현무암의 덮개암 역할 가능성에 대한 지구화학 모델링 연구

초록

This study was to evaluate whether the basalt rock can serve as a caprock overlying a storage formation. For this study, geochemical modeling was applied to simulate CO2-basalt-water interactions at various CO2 partial pressures (10, 50, and 100 bar). The results showed that the pH was changed in four stages with time, and the formation of secondary minerals was controlled by the pH of the solutions. In the first stage (pH<8.8), Ca-Mg-Fe carbonate (dolomite, siderite, and ankerite) and clay (beidellite-Mg, saponite-Mg-Mg, saponite-Mg-Na, and beidellite-Na) were newly formed. In the second stage (pH=8.8), calcite and clay minerals (chlorite-Mg and chlorite-Fe) were formed and steadily increased, and zeolite (analcime) started to precipitate. In the third stage (8.8<pH<9.7), zeolite sharply increased, while calcite and clay minerals were nearly constant. In the last stage (pH=9.7), zeolite and clay minerals consistently increased, but calcite was constant. The precipitation of the secondary minerals decreased the porosity of the basalt rock by approximately 5.4% at 10 bar, 7.9% at 50 bar, and 10.1% at 100 bar CO2. The changes in the volume of the secondary minerals showed that the formation of clay minerals played a major role in reducing the porosity in all pH ranges. This result suggests that the basalt rock can act as a caprock as the porosity of the basalt rock decreased by CO2-basalt-water interactions.

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