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CO2 Storage Potential of the Neogene Stratigraphy in the North Viking Graben


The Carbon Capture and Storage (CCS) industry will need to grow by at least two orders of

magnitude if it is to become a viable option for mitigating CO2 emissions. The Utsira Formation

in the Northern North Sea was selected for a pioneer project of carbon storage at the Sleipner

Field; mainly due to the high CO2 content of the produced gas, but also due to the Utsira’s large

pore volume and adequate subsurface distribution 800-1200 mbsf. Beyond the vicinity of

Sleipner however, the reservoir and seal properties are relatively unknown. Therefore, a

detailed assessment of the Utsira and its surrounding stratigraphy is required to evaluate

whether these formations could contribute to the necessary upscaling of the CCS industry.

The Utsira Formation forms part of a larger Neogene aged deltaic sequence which prograded

from the East Shetland Platform into the Viking Graben. Sleipner is situated in a sandy

depocentre in the Southern Viking Graben (SVG). For this study, complete 3D seismic

coverage calibrated with over 100 wells has been used to analyse the CO2 storage potential of

the Neogene deltaic sequence above the North Viking Graben (NVG).

A thick sandy depocentre was identified comparable in size to the Sleipner depocentre in the

SVG, however in the NVG the top depth is at 400-500 mbsf, shallower than the required 700

mbsf for safe storage. To the West the sandy Utsira units onlap the top Oligocene unconformity,

but to the East the relationship is poorly understood due to poor seismic coverage and the

reworking of sediment. Spectral decomposition, frequency blending and stratal slicing clearly

shows the sandy vs muddy facies extents, allowing confident mapping in areas of poor well

control. Sandstones are intercalated with intra-formational shale horizons with thicknesses up

to 15m and lateral extents of tens of kilometres, which would disrupt CO2 migration. Utilising

both physical and chemical trapping, gigaton volumes of CO2 could potentially be stored in the

deltaic sequence. The main risk is leakage through seal bypass systems due to reworking of

sediments and the intense glacial history. Seismically imaged potential leakage features have

been identified, mapped and flagged as hazards. Completing a full assessment of the Neogene

stratigraphy is critical for future storage site selection. From this initial screening, the results

indicate that although less than the SVG, there is still gigaton CO2 storage potential in the

Neogene sediments of the NVG.