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Abstract

In June 2008, a continuous injection of CO2 into the subsurface of Ketzin (approx. 25 km West of Berlin, Germany) was commenced for research purposes. By May 20112 A total of 61,396 t CO2 had been injected into the deep underground in a sandstone aquifer without any safety-related disturbances and abiding by the Federal Mining Law regulations. The initial project layout using 1 injection well and 2 observation wells was further developed in 2011 by drilling a shallow well for monitoring in the upper groundwater horizon and in 2012 by drilling another observation well for additional monitoring and the extraction of CO2 flooded samples from the reservoir. The monitoring concept developed consisted of continuous measurements of surface and underground pressure and temperature (P/T), wellbore logging campaigns including reservoir saturation and wellbore integrity measurements, gas-, hydro-, and geochemical sampling, as well as differently scaled geoelectric and seismic measurements. Besides its scientific benefits, the monitoring concept provided all the data needed for a safe and reliable operation. Furthermore, the data provided important insights into the reservoir behaviour, which can be transferred to other locations. Compared to the operational engineering of underground storage of natural gas, which has been an established secure technology for decades, differences were found in the detection of the gas distribution and the installation design of the P/T tools. The long-term experiences in natural gas storage of the operator VGS and the subcontractors UGS and ESK turned out to be essential for the effective and secure integration of best practise operational reservoir monitoring at the CO2 storage pilot site Ketzin. Based on this the next step should be to transfer the experiences gained within the scope of this project to an industrial scale, on-shore CO2 storage project as soon as possible.