Diffusion coefficient of CO2 into light hydrocarbons and interfacial tension of carbonated water-hydrocarbon system

Abstract

The interfacial tension (IFT) and diffusion coefficient of CO2 in a hydrocarbon in a carbonated water (CW) environment were estimated for pressures between 10-100 bar and at temperatures of 25 °C, 35 °C, and 45 °C using axisymmetric pendant drop shape analysis (ADSA). We developed a dynamic numerical model accounting for the changes in properties at the CW-hydrocarbon interface owing to the swelling of the hydrocarbon drop (HD). This approach eliminates an error of about 36% arising from the assumption of a static boundary/volume in conventional methods. The results indicated that the IFT between CW and the hydrocarbon is a function of the CO2 phase density and solubility. At low pressures (<60 bar, 25 °C), IFT is directly proportional to the pressure, while at pressures larger than 60 bar, it is inversely proportional to the pressure. The physical behaviour of the CW-hydrocarbon system is driven mainly by a balance between CO2 solubility and IFT, resulting in a constant CO2 saturation. Despite the decrease in CO2 solubility with temperature, the diffusion coefficient of CO2 increases. The reduction in IFT with temperature counteracts the decrease in CO2 solubility, leading to a higher diffusion coefficient as temperature increases. It is shown here that the CW-hydrocarbon system induces more swelling and lower viscosity compared to similar systems but with pure CO2. As such, CW's potential for enhanced oil recovery (EOR) is realised.