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

Abstract

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.