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

Abstract

The mineral trapping of CO 2 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 CO 2 and its potential impacts on carbon mineral trapping patterns, two sets of hydrothermal batch reactions toward chlorite and CO 2 fluid are conducted at elevated temperature-pressure conditions (120 °C/180 °C, 18 MPa), considering the effects of extra calcite addition and the initial concentration of Ca 2+ 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 CO 2 saturated solutions will lead to a competition for H + , and the formation of massive surface complex CaHCO 3 by Ca 2+ in the initial solutions will lead to the consumption of H + . These inhibit the proton-promoted dissolution of chlorite. But when the concentration of Ca 2+ 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 Ca 2+ required for the precipitation of ankerite is relatively low,