Will dawsonite form during CO 2 storage

For more than a decade, a debate has been going on as to whether dawsonite can sequester CO 2 , and be the dominant secondary carbonate where reservoirs lack divalent metal cations. Numerical simulations have suggested large‐scale formation, whereas natural occurrences in present‐day or previously CO 2 ‐charged reservoirs are scarce. Natural occurrences, such as in sequences of the Hailaer and Songliao basins, may nevertheless suggest that dawsonite can form under CO 2 storage conditions (>120 °C) given the right temperature‐composition window. The exact conditions, however (CO 2 pressure, alkalinity, temperature, ionic strength) are highly uncertain. Moreover, there are no data on the rate of nucleation and growth of dawsonite, and numerical predictions are forced into using simplified kinetic expressions with values of kinetic constants obtained from far‐from‐equilibrium dissolution rate experiments, a method that is questioned today. There are good indications that a range of reservoirs may become supersaturated with respect to dawsonite during CO 2 storage, but this does not imply spontaneous growth. The retention time (the nucleation stage) may be long, and growth rates may be significantly lower than predicted from the far‐from‐equilibrium dissolution rates. The lack of nucleation and growth rate data for dawsonite, the lack of dawsonite growth in laboratory experiments under CO 2 storage conditions (not highly alkaline), and the uncertainty in growth conditions for the natural analogues, thus render numerical predictions highly uncertain. Conclusions on the mineral carbonatization potential should therefore be taken with caution if dawsonite is the dominant secondary carbonate predicted to form. © 2013 Society of Chemical Industry and John Wiley & Sons, Ltd