Coda-wave interferometry analysis of time-lapse VSP data for monitoring geological carbon sequestration Page: 4 of 28
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and attenuation, which result in changes in seismic-wave scattering and propagation. The
changes in seismic velocities are believed to be associated jointly with changes in fluid saturation
(CO2 replacing water and oil) and in pressure (increase in pore pressure due to the injection
process) (Harris et al., 1996). Wang et al. (1998) investigated the effect of CO2 floods on the
seismic velocities in a carbonate rock (dolostone). They found that compressional-wave (P-
wave) velocity Vp decreases from a minimum 3.0% to as high as 10.9%, while shear-wave (S-
wave) velocity Vs decreases from 3.3% to 9.5% as the reservoir rocks are flooded with CO2
under in-situ conditions. Their results show that the combined effects of pore pressure buildup
and fluid substitution caused by CO2 flooding make it feasible to monitor the CO2 flood process
and to map the flooded zones seismically. Rock and fluid physics measurements and modeling
suggest that CO2 can cause a 4-6% decrease in Vp with a corresponding 15-20% change in
reflection amplitude. Time-lapse surface seismic and vertical seismic profiling (VSP) surveys for
monitoring CO2 sequestration also showed changes in P-wave and S-wave velocities due to CO2
injection and strong reflections from injection regions (Arts et al., 2004; Daley et al., 2007).
Time-lapse crosswell tomograms show P-wave reductions of more than 10% in some formations
within the reservoir zone and some changes are as large as 20% (Harris et al., 1996, Daley et al,
2007).
The usefulness of temporal changes, however, is limited by the accuracy and precision with
which velocity measurements can be made (Poupinet et al., 1984; Roberts et al., 1992, Sneider et
al., 2002). Poupinet et al., (1984) introduced the coda-wave interferometry method for estimating
nonlinear behavior in seismic velocity. It has been applied to different studies, such as probing
the relative location of seismic sources (Snieder and Vrijlandt, 2005), monitoring of rapid4
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Zhou, R.; Huang, L.; Rutledge, J. T.; Fehler, M.; Daley, T.M. & Majer, E. L. Coda-wave interferometry analysis of time-lapse VSP data for monitoring geological carbon sequestration, article, November 1, 2009; Berkeley, California. (https://digital.library.unt.edu/ark:/67531/metadc1015000/m1/4/: accessed April 25, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.