Thermodynamic and Interfacial Characterization of Petroleum Industry Surfactants: A Study on Critical Micelle Concentration and Interfacial Tension Behavior under Mild Conditions

Surfactants play a vital role in oil and gas applications, particularly in enhanced oil recovery (EOR), where interfacial tension (IFT) reduction and micellization are key to improving fluid mobility. This study aims to evaluate the interfacial and thermodynamic properties of five widely used petroleum surfactants to better understand their efficiency under mild reservoir-like conditions. IFT is measured using the spinning drop tensiometer across a temperature range of 25-40 °C, while critical micelle concentrations (CMC) are determined via conductometric methods. Thermodynamic parameters of micellization are calculated from temperature-dependent CMC data. The results show that micellization is an entropy-driven process for all tested surfactants. The studied surfactants significantly reduce IFT values within the tested temperature range, underscoring their potential for practical application in EOR formulations. The study also confirms that accurate determination of CMC is essential in optimizing surfactant efficiency under varying environmental conditions.