Abstract
AbstractUpscaling Carbon Capture and Storage requires identification of suitable storage sites, with robust reservoir seals. The Utsira Formation in the northern North Sea has been flagged as a target for further storage. However, there are no regional studies of seal variability addressing heterogeneities that could facilitate seal bypass. This study aims to: (a) identify, assess and map the elements that promote or restrict fluid migration, (b) develop a matrix to regionally map containment confidence (CC) and (c) rank the different areas for CO2 containment across the Utsira Formation. The seal and overburden were mapped using a high‐resolution, pre‐stack depth‐migrated 3D broadband seismic reflection dataset and 141 exploration wells. Seal geometry, sandstone presence and sandstone connectivity in the seal and overburden were assigned relative CC scores, which were summed to map overall CC of the Utsira Fm. Indicators for shallow gas and migration were mapped and correlated with the other elements. Areas with the lowest CC are in the west of the Utsira Fm. Here, sandstones within the Seal Interval are connected through the overburden via sandy submarine fans. In the southeast, dipping stratigraphy downlaps onto the Utsira Fm., increasing the potential for connection with glacially‐derived channel‐lobe systems in the overburden. The areas with the highest CC are the central and northeast parts of the Utsira Fm., where the Seal Interval is mudstone‐dominated and parallel to the reservoir, and channel‐lobe systems identified in the Overburden Interval are disconnected from the reservoir. This area coincides with a thick depocentre of the northern Utsira Fm. These results can be used to inform CO2 storage site selection and constrain future CO2 plume simulation analyses for the Utsira Fm. The CC matrix outlined here can also be adapted and applied to regionally assess the containment of other potential CO2 storage reservoirs in any setting.
Highlights
Large-scale Carbon Capture and Storage (CCS) projects will be critical for developing the low carbon solutions required to reduce net CO2 emissions (IEA, 2016, 2017; Stocker, 2014)
This study has shown that CC of the seal and overburden is not uniform across the northern Utsira Fm. as a result of potential fluid migration pathways, and this must be considered in future CO2 storage site selection
The Utsira Fm. in the northern North Sea is a potentially promising reservoir target for upscaled CO2 storage, but a minimum requirement is that CO2 can be contained via a low permeability, laterally extensive seal
Summary
Large-scale Carbon Capture and Storage (CCS) projects will be critical for developing the low carbon solutions required to reduce net CO2 emissions (IEA, 2016, 2017; Stocker, 2014). The North Sea subsurface contains over two thirds of the CO2 storage capacity of northwest Europe (Höller & Viebahn, 2011) It is a prolific hydrocarbon region, proving that fluid can be stored in its formations for millions of years. The southern region of the Utsira Formation (Fm.) contains the Sleipner CO2 injection site, which has been operational since 1996 and is one of only four dedicated CO2 storage projects injecting into saline aquifers (Chadwick et al, 2004; Ringrose & Meckle, 2019) (Figure 1a). Having a robust regional understanding of the seal is important for risk assessment and mitigation, as reservoir fluid could migrate within the reservoir to less favourable sealing areas
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