Rien Herber

Effect of Reactive Surface Area of Minerals on Mineralization Due to CO2 Injection in a Depleted Gas Reservoir

In this research, long-term (up to 1000 years) geochemical modeling of subsurface CO2 storage was carried out on Permian Rotliegend reservoirs of depleted gas fields in northeast Netherlands. The results showed that mineral dissolution/precipitation has a minor effect on reservoir porosity. In order to validate this, we focused on the reactive surface area of minerals which we measured by scanning electron microscopy. These calculations resulted a range of surface area values for each mineral which were subsequently subjected to a parameter analysis and Monte Carlo uncertainty analysis. These analyses revealed that in the Rotliegend sandstones, the surface area of quartz has by far the largest effect on SMCO2 (total amount of CO2 sequestered as mineral). Mineral trapping of CO2 increased significantly with increasing quartz surface area. This leads to the conclusion that CO2 injection in a sandstone reservoir with fine grained quartz has a higher potential for mineral trapping of CO2. In addition, using parameter analysis we also could determine the effect of surface area of each mineral on its own dissolution/precipitation mechanisms as well as on the other minerals. For example, our results showed that dawsonite precipitation is proportional to kaolinite and K-Feldspar surface area.

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°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.