Monitoring permanent CO2 storage by in situ mineral carbonation using a reactive tracer technique.

In situ mineral carbonation provides the most effective and permanent solution for geologic CO 2 storage. Basaltic rocks have the potential to store large volumes of CO 2 as (Ca, Mg, Fe) carbonates [1] . Existing monitoring and verification techniques for geologic CO 2 storage are insufficient to quantitatively characterize solubility and mineral trapping in a geologic reservoir. We developed and tested a new reactive tracer technique for quantitative monitoring and detection of dissolved and chemically transformed CO 2 . The technique involves the active tagging of the injected CO 2 with low levels of radiocarbon ( 14 C) as a reactive tracer in combination with the injection of non-reactive tracers such as sulfurhexafluoride (SF 6 ) and trifluoromethylsulphur pentafluoride (SF 5 CF 3 ). The tracer technique has been applied at the CarbFix pilot injection site in Hellisheidi, Iceland as part of a comprehensive geochemical monitoring program during two injection phases; Phase III and IV. SF 6 and SF 5 CF 3 confirm the arrival of the injected CO 2 and CO 2 +H 2 S solutions at the first observation well HN04, which is 125m west of the injection well at 520 m depth. The initial breakthrough of the migrating dissolved CO 2 front occurred 63 and 62 days after injection began as evidenced by an initial peak in the SF 6 , SF 5 CF 3 , 14 C, and dissolved inorganic carbon (DIC) concentrations. The major increase in the non-reactive tracer concentrations occurred several months after the initial breakthrough, although no major concentration increase has been observed for 14 C and DIC suggesting that mineral reactions are dominant during CO 2 injection. [ABSTRACT FROM AUTHOR]