High-resolution 2D and 3D seismic imaging and core-log-seismic integration of seaward dipping reflectors on the Vøring volcanic rifted margin

Offshore basalt flow sequences represent potential permanent CO₂ sequestration sites along volcanic rifted margins. The International Ocean Discovery Program (IODP) Expedition 396 drilled six basement sites on the Vøring volcanic margin in 2021, recovering more than 350 m of basaltic basement cores and 15 m of granite cores. The cores have been extensively analyzed following the IODP shipboard procedures (e.g., velocity, density, porosity, and magnetic susceptibility measurements). In addition, shore-based petrographic, geochemical, CT scanning, and multi-fluid permeability and flow measurements (nitrogen, brine, liquid and gaseous CO₂) have been performed to assess reservoir properties. A standard suite of conventional wireline logs along with borehole image (acoustic and resistivity) logs were acquired in four holes. High-resolution 2D and locally 3D seismic reflection data have been acquired across all sites during three surveys (2020, 2022, and 2024) using R/V Helmer Hansen. In total, four HR3D P-Cable cubes with a total areal extent of 62 km² and c. 2700 km of HR2D data have been collected. The seismic data are interpreted using the concepts of seismic volcanostratigraphy and igneous seismic geomorphology combined with conventional horizon interpretation and core-log-seismic integration. On the Skoll High, the igneous seismic geomorphology of the Top Basalt horizon reveals two distinct domains: a pitted surface in the west, and a faulted surface in the east. Cross-cutting faults and fracture systems are well imaged in borehole data and the 3D seismic data. Borehole data show that the Inner Seaward Dipping Reflectors (SDR) were emplaced in subaerial and coastal environments, including vesicular flow tops and deposition of inter-basalt volcaniclastic sedimentary horizons. Vesicles are observed to be both open or filled with carbonates and clay minerals within different layers, however, laboratory measured matrix permeability of mini-core plugs is typically low and in the milli to micro-darcy range; brine permeability measurements are indicating even lower. Multiple scales of fracturing are identified within the cores and image logs, and Strontium residual salt analysis revealed that they have an important impact on permeability by enhancing fluid communication between flows. In conclusion, the integrated interpretation suggests that the Vøring Margin basalt sequences may have reservoir potential in fractured intervals and flow tops, but reservoir-scale injection testing linked to fracture network parameterization is required for large-scale assessment.