Effects of AOT, AES on Swelling Factor and Interfacial Tension for Carbonated Water Solution, Synthetic Resinous, Asphaltenic Oil and crude oil; Subcritical and Supercritical Conditions

In recent years, the application of gas injection, particularly carbon dioxide (CO ₂ ) dissolved in water, known as carbonated water (CW), has gained increasing attention. This technique has been employed in a miscible form to activate several mechanisms, such as wettability alteration, interfacial tension (IFT) reduction, and the swelling of crude oil. Although these mechanisms can be triggered, it is possible to enhance those using surfactants in conjunction with CW. The combination can optimize IFT reduction and wettability alteration due to the presence of surfactants, while the swelling effect still originates from the CO ₂ in the solution. In this context, the current study is designed to examine the effect of CO ₂ dissolution in water under pressures ranging from 500 psi to 4500 psi, covering subcritical to supercritical conditions, and at temperatures between 25°C-65°C. Additionally, the synergistic effects of surfactants, namely dioctyl sulfosuccinate sodium salt (AOT) and sodium dodecyl polyoxyethylene ether sulfate (AES), were examined at concentrations ranging from 0 to 700 ppm, along with the dissolved CO2 on IFT and swelling factors. The measurements revealed that as the pressure increased, the swelling factor reached a maximum value of 19.3% when it was contacted with crude oil, while the maximum swelling factor for the solutions contacted with synthetic mixed resinous and asphaltenic oil (SMRAO) was reached at a value of 22.3%. The second oil type was selected as SMRAO since crude oil comprises thousands of components, making it hard to extract any generalized conclusions based on the obtained results. In this way, using only one or two specific fractions, especially resin and asphaltene which acts as natural surfactants, providing the chance to examine the generalized interactions between chemicals and oil fractions. The measurements revealed that the presence of surfactant in the carbonated water (CW) reduced the swelling factor up to 50% for AOT and 38% for AES as the pressure and temperature and surfactant concentration increases. The reason of this observed trend was correlated to the bulky structure of AOT compared with the linear chain-like structure of AES. Besides, the measurements revealed the positive impact of pressure and temperature on a higher swelling factor regardless of the used surfactants, which can be due to the higher dissolution of CO ₂ under higher pressures and better movement and migration of CO ₂ molecules, which means a penetration of higher amount of CO ₂ into the oil drop leading to higher swelling factors. In the next stage, the IFT of different solutions under different temperatures (25 ^o C-65 ^o C) and pressures (0-4500 psi) was measured. The obtained IFT values showed that using SMRAO instead of crude oil has a reducing impact on the IFT values with minimum value of 19.2 mN/m, while the IFT value for similar thermodynamic condition and crude oil was 23.1 mN/m. Besides, further IFT measurements revealed that although increasing pressure has a reducing impact on the IFT, increasing temperature increases the IFT values regardless of the presence of surfactant or even the type of surfactant. The measurements also revealed that the effect of AES on the IFT reduction was better than AOT, leading to a minimum IFT value of 1.1 mN/m for AES concentration of 700 ppm dissolved in CW with pressure and temperature of 4500 psi and 65 ^o C, respectively due to longer alkyl chain length and easier packing in the interface compared with AOT which has a bulky structure prevents the high number of AOT molecules to be packed in the interface. The measured IFT values revealed the linear IFT variation behavior for the systems were in contact with SMRAO compared with crude oil due to this fact that the SMRAO has less complexities than crude oil comprises of thousands of components makes the IFT variations more straightforward for SMRAO.