STUDY FOR THE GEOCHEMICAL WEATHERING OF SANDSTONE IN GYEONGSANG BASIN ON CO2 SEQUESTRATION CONDITION

Lab scale experiments were performed to investigate the geochemical weathering process of sandstone by the injection of supercritical CO2 into formations of Gyeongsang basin, Korea. Two different types of sandstone slabs were manufactured for experiments (1 cm x 1 cm x 0.3 cm size for SPM analysis and 2 cm x 2 cm x 0.3 cm size for SEM/EDS and EPMA analysis). Supercritical CO2 sequestration condition (100 bar and 50 °C) was reproduced by using the high pressurized cell system. To investigate the weathering process, the surface roughness change of sandstone, caused by the supercritical CO2-sandstone-groundwater reaction was analyzed on SPM. At a certain reaction time interval, concentrations of ions dissolved in groundwater were also analyzed by ICP-OES. SEM/EDS and EPMA analysis were performed after 60 days of the reaction to identify the secondary precipitates and the change of mineral composition. The average SRV (surface roughness value) of Ca-feldspar on the sandstone slab increased from 0.168 nm to 0.924 nm for 60 days of the reaction, suggesting that the weathering of Ca-feldspar occurred in active when Ca-feldspar contacts supercritical CO2 and groundwater on the sequestration condition. Concentration of Ca2+of groundwater increased and the calcite perforations of the sandstone slab occurred for 60 days of the reaction, suggesting that the calcite in sandstones would be significantly dissolved in a short reaction time. 6.58 % of the original mass for the sandstone slab was dissolved after 60 days of the reaction. The secondary precipitate such as Ca-rich silicate mineral was observed by using SEM/EDS analysis. Results suggested that these weathering processes may change the properties of sandstone, which controls the storage capability and the distribution of CO2 injected in pore spaces.