3D baseline seismics at Ketzin, Germany: The CO2SINK project

Abstract A 3D 25-fold seismic survey with a bin size of 12 by 12m and about 12km2 of subsurface coverage was acquired in 2005 near a former natural gas storage site west of Berlin, as part of the five-year EU funded CO2SINK project. Main objectives of the seismic survey were to verify earlier geologic interpretations of structure based on vintage 2D seismic and borehole data and to map, if possible, the reservoir pathways in which the CO2 will be injected at 650m depth, as well as providing a baseline for future seismic surveys and planning of drilling operations. The uppermost 1000m are well imaged and show an anticlinal structure with an east-west striking central graben on its top that extendsdown to the target horizon. About 30m of throwis seen on the bounding faults. No faults are imaged near the planned drill sites. Remnant gas, cushion and residual gas, is present near the top of the anticline in the depth interval of about 250–400m and has a clear seismic signature; both higher amplitudes in the reservoir horizons and velocity pulldown are observed. Amplitude mapping of these remnant gas horizons shows that they do not extend as far south as the injection site, which is located on the southern flank of the anticline. Amplitude anomalies, gas chimneys along an east-west striking fault, show that the stored or remnant gas either has been or is presently migrating out of the reservoir formations. Summed amplitude mapping of the planned injection horizon indicates that this lithologically heterogeneous formation may be more porous at the injection site.