Monitoring and volumetric estimation of injected CO₂ using 4D seismic, petrophysical data, core measurements and well logging: a case study at Ketzin, Germany

Abstract

More than 50000 tons of CO 2 have been injected at Ketzin into the Stuttgart Formation, a saline aquifer, at approximately 620 m depth, as of the summer 2011. We present here results from the 1 st repeat 3D seismic survey that was performed at the site in the autumn 2009, after about 22000 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 CO 2 storage site using seismic methods.

Quantitative evaluation of thin-layer thickness and CO2mass utilizing seismic complex decomposition at the Ketzin CO2storage site, Germany

“…The chosen frequency correctly corresponds to the first tuning frequency and allows mapping of the reservoir tuning frequency (Fig. 8) the sandstone unit ranges from 50 to 80 Hz, corresponding to a two-way temporal thickness between 6.3 and 10 ms. Ultrasonic laboratory experiments indicate an average velocity of the reservoir sandstone saturated with 100 per cent formation brine at the Ketzin site of 3135 m s −1 (Ivanova et al 2012). Therefore, the calculated thickness of the reservoir based on the tuning frequency ranges from 9.7 to 17.4 m, consistent with the 9-20 m sandstone unit derived from well logs .…”

“…Using H = VT/2, where V is reservoir velocity and T is the two-way temporal thickness, the corresponding thicknesses (H) of the gaseous CO 2 plume at the two repeat times at the Ktzi 201 well correspond to 21.7 and 23.3 m, both close to the net thickness of the reservoir sandstone but slightly higher. This is reasonable since pulsed neutron-gamma logging had detected the presence of CO 2 within a thinner siltstone and sandstone layer underlying the main injection interval in the Ktzi 201 well (Ivanova et al 2012;Baumann et al 2014).…”

“…In autumn 2005, a 3-D seismic survey, serving as a baseline, was acquired (Juhlin et al 2007), followed by two 3-D repeat seismic surveys (Ivanova et al 2012;Ivandic et al 2015) volume in order to minimize the non-injection related anomalies (Ivanova et al 2012;Ivandic et al 2015). Fig.…”

“…In addition, if CO 2 leaks into the overlying formations, quantitative estimation of CO 2 leakage is required for designing the most effective remediation and mitigation strategies (Ivanova et al 2012). However, several limiting factors, like thin layers and limited vertical resolution exist, making quantitative seismic analysis difficult at CO 2 storage sites.…”

Monitoring of environmental influences on seismic velocity at the geological storage site for CO2 in Ketzin (Germany) with ambient seismic noise

“…They are visible on all station combinations and on all components. The injection of CO 2 into a porous layer changes the medium and lowers the seismic velocities with respect to a reference state before the injection (Eiken et al 2000;Kazemeini et al 2010;Ivanova et al 2012). Therefore, we expect a monotonic decrease of the seismic velocities over the period of the injection because the injection is almost continuous with a constant rate (on average).…”