic
data, we perform numerical simulations of wave propagation considering
reservoir models and CO2 accumulation patterns similar to the CO2
injection site in the Sleipner field. These numerical experiments
suggest that wave-induced fluid flow effects may produce changes
in the reservoir's seismic response, modifying significantly the
main seismic attributes usually employed in the characterization
of these environments. Consequently, the determination of the nature
of the fluid distributions as well as the proper modeling of the
seismic data constitute important aspects that should not be ignored
in the seismic monitoring of CO2 sequestration problems.