Experimental evaluation of CO2 mineral trapping in Albian glauconite-bearing sandstone, Mangyshlak Basin, Kazakhstan.

Glauconite-bearing sandstone reservoirs represent promising targets for potential subsurface CO2 storage via mineral trapping. Nevertheless, previous studies commonly indicate that substantial CO2 sequestration through glauconite carbonation occurs on a geological timescale. In this study, we present results of a controlled experimental assessment of CO2 mineral trapping in Albian glauconite-bearing sandstones from the Mangyshlak Basin (southwestern Kazakhstan). The studied unit, composed of very fine to fine-grained sandstones, is commonly 30-40 m thick and extends hundreds of kilometers laterally. A 30-day CO2 injection batch experiment was performed at 100°C and 150 bar using a brine/rock ratio of 20. The aqueous phase exhibited a sustained increase in Fe, Na, K, Mg, and Si ions, followed by a modest late-stage decline in Mg, Fe, and Si ions, implying mineral dissolution followed by ion consumption through formation of secondary minerals. These results are supported by petrographic comparison of pre- and post-experiment mineral assemblages, which confirm the dissolution of glauconite clasts, feldspars, albite, and K-feldspar overgrowths, with minor precipitation of ankerite. Although the experiments clearly demonstrate significant dissolution of glauconite, the precise mechanisms governing the partitioning and incorporation of Fe and Mg into newly formed carbonate and/or secondary phyllosilicate phases require further mineralogical and geochemical investigations. The current results demonstrate that nascent laboratory scale glauconite carbonation can be feasible under high temperature-pressure conditions and significant concentration of Fe2+.