CO2 Storage Potential of the Neogene Stratigraphy in the North Viking Graben
Abstract
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.
AAPG Datapages/Search and Discovery Article #90350 © 2019 AAPG Annual Convention and Exhibition, San Antonio, Texas, May 19-22, 2019