Difficulties encountered during the processing of the timelapse 3D land-seismic data at the CO2 geological storage site at Ketzin, Germany, were to a large extent attributed to changes in near-surface velocities. Two workflows for processing of the 4D data were tested. The first one included re-calculation of the refraction static corrections based on new information about the near-surface from first breaks. This workflow showed that the near-surface changes could only imperfectly be resolved by new refraction static corrections. The second workflow included cross-correlation of the traces acquired at the same locations but during different campaigns and calculation of the prestack time shifts between the surveys. Both workflows demonstrated their capability to minimize the time-lapse noise and enhance the time-lapse reservoir signature. They provide similar time-lapse results, except that the cross-correlation workflow is quicker, more accurate and displays less time-lapse noise.


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