Abstract

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°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 k1 = −8.16 ± 0.06 at 25°C and log k2 = −7.61 ± 0.05 at 100°C (300 – 350 μm), log k3 = −7.88 ± 0.20 at 25°C, log k4 = −7.45 at 100°C (75 – 100 μm), log k5 = −6.62 ± 0.50 at 25°C and log k6 = −5.96 ± 1 at 100°C (20 – 25 μm).

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.

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