Characterization of the lower Palaeozoic regarding its CO2-storage potential in the Swedish sector of the Baltic Sea

Two cored boreholes were drilled in 2023 through the Cambro–Silurian succession on the southernmost part of the island of Gotland as part of a project coordinated by the Geological Survey of Sweden to assess the CO 2 -storage potential in the Cambrian sandstone reservoirs in the south Baltic Sea. The investigations were performed in cooperation with the Swedish national research infrastructure for scientific drilling “Riksriggen”. We describe and assess the drilling, geophysical wire-line logging, and stratigraphical, lithological, and petrophysical analysis of the Cambro–Silurian succession. The results are discussed with respect to the reservoir and sealing properties for CO 2 -storage. The results indicate that the Faludden sandstone, along with the overlying Ordovician and Silurian caprock interval meets the necessary requirements for CO 2 -storage. In contrast the Cambrian Viklau and När sandstone intervals display less favourable reservoir conditions due to high degree of cementation contributing to very low permeability. Formation integrity tests and laboratory analyses verify an Ordovician and Silurian caprock interval with high compressive strength and low permeability. This new information strengthens the judgement that CO 2 storage is feasible in the Swedish sector of the Baltic Sea.