Monitoring and volumetric estimation of injected CO 2 using 4D seismic, petrophysical data, core measurements and well logging: a case study at Ketzin, Germany

More than 50 000 tons of CO 2 have been injected at Ketzin into the Stuttgart Formation, a saline aquifer, at approximately 620 m depth, as of summer 2011. We present here results from the 1 st repeat 3D seismic survey that was performed at the site in autumn 2009, after about 22 000 tons of CO 2 had been injected. We show here that rather complex time‐lapse signatures of this CO 2 can be clearly observed within a radius of about 300 m from the injection well. The highly irregular amplitude response within this radius is attributed to the heterogeneity of the injection reservoir. Time delays to a reflection below the injection level are also observed. Petrophysical measurements on core samples and geophysical logging of CO 2 saturation levels allow an estimate of the total amount of CO 2 visible in the seismic data to be made. These estimates are somewhat lower than the actual amount of CO 2 injected at the time of the survey and they are dependent upon the choice of a number of parameters. In spite of some uncertainty, the close agreement between the amount injected and the amount observed is encouraging for quantitative monitoring of a CO 2 storage site using seismic methods.