The role of supercritical carbon dioxide in modifying the phase and interfacial properties of multiphase systems relevant to combined EOR-CCS

Deep knowledge of interfacial properties and phase behavior is decisive for designing processes of oil recovery and carbon storage. The current study aims at investigating the impact of CO2 on relevant properties in binary and ternary model systems. Experimental density data of aqueous and hydrocarbon phases along with their CO2-saturated solutions are reported at pressures up to 250 bar, representing a feasible range of CO2 utilization in EOR and CCS. The interfacial tension (IFT) is determined in binary CO2-oil systems and ternary CO2-water/brine-oil systems as a function of pressure at 60 °C using the Axisymmetric Drop Shape Analysis (ADSA) technique. It is confirmed that IFT is a decreasing function of pressure in both systems. In ternary systems, CO2 acts as an amphiphilic molecule between the coexisting immiscible phases, reducing IFT as the pressure is increased. The impact of salt concentration on the IFT in ternary systems has also been investigated. The IFT is found to acquire its highest value at high salt concentrations. Additionally, a method for quantifying the real volumetric expansion (swelling) of the oil is proposed, and a systematic investigation of volumetric expansion as a function of pressure and aqueous phase composition is performed. It is shown that the swelling increases with pressure and decreases with salinity. Our findings confirm that the solubility of CO2 in the aqueous phase impacts both IFT and volumetric expansion. Lastly, a new approach to infer CO2 solubility in the oleic phase, based on volumetric expansion and density data, is developed and presented.