f Could CO2 Storage Site Performance Be Compromised by Palaeo-Gas Migration Conduits in the Overburden?

Formations below the North Sea are proposed as a major repository for anthropogenic CO2 to mitigate climate change. Two such sites are already operational offshore Norway. Large areas of the North Sea are known to have leaked natural gas over geological time, so are these areas suitable for CO2 storage, given that geological heterogeneities and natural gas palaeo-migration pathways could serve to compromise CO2 storage sites in the longer term? We have identified similar features at the Utsira CO2 storage site offshore Norway, thus we use this site as a case study to investigate whether CO2 leakage is possible and if so under what conditions. We evaluate the main uncertainties affecting this storage site and present a risking methodology and screening tool that could be used to assess future storage sites and minimise the risk of compromise due to inappropriate site location.