Unveiling subtle structures with attribute analysis at a potential geological carbon storage site in denmark

Characterizing near-surface fault architecture and structural framework is critical for geological carbon storage (GCS) sites, as it directly influences storage maturation, integrity, and associated risks. Building on earlier interpretations, this study revisits the Gassum domal structure, a potential GCS site in eastern Jutland, Denmark, using seismic data acquired in 2023. The main aim is to address primary risk zones and delineate structural features that were previously not delineated. We applied spectral decomposition and red-green-blue (RGB) co-rendering to migrated reflection seismic sections to improve the imaging of faults and weakness zones. Spectrally decomposed attributes were further combined with first-break traveltime tomography to derive tuning thickness, providing a first-order approximation of layer thicknesses. This approach revealed detailed and complex fault architecture, including internal faulting within the near-surface secondary seal, the Chalk Group. The highest fault densities occur at the dome crest and within the spill-point zone; two areas critical for CO₂ leakage. Our results indicate that the Gassum structure poses structural risk and must be carefully studied for its fault network integrity to ensure long-term CO₂ storage without significant de-risking.