An experimental study of dolomite dissolution kinetics at conditions relevant to CO2 geological storage

The kinetics of dolomite dissolution have been experimentally investigated under subsurface conditions characteristic of the Rotliegend gas fields in the NE of The Netherlands. Experiments were performed in closed, stirred, batch reactors at far from equilibrium conditions, with dolomite powders of different grain sizes. The experiments were repeated for all grain sizes at 25 degrees C and an experiment was also conducted in deionized water. The rates were derived from the measured concentrations of Mg2+ or Ca2+ released from dolomite dissolution and were normalized by the surface area of the minerals at each time interval. Regression of the rates with the pH resulted in the kinetic rate constants of: log k(1) = -8.16 +/- 0.06 at 25 degrees C and log k(2) = -7.61 +/- 0.05 at 100 degrees C (300 - 350 mu m), log k(3) = -7.88 +/- 0.20 at 25 degrees C, log k(4) = -7.45 at 100 degrees C (75 - 100 mu m), log k(5) = -6.62 +/- 0.50 at 25 degrees C and log k(6) = -5.96 +/- 1 at 100 degrees C (20 - 25 mu m). The results obtained in this study indicate that in an acidic regime the dissolution of dolomite in brine is a factor of 2 faster than in deionized water. It was also shown that the dissolution rates, when normalized by surface area, increase with decreasing grain size.