Abstract

Interpretation and depth conversion of an extensive, well-calibrated seismic database provide the basis upon which to map the limits and evaluate the geologic risks of using a saline aquifer target for carbon dioxide (CO2) storage in the Moray Firth Basin of the North Sea. The seismic interpretation demonstrates that the Lower Cretaceous (Albian-Aptian) Captain Sandstone Member is a continuous, interconnected reservoir that rises to subcrop in the western areas of the basin as a consequence of Early Cenozoic uplift and tilt. As such, the aquifer forms an open system with few barriers or sizable closures to arrest or entrap light fluids and gases en route to its western subcrop. The new interpretation also indicates that the saline aquifer is cut by several west-southwest/east-northeast-striking reactivated normal faults. Although migration along the faults permitted hydrocarbons to get into structurally elevated traps, such as the Captain Field itself, some faults also breach the seal of the Captain Sandstone Member aquifer, rise to the seabed, and increase the risk of seabed leakage. Consequently, despite its large storage capacity, the dip, subcrop, and fault reactivation affecting the Captain Sandstone Member aquifer all suggest that its use as a site for CO2 storage remains unproven and is not the best choice for an initial North Sea exemplar. As such, the study highlights the importance of undertaking a robust and forensic geologic screening of any prospective storage site prior to injection.

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