Development and post-depositional deformation of a Middle Eocene deep-water sandy depositional system in the Sørvestsnaget Basin, SW Barents Sea

Abstract

Three-dimensional seismic data from the Sørvestsnaget Basin, SW Barents Sea supported by well data, are used to investigate a Middle Eocene deep-water depositional system. The system forms a NNW-oriented sediment accumulation, characterized by increased seismic amplitudes, and abrupt western termination. The data indicate that post-depositional sand remobilization and injection led to formation of sub-circular sediment blocks up to several km wide to the east of the main accumulation. The deep-water depositional system was deformed by wing-like sandstone intrusions, extending 200–400 m upwards from the margins of the parent sand bodies. The intrusions have polygonal or broadly circular plan view geometries. Deformation is inferred to have been associated with overpressure of the sand bodies as a result of rapid burial, fluid migration into the sealed sand bodies from deeper sources via synsedimentary faults, and fluid drainage from the surrounding mudrock during early compaction. The final triggering mechanism for sand remobilization and injection is inferred to have been fracture propagation due to differential compaction and/or fault-induced earthquakes. The injectite complexes are often associated with folding of overlying strata, which we relate to differential compaction. Intrusion of sand took place during the Middle Eocene. Post-depositional sand remobilization and injection have important implications for hydrocarbon exploration because they cause changes in the reservoir primary architecture, connectivity and structure.