Solving the carbon-dioxide buoyancy challenge: The design and field testing of a dissolved CO₂ injection system

Long-term security is critical to the success and public acceptance of geologic carbon storage. Much of the security risk associated with geologic carbon storage stems from CO₂ buoyancy. Gaseous and supercritical CO₂ are less dense than formation waters providing a driving force for it to escape back to the surface via fractures, or abandoned wells. This buoyancy can be eradicated by the dissolution of CO₂ into water prior to, or during its injection into the subsurface. Here we demonstrate the dissolution of CO₂ into water during its injection into basalts leading directly to its geologic solubility storage. This process was verified via the successful injection of over 175t of CO₂ dissolved in 5000t of water into porous rocks located 400-800m below the surface at the Hellisheidi, Iceland CarbFix injection site. Although larger volumes are required for CO₂ storage via this method, because the dissolved CO₂ is no longer buoyant, the storage formation does not have to be as deep as for supercritical CO₂ and the cap rock integrity is less important. This increases the potential storage resource substantially compared to the current estimated storage potential of supercritical CO₂.