Geophysical Evidence for Fluid Migration and Escape in the Central Baltic Sea

• Applicant: Professor Dr. Christian Hübscher
• Subject Area: Geophysics ; Geology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 555741530

The FluidEscape project aims at the large-scale mapping of fluid seepage sites on the seabed of the central Baltic Sea in the Gotland Depression area, which have been described locally and in preliminary studies. The main hypothesis to test is: In the central Baltic Sea, fluids migrate along permeable layers in the Paleozoic basement and flow vertically or subvertically across the seal along faults, emerging at erosional unconformities or the fault’s piercing point, and then ascend through the Quaternary cover to the seabed. The faults therefore represent a seal bypass system. Source rocks, reservoirs, and migration pathways will be identified in detail, and the integrity of stratigraphic seals and barriers will be examined. The significance of the study goes beyond the aspect of environmental pollution, as the deep subsurface of the study area is considered a potential storage rock for the injection of CO2 (Carbon Capture and Storage). To achieve the project objectives, more than 9,000 km of multichannel reflection seismic and hydroacoustic profiles, measured during five ship expeditions, are available. In the first step of the work plan, the quality of the reflection seismic data needs to be homogenized, e.g. by stronger and consistent suppression of seafloor multiples. The conversion of seismic time sections to depth will follow, after the development of spatial models of seismic velocity propagation. The velocity model building will be based on borehole information, refraction analysis, and diffraction-based velocity analysis. Thirdly, the transfer of stratigraphic information from boreholes to the seismic dataset will enable the gridding and large-scale mapping of geological information after identifying faults and unconformities. This geological framework will be published in the first synthesis phase. The calculation of special seismic attributes, so-called Direct Hydrocarbon Indicators, for all seismic profiles will then serve to identify hydrocarbon accumulations in the Paleozoic basement. The migration of hydrocarbons along permeable layers or faults will be mapped and interpreted in the context of fluid seepage sites observed in hydroacoustic data on the seabed. The publication of these results will occur in the second synthesis phase. All raw and research data will be securely archived and made publicly accessible during the course of the project.

• DFG Programme: Research Grants