Hydrogeochemical modeling on water-rock-CO2 interactions within a CO2-injected shallow aquifer

Abstract

Multi-dimensional and multi-phase hydrogeochemical reactive transport modeling was conducted to predict the dispersion of CO2 plume after its injection into a shallow aquifer via a controlled release test within the environmental impact evaluation test facility on seepage of geologically stored CO2 (EIT) site. In addition, the model simulations aimed at observing the change of mineralogical composition occurring as a result of water-rock-CO2 interactions. Contrary to the expectation that the injected CO2 dispersed in the direction of groundwater flow, the model simulations showed that the CO2 plume was isotopically dispersed initially and then transported preferentially towards the northeastern direction of the injection well. This result can be related to the zone of a relatively higher electrical resistivity (ER) where the injection well existed and the northeastern zone where a relatively lower ER was distributed. The results of model simulations on the change of volume factions of major minerals via water-rock-CO2 interactions for the period of 1,000 years after the CO2 injection indicate that naturally-occurring K-feldspar, albite, anorthite, chlorite, kaolinite, and glauconite seemed to be continuously dissolved as a result of decreasing pH, whereas quartz and illite were observed to be predominantly precipitated. Furthermore, it is likely that the mineral trapping of the injected CO2 was mostly contributed to calcite and dolomite. However, the volume fraction of magnesite seemed not to be changed, and which indicates that it was not precipitated under the given conditions of temperature and pressure. It is expected that these results of model simulations can be applied as one of indicators to quantitatively evaluate the long-term efficiency of mineral trapping of injected CO2.