Abstract

Lab scale experiments to investigate the dissolution reaction among supercritical CO₂-sandstone-groundwater by using sandstones from Gyeongsang basin were performed. High pressurized cell system (100 bar and 50^oC) was designed to create supercritical CO₂ in the cell, simulating the sub-surface CO₂ storage site. The first-order dissolution coefficient (kd) of the sandstone was calculated by measuring the change of the weight of thin section or the concentration of ions dissolved in groundwater at the reaction time intervals. For 30 days of the supercritical CO₂-sandstone-groundwater reaction, physical properties of sandstone cores in Gyeongsang basin were measured to investigate the effect of supercritical CO₂ on the sandstone. The weight change of sandstone cores was also measured to calculate the dissolution coefficient and the dissolution time of 1 g per unit area (1 cm²) of each sandstone was quantitatively predicted. For the experiment using thin sections, mass of Ca²⁺ and Na⁺ dissolved in groundwater increased, suggesting that plagioclase and calcite of the sandstone would be significantly dissolved when it contacts with supercritical CO₂ and groundwater at CO₂ sequestration sites. 0.66% of the original thin section mass for the sandstone were dissolved after 30 days reaction. The average porosity for C sandstones was 8.183% and it increased to 8.789% after 30 days of the reaction. The average dry density, seismic velocity, and 1-D compression strength of sandstones decreased and these results were dependent on the porosity increase by the dissolution during the reaction. By using the first-order dissolution coefficient, the average time to dissolve 1 g of Band C sandstones per unit area (1 cm²) was calculated as 1,532 years and 329 years, respectively. From results, it was investigated that the physical property change of sandstones at Gyeongsang basin would rapidly occur when the supercritical CO₂ was injected into CO₂ sequestration sites.

Keywords CO₂ sequestration, supercritical CO₂, Gyeongsang basin, geochemical reaction, sandstone dissolution