Reaction of drilled-cores from the Janggi basin with CO₂-saturated brine from subcritical to supercritical condition of CO₂: Implications on sequestration of dissolved CO₂

The CO₂-brine-core reaction was studied to provide information for geological CO₂ sequestration in the Janggi basin. Three drilled-core samples (two caprocks and one reservoir rock) at different depths in the basin were used for the reactions under subcritical and supercritical conditions of CO₂ (10 bar–170 bar at 40 °C). Due to the dissolution of various ions from the cores during the reactions, the ion composition and concentration were changed in the brine, causing the experimentally determined solubility of CO₂ in brine to change. Therefore, the change in the solubility of CO₂ in brine was affected by the type of core and pressure. In addition, to simulate the effect of an additive on the CO₂ solubility, alkyl-olefin sulfonate (AOS; 1 wt%), which is widely used for CO₂ enhanced oil recovery (CO₂-EOR), was added to the CO₂-brine-reservoir rock reaction system. The addition of the surfactant contributed to improving the solubility of CO₂ mainly in the high-pressure region. The change in the textural structure (mesopore and micropore) and chemical composition of core were also observed in nano-scale aspects despite the short experimental period (12 days). The introduction of AOS reduced the nano-scale structural change of the reservoir rock. The results in brine and cores can contribute to improving the understanding of CO₂-brine-core reactions, because more accurate estimation of CO₂ storage capacity after reactions can be feasible in designing and operating CO₂ sequestration.