The Baltic Basin is known for its numerous Paleozoic hydrocarbon reservoirs. There is published evidence that hydrocarbons are leaking from the seafloor, however, little is known about the hydrocarbon migration pathways from Paleozoic source and reservoir rocks toward the seafloor and their escape structures. To investigate these processes, we utilize a new set of multibeam, parametric sediment sub‐bottom profiler and 2D seismic reflection data. The integrated analysis of seismic profiles, diffraction imaging and bathymetric maps allow to identify a hydrocarbon migration system within Silurian and Devonian strata that consists of layer parallel and updip migration beneath sealing layers, migration across seals along faults, and seafloor escape structures in form of elongated depressions. The general migration trend is directed updip, from the Paleozoic reservoirs below the southeastern Baltic Sea toward the Gotland Depression in the northwest. The locations of the hydrocarbon escape structures at the seafloor and their elongated shape are mainly controlled by the regional geological setting of outcropping Paleozoic layers. In addition, iceberg scouring may have facilitated hydrocarbon migration through the Quaternary deposits. The description of this hydrocarbon migration system fills the gap between the known reservoirs and the observed hydrocarbon accumulations and seepages. With regard to potential Carbon Capture and Storage projects, the identification of this hydrocarbon migration system is of great importance, as potential storage sites may be leaking.
N2 - Plain Language Summary: The Baltic Basin including the Baltic Sea is well known for its hydrocarbon reservoirs with ongoing oil production since the 1940s. While there is some published evidence that hydrocarbons are leaking from the seafloor, little is known about the pathways from the reservoirs toward theses leakages. In this study, we use three imaging techniques for the seafloor, the uppermost sediments and the first few kilometers of the subsurface to image the hydrocarbon migration pathways and their escape structures. We find that hydrocarbons are migrating along dipped geological layers from the reservoirs in the southeast toward the Gotland Deep in the northwest. Additionally, we also observe that hydrocarbons are penetrating through these geological layers at locations of pre‐existing small‐scale fractures. The locations, at which the hydrocarbons escape from the seafloor, are mainly controlled by the regional tectonic setting. In addition, iceberg scouring may have had an influence on the exact escape locations. With our findings in this study, we fill the gap between the known reservoirs and the observed seepages and can contribute to questions regarding the potential storage of CO2 in the Baltic Basin. N2 - Key Points:Numerous elongated fluid escape depressions are observed at the eastern margin of the Gotland Deep, central Baltic Sea
First evidence for fluid migration pathways from Paleozoic toward Quaternary strata in the region
Locations of fluid escape is controlled by the regional tectonic setting