Characterization and evaluation of two deep saline aquifers and caprock for carbon dioxide storage offshore Sweden

As part of a three-year government assignment to evaluate the potential for geological storage of carbon dioxide in Sweden, the Geological Survey of Sweden has carried out geophysical and geological investigations of deep saline aquifers and caprocks in two areas offshore southern Sweden with very different geological settings: (1) the Lower Palaeozoic succession southeastern Baltic Sea investigations have been focused on offshore the island of Gotland, and (2) the  Upper Mesozoic succession of the southwestern Baltic Sea, offshore Scania – the southernmost part of Sweden. Here we present the results from the two areas are based on two new core drillings in each area combined with onshore and offshore legacy core and seismic data, newly acquired deep seismics from onshore Gotland and Scania as well as offshore Scania. The caprocks in both areas have thicknesses exceeding several hundreds of meters, with low porosities and permeabilities, however, the potential reservoir units present two very different case studies. The Faludden Member consists of homogenous medium-grained quartz arenite with high porosity and permeability, and patchy dolomite cement, while the Arnager Greensand is heterogenous with a lower textural and compositional maturity, consisting of poorly sorted fine- to medium-grained glauconitic sandstones, with varying degrees of consolidation due to intervals of phosphorite concretions and varying content of detrital clay minerals. Despite the difference of the two reservoirs, both are considered suitable candidates for geological storage and further investigations are warranted. Implementation of national CO₂-storage sites would contribute to Sweden's goal of net zero greenhouse gas emissions in 2045 and EU's goal to be climate neutral by 2050.