Numerical Simulation of Impacts of Mineralogical Compositions on Trapping Mechanisms and Efficiency of Carbon Dioxide Injected into Deep Saline Sandstone Aquifers

A series of numerical simulations using a multiphase hydrogeochemical reactive transport numerical model is performed to analyze density-dependent (convective) groundwater and carbon dioxide flow and hydrogeochemical reactive transport due to geologic storage of CO₂ in a deep saline sandstone aquifer and to evaluate impacts of its mineralogical compositions on trapping mechanisms and efficiency of injected CO₂. The results of the numerical simulations show that the mineralogical compositions of the sandstone aquifer have significant impacts on hydro-chemical behavior of injected CO₂ and thus its trapping mechanisms and efficiency. Injected CO₂ is accumulated as a free fluid phase beneath the cap rock (i.e., hydrodynamic trapping), then dissolved as aqueous phases such as bicarbonate and carbonate anions into groundwater (i.e., solubility trapping), and finally precipitated as carbonate minerals (i.e., mineral trapping). Mineral trapping of injected CO₂ takes places as precipitation of a primary carbonate mineral such as calcite and secondary carbonate minerals such as dawsonite, siderite, ankerite, and magnesite. The patterns of hydrogeochemical reactions significantly depend on the initial existence of chlorite in the sandstone aquifer. For mineral trapping of injected CO₂, ankerite is the most dominant mineral when chlorite is initially present, whereas dawsonite is the most dominant mineral when chlorite is initially absent in the sandstone aquifer. Mg²⁺ and Fe²⁺, which are the essential chemical components of such secondary carbonate minerals for mineral trapping of injected CO₂, are mainly supplied by dissolution of chlorite. As a result, the precipitation amount of secondary carbonate minerals and thus the efficiency of mineral trapping of injected CO₂ increase significantly as the volume fraction of chlorite increases in the sandstone aquifer. This work was supported by the Energy Efficiency and Resources Program grant (No. 2010201020001A) funded by the Korea Institute of Energy Technology Evaluation and Planning (KETEP), Ministry of Knowledge Economy, Republic of Korea.