In this paper our interest is in the effect of minerals on the carbon dioxide concentration. The dissolution of carbon dioxide in the oleic phase depends on the mineral content and can in itself reduce the amount of oil left behind and thus increase the recovery of oil. The calculation of the concentration of carbon dioxide requires the determination of the activity coefficients of all chemical species in the aqueous phase, which thus determine the ratio of carbon dioxide dissolved in the aqueous phase and the carbon dioxide in the oleic phase. It is the purpose of the paper to provide the complete geochemical background for the modeling of carbonated water and carbon dioxide injection in a calcite. reservoir.