Study of the Effect of Acid Number on the Interfacial Tension Between Carbon Dioxide and Different Combinations of Diesel Fuel and Gasoline at Different Pressures

The process of injecting carbon dioxide (CO₂) into oil reservoirs involves intricate interactions between the reservoir’s hydrocarbons and CO₂, resulting in changes to various physiochemical properties such as interfacial tension (IFT) between complex acidic hydrocarbons and CO₂. The IFT plays a crucial role in enhanced oil recovery by altering capillary force. Hydrocarbon mixtures usually contain a percentage of acidic organic compounds that pose a crucial effect on IFT measurement. In this study, benzoic acid was chosen as a representative of acidic compounds to study the effect of acid number (0.0–0.8 g/L) on the IFT between CO₂ and different combinations of diesel fuel (representing aliphatic hydrocarbons) and gasoline (representing aromatic hydrocarbons). The volume ratios of the mixtures were varied at 0:100, 25:75, 50:50, 75:25 and 100:0%. Results revealed that increasing the acid number in gasoline from 0.2 to 0.8 g/L led to a significant change of more than 10 dyne/cm in the IFT between aromatic hydrocarbons and CO₂. On the other hand, IFT alteration for aliphatic hydrocarbons was observed to be up to 5 dyne/cm. A new correlation for estimating IFT between CO₂ and different hydrocarbons was also proposed with an average relative error of less than 9%.