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Abstract

When CO2 replaces brine as a free gas it is well known to affect the elastic properties of porous media considerably. 3D seismic time-lapse surveys (4D seismics) have proven to be a suitable technique for monitoring of injected CO2. Forward modeling of a 4D seismic response to the CO2 fluid substitution in a storage reservoir is an important step in such studies. In order to track the migration of CO2 at the Ketzin pilot site (Germany), 3D time-lapse seismic data were acquired by means of a baseline (pre-injection) survey in 2005 and the monitor surveys in 2009 and 2012. Results of 4D seismic forward modeling with the reflectivity method suggest that effects of the injected CO2 on the 4D seismic data at the Ketzin pilot site are significant regarding both seismic amplitudes and time delays. They prove the corresponding observations in the real 4D seismic data at the Ketzin pilot site. However reservoir heterogeneity and seismic resolution, as well as random and coherent seismic noise are negative factors to be considered while the interpretation. In spite of these negative factors, results of 4D seismic forward modeling with the reflectivity method support the conclusion that the injected CO2 can be monitored at the Ketzin pilot site both qualitatively and quantitatively.