Experimental investigation for the impact of chlorite dissolution on CO2 mineral trapping in a sandstone-brine-CO2 system

The mineral trapping of CO2 in geological formation is the most promising and safe mechanism for permanent carbon storage. The chlorite shows a great influence on the form and capacity of carbon storage in sandstone reservoirs due to its wide distribution and strong chemical activity. In this paper, to better understand the dissolution process of chlorite after the injection of CO2 and its potential impacts on carbon mineral trapping patterns, two sets of hydrothermal batch reactions toward chlorite and CO2 fluid are conducted at elevated temperature-pressure conditions (120 degrees C/180 degrees C, 18 MPa), considering the effects of extra calcite addition and the initial concentration of Ca2+ in solution. During reactions, the changes in water chemistry and mineral surface morphology are monitored through effluent sampling and scanning electron microscope (SEM) observation, respectively and they are further analyzed in PHREEQC by the method of mineral saturation index. It is found that the simultaneous dissolution of chlorite and calcite in CO2 saturated solutions will lead to a competition for H+, and the formation of massive surface complex CaHCO3- by Ca2+ in the initial solutions will lead to the consumption of H+. These inhibit the proton-promoted dissolution of chlorite. But when the concentration of Ca2+ is increased to meet the requirements for ankerite precipitation, the demand of ankerite precipitation for elements Fe and Mg will conversely promote the chlorite dissolution. Besides, the concentration of Ca2+ required for the precipitation of ankerite is relatively low, which implies that the injected CO2 can be mineralized and trapped by the chlorite dissolution process easily. (c) 2022 Society of Chemical Industry and John Wiley & Sons, Ltd.