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Abstract

Under the coordination of the German Research Centre for Geosciences GFZ the first European onshore CO2 storage project was initiated in 2004 at Ketzin, approximately 25 km west of Berlin, Germany. About 67 kt of CO2 (purity > 99.9%) were injected into a saline aquifer from June 2008 until August 2013. All project stages were accompanied by a comprehensive monitoring and modelling program, focusing on the investigation of the processes involved and to assure leakage-free CO2 injection and save geological storage. Hence, methods from different geoscientific disciplines were applied, targeting the reservoir itself, the cap rock, the above-zone and the surface (Martens et al. 2015, Wipki et al. 2016). Here we report on the results of the long-term surface monitoring with continuous soil CO2 flux measurements. A profound and extensive database of measurements performed before injection started serves to interpret data during and after CO2 injection (Zimmer et al. 2011). As the CO2 flux measurements reflect the specific site conditions, which can vary locally and over time, trends must be interpreted carefully. After an exploration phase in 2004 and drilling of the first wells in 2007, CO2 was injected between 2008 and 2013 into Upper Triassic sandstones at a depth of 630 to 650 m. This reservoir is overlain by more than 165 m of shaley cap rocks. The site itself is located at the southern flank of the Roskow-Ketzin double-anticlinal structure (Martens et al. 2014, Förster et al. 2006, Förster et al. 2009) and the stored CO2 mainly migrated in northern to western direction (Wipki et al. 2016 ). Additionally, soil profiles of 70 cm depth were studied for their structure and carbon and nitrogen concentrations. The results helped to explain the spatial variations of the soil CO2 fluxes at the different locations (Zimmer et al. 2011). However, as most of the sampling positions are located next to agricultural roads and fields, an influence of used fertilizers and arable farming on the soil structure, chemical composition and the soil biology cannot be ruled out.