Experiences with a Permanently Installed Seismic Monitoring Array at the CO2 Storage Site at Ketzin (Germany): A Status Overview

Since July 2008, CO2 is injected into a saline aquifer near the town of Ketzin in Germany. For monitoring the CO2- migration close to the injection well, TNO installed a fixed 2D seismic array of 120 meters length in 2009, with 3- component geophones at the surface, 4-component receivers at 50 meters depth and a central vertical array of 4- component receivers. This specific test acquisition set-up was and is being used both for the recording of high-quality active time-lapse seismic data as well as for continuous passive seismic data recording. The latter gave rise to the identification of a large number of surface noise related events and some very weak events possibly originating from the deeper subsurface. The active seismic data acquisition consisted of a conventional repeat survey after 2 years using an accelerated weight drop source, as well as a test with a prototype semi-permanent source located at the site during a period of 3 weeks in which CO2 injection was stopped. In both cases subtle changes at the reservoir level have been observed, though the limitations of the experimental lay-out make it difficult to come up with firm conclusions in terms of CO2 induced pressure and saturation changes. Further analysis of the data is ongoing work.Geoscience & EngineeringCivil Engineering and Geoscience