Fractured basalts as reservoirs for permanent CO2 storage on the Faroe Islands

During the last decade, the pilot CarbFix project in the Iceland rift zone has provided highly promising results for permanently storing CO₂ as carbonates in basalts. A key question is whether this method can be applied in other basaltic formations worldwide where the rocks are older, the porosities are lower, the chemical compositions are different, and/or the temperatures are lower. Storing CO₂ in the subsurface necessitates injectivity, where two essential properties are permeability and porosity. In basaltic formations, porous volumes are typically found as vesicle zones, near lava flow boundaries and in flow tops, or fractures. Currently, it appears that the permeability necessary for injecting fluids in basalts is dominated by fractures. The Faroe Islands, in the North Atlantic, consist of layered basalts of Paleogene age. The aim of this study is to examine the potential of the Faroe Island Basalt Group (FIBG) as a CO₂ reservoir. To evaluate the reservoir properties of the FIBG we interpret and integrate new and existing data at multiple scales, including satellite images, UAV photogrammetric surveys, and field mapping. We have determined the distribution of large-scale lineaments (faults and dykes), flow-scale fractures, and the interaction between them in three dimensions. Here, we focus on the Malinstindur Formation, a compound basalt sequence, which is a potential pilot injection sequence because of its permeability potential. Large-scale mapping of the FIBG volcanostratigraphy is used to map the depth of the Malinstindur Formation and to determine the presence of large strike-slip faults across the archipelago. In addition, large-scale structural lineaments exhibiting a preferred EW-trending orientation are mapped. In addition, fracture analyses on different scales (from islands to outcrops), have been conducted to investigate how lava flow architectures, regional stress, and faults control fracture distribution and connectivity. The results of these analyses show that (1) the fracture density decreases with flow thickness, (2) the orientation of the internal fractures follows the same as those of the sets of regional scale lineaments, and (3) there is no link between the fracture intensity in the basalts and the distance to the regional scale lineaments. This study will serve as a foundation for determining the subsurface distribution of the Malinstindur Formation and the fracture distribution and connectivity at potential injection sites in order to estimate the potential for permanent CO₂ storage within the Faroe Islands.