Ahmed S. Elshall

The validity of mineral sequestration in saline siliciclastic aquifers in sedimentary basins is assessed in this paper. Mineral sequestration is the precipitation of carbonates due to the dissolution of silicates upon the injection of CO2 in deep geological formations, while solubility trapping is the dissolution of CO2 in the formation water. Saline reservoirs in sedimentary basins seem to constitute one of the best targets for the storage due to their huge storage capacity, low importance in terms of natural resources and wide availability and in close proximity to power generation plants. Siliciclastic aquifers are predicted to have the best potential for trapping CO2, by precipitating carbonate minerals, when they contain an assemblage of basic aluminosilicate minerals such as fledspars, zeolites, illites, chlorites and smectites. Precipitation of carbonate minerals due to the dissolution of silicate are generally not observed in laboratory experiments conducted at low temperature and pressure due to the slow dissolution rates of silicates, or the absence of significant amount of divalent cations in the rock composition. However, carbonate precipitation is observed in work conducted under relatively high pressure and temperature. On the other hand, although carbonate perception is predicted by computer simulation for larger timeframes as reported in several studies, yet laboratory and geochemical modeling work suggests that the injection of supercritical CO2 in deep saline aquifers may show limited reactivity with reservoir rocks. Thus, the dominant trapping mechanisms will be more based on the dissolution of CO2 in the formation water rather than on mineral sequestration. Accordingly, this article concludes that apart from the physical conditions such as temperature and pressure, mineral sequestration in saline siliciclastic aquifers of sedimentary basins may behave differently due to differences in brine compositions and rock types, and thus the degree of mineral sequestration is case specific.