Long-term effects of CO2 leakage on geochemical composition of groundwater in aquifers composed of various geological media

Abstract:

CO₂ capture and storage (CCS) is one of the prospective CO₂ reduction technologies; however, leakage from the underground reservoir can lead to changes of the groundwater environments. This study systematically evaluated the changes in groundwater composition due to leakage of CO₂ in various geological media through column experiments, which were operated for about 1 year. Four columns were set up and filled with the soil from the Environmental Impact evaluation Test (EIT) facility of the Korea CO­₂ Storage Environmental Management (K-COSEM) research center, clean sand, sand and limestone mixture, and Quaternary alluvium sediment from a coastal area of Korea, respectively. The synthetic groundwater simulating the EIT site groundwater, which was saturated with 100% CO₂, was used as the influent water, and the changes in geochemical composition in time and space resulting from CO₂ leakage was monitored for each column. As the aquifer materials were reacted with CO₂, generally pH decreased and electrical conductivity (EC), alkalinity, and cation concentrations were increased. However, the patterns of the changes in geochemical composition varied depending on the characteristics of the geological media. For example, in the EIT and sand columns, the concentrations of Si were particularly high increasing up to 20 mg/L, and Cr and As concentrations were detected higher than the other columns. In the limestone column, Ca and alkalinity concentrations were very high; the dissolution of CaCO₃ resulted in Ca concentration close to 300 mg/L. On the other hand, Quaternary alluvium column showed high concentrations of Mg and Na due to the characteristics of marine alluvial soils, and also showed the rapid change of the geochemical parameters at the beginning of the experiment. These differences may be attributed to the pH buffer capacities of different geologic media. The trends in the increases in EC, alkalinity, and cation concentrations were declined over time. The results of this study can be useful in monitoring the potential CO₂ leakage in various aquifer environments and managing the impacts on groundwater geochemistry. This research was supported by the “R&D Project on Environmental Management of Geologic CO₂ Storage” from the KEITI (Project Number: 2018001810002).