Innovative reflection seismic acquisition for CCS applications at a transition zone in Havnsø area – Denmark

A major onshore reflection seismic survey with a total profiles’ length of approximately 130 km, was performed in 2022 in the Havnso area, in NW Zealand, Denmark. The target of the survey was to image the Havnsø domal structure and the target Gassum Formation to assess its suitability as carbon capture and storage reservoir. During the survey, eight 2D profiles were acquired using a large-offset 10-m-spaced nodal array and a short-offset 2-m-spaced landstreamer. The presence of a 3-km-wide marine channel between Zealand and Nekselø required an innovative acquisition set-up for this transition zone environment, including the onshore recorders plus a 600-m-long marine streamer and eighteen ocean bottom seismometers. Two-12-t vibrators were used as seismic source. Records from the onshore area show a good continuity of the reflections at high resolution from the near surface down to approximately 4 km depth. The transition zone acquisition improved the image of the marine channel subsurface extending the northern flank of the structure beyond Nekselo island when compared with the existing seismic data. Limitations and possible improvements on the transition zone acquisition setup are analysed for future applications. The study provides an example and a guide for future land and near-shore seismic CCS acquisitions.