The geological potential of in-situ CO2 mineral storage within onshore UK formations

Carbon capture and storage (CCS) is essential for meeting the UK’s legally binding net-zero targets by 2050. In-situ mineralisaton of CO₂ in mafic rock has been established as a rapid, secure, and affordable method of geological CO₂ storage by the Carbfix projects in Iceland.

In this study, we use geochemical, stratigraphic, and volumetric analyses to assess the suitability of UK onshore mafic and ultramafic formations for in-situ mineral storage of CO₂. We find that the total Mg²⁺, Ca²⁺, Fe_tot. oxide content of some UK formations is comparable to the geological reservoirs utilised by Carbfix in Iceland. We determine the volumes of the studied formations using a combination of boreholes, digitised cross sections and GIS calculated surface areas. We find that there are significant volumes of reactive rock available for CO₂ mineral storage in the UK.

Using a method developed by Callow et al. (2018) we determine the reactive surface area within connected pore volumes in the most suitable formations for in-situ CO₂ mineral storage. Our results indicate that onshore UK formations have the theoretical potential to store multiple gigatonnes (Gt) of CO₂. This is equivalent to the storage of decades’ worth of annual UK industrial CO₂ emissions. 

Our findings highlight that in the Antrim Lava Group alone, there is between 1.6 and 21.9 million km² of reactive surface area available for CO₂ mineral storage. This equates to a potential theoretical CO₂ storage capacity of between 8 and 110 GtCO₂. These results demonstrate that the theoretical CO₂ mineral storage capacity of onshore mafic and ultramafic rocks in the UK far exceeds the CO₂ storage requirement for the UK to achieve net-zero GHG emissions by 2050. Future research efforts should prioritise the investigation of connected porosity, reactive surface area, impact by alteration and mineralisation rates specific to the formations identified by this study.