Reservoir characterization and sedimentological interpretations at the Aurora CO2 storage site: seismic facies analysis and clinoform decompaction

Assessment of depositional environments and variations in reservoir properties play an important role within CO2 storage sites, as even small-scale heterogeneities have a significant impact on the subsurface behavior of CO2. The proposed Aurora CO2 storage site is located on the Horda Platform, in the northern North Sea. The Lower Jurassic Dunlin Group forms the storage complex, and the primary and secondary storage units comprise the saline aquifers of the Johansen Formation and the Cook Formation, respectively. Analysis supports the Lower Drake Formation as an extensive, relatively homogeneous primary sealing unit. Injection of CO2 is planned into the Johansen Formation sandstones. The formation developed as a westward prograding delta with delta-scale subaqueous sand-prone clinoforms building into shallow-marine waters, which could potentially baffle CO2 migration. Seismic facies analysis and clinoform decompaction were tested as methods for reservoir characterization. To determine the possible influence of lateral variations of the sedimentary environments and sediment partitioning within the primary and secondary storage reservoir, seismic facies analysis was performed utilizing the GN10M1 3D seismic survey and well data. Thereafter, clinoform geometries were analyzed and decompacted to enhance the prediction of lithological distributions, seismic facies, and reservoir properties of the prograding clinoforms. Clinoform geometries and heterogeneities observed within the Aurora storage site create baffles and contribute to plume dispersion, that may result in increased secondary trapping mechanisms which have a positive impact on CO2 storage. This study shows that seismic data resolution is a limiting factor for seismic facies- and clinoform decompaction analysis. Considering the poor well-control in the south, it is advised that precautions should be taken to avoid rapid pressure buildup caused by extensive baffles. Preformed seismic facies analysis in this study show laterally changing depositional environments within the Johansen Formation, where the injection area comprises a heterogeneous sediment composition influenced by a fluctuating tidal energy environment, sediment redistribution and washover processes in relation to an observed NW-SE prograding spit bar. In contrast, the northern area comprises a coarse-grained sand-rich homogeneous sediment composition, inferring a change in depositional processes to a high-energy, shallow-marine environment. The steepest dipping clinoform systems are observed in the northern study area, from which this study infers that the area is affected by lower sedimentation rates