CO₂ subsurface mineral storage by its co-injection with recirculating water

Carbon capture and storage (CCS) has the potential to help nations meet their Paris Agreement CO₂ reduction commitments^1,2. The ability to capture CO₂ within mafic and ultramafic rocks through mineralization of carbon is an example of such a CCS technology^3,4, but large-scale deployment has yet to be achieved^5,6. Each geologic environment in the Earth's crust requires a distinct carbon storage solution. Whereas some regions of the subsurface contain saline aquifers and sedimentary traps suitable for traditional carbon storage through the injection of high-pressure, dense CO₂ below impermeable caprocks, other regions may lack caprocks^5-9. In these regions, carbon storage is possible through the mineralization of injected water-dissolved CO₂ forming stable carbonate minerals through its reactions with reactive silicate rocks and minerals^6,10,11. A notable challenge to applying this process at scale is that it can require 20-50 times or more water than the mass of CO₂ stored¹². Here we report on an industrial-scale pilot project designed to find a carbon disposal solution for western Saudi Arabia. This arid region has large point-source CO₂ emitters, including petroleum refining and desalination facilities, but lacks saline aquifers and sedimentary traps^13-17. We find that a CO₂ injection approach based on the recirculation of subsurface fluids can eliminate the need for external water. Our results demonstrate the feasibility of carbon mineral storage in regions in which access to water resources may be limited.