On the potential of CO2–water–rock interactions for CO2 storage using a modified kinetic model

During CO2 storage, mineral trapping is the safest long-term storage mechanism, and it is therefore important to estimate the correct CO2 portion trapped in secondary mineral phases. The storage potential for cold, quartz-rich reservoirs, hereafter termed Utsira-type reservoirs, were solved using the numerical code PHREEQC, using a rate model that took into account both nucleation and growth of secondary mineral phases. This represented a modification of earlier simulations where growth rates were calculated from dissolution rate data. Because growth rate and nucleation rate parameters were largely unknown for the secondary carbonates, we did a sensitivity study on the potential for carbonate growth on rate parameters.The simulations suggest that the total amount of CO2 trapped as mineral carbonates is given by the amount of glauconite, chlorite, and smectite present in the reservoir prior to injection, as they were nearly completely dissolved. The fast dissolution of the silicates provided divalent cations for the growth of ankerite and siderite. The timing of precipitation and the secondary mineral assemblage were seen to be highly sensitive to the nucleation and growth rates. Moreover, at high nucleation rates, the secondary carbonates started to precipitate at fairly low supersaturations and formed rapidly after the dissolution of the primary minerals.Finally, a comparison of earlier simulations on the Utsira-type system with the present model and natural analogues, suggests that the earlier models have largely overestimated the growth potential of carbonates such as dolomite, magnesite and dawsonite.