CO2 Solubility in Brine Aquifers – Volumetric Considerations

Abstract

Abstract A thermodynamic model concept and model parameters are presented for predicting the solubility of CO2 in pure water and in water with one or more of the salts, NaCl, KCl, CaCl2 or MgCl2. A cubic equation of state with a non-classical mixing rule is used to describe the mutual solubility of CO2 and H2O. Classical mixing rules with a temperature-dependent binary interaction parameter are used to describe the interactions between H2O and salt ions and between CO2 and salt ions. A good agreement is seen with the experimental data for the CO2 solubility in brine. The solubility of CO2 in brine is important when assessing the possibilities for storing CO2 in saline aquifers. The presence of salt in an aqueous solution reduces the solubility of CO2 by 2.5-3% for each weight% of salt added. Very large amounts of water are required, if a considerable part of the CO2 produced by combustion of oil and gas is to be stored and dissolved in saline aquifers. For example, it takes approximately 50 m3 of water to dissolve the CO2 produced by burning 1 reservoir m3 of oil.