Effects of feldspar and salinity on the mineral sequestration capacity of CO₂ in high-salinity aquifers

Mineral sequestration of CO₂ is considered to be the safest mechanism in the long-term storage of CO₂ in deep saline aquifers. This study aims to investigate the effect of feldspar and salinity on the mineral sequestration capacity of CO₂ in deep high-salinity brine aquifers by taking Jiangling Depression of Jianghan Basin for instance. Numerical simulation on the long-term geochemical reaction and transport was performed by taking TOUGHREACT as the simulation tool. Simulation results indicate that the effect of feldspar on the mineral trapping capacity of CO₂ does not depend on the total content of feldspar, but depends on feldspar type and relative content. With Mg-rich minerals such as chlorite or dolomite present, the mineral composition abundant in K-feldspar is less favorable for the mineral sequestration capacity of CO₂ for the reason that a large amount of illite precipitates, consuming a lot of Al³⁺ in the aqueous solution, thereby limiting the precipitation of dawsonite, especially for the high-temperature sedimentary environment. In addition, the effect of salinity on the mineral sequestration capacity of CO₂ represents two aspects: one for the longer migration distance due to the lower solubility of higher salinity and the other for CO₂ mineral trapping capacity per 1 m³ medium which is not in simple decreased with salinity, depending on K-feldspar present or not. For the mineral composition with K-feldspar present, CO₂ mineral trapping capacity decreases with salinity, while with albite instead of K-feldspar, it increases with salinity owing to more precipitation of dawsonite.