Oil-Targeted Microcapsules Based on Ethyl Cellulose Containing Green Surfactant Systems with High Interfacial Activity: A New Generation of Flooding Agents for Enhanced Oil Recovery

Enhanced oil recovery (EOR) has become a widely applied technique to meet global energy demands, in which surfactants have been recognized as an important type of efficient EOR agent. However, the application of surfactants in EOR has been subjected to many problems, such as unsatisfactory interfacial activity, high adsorption loss, poor salt resistance, low water solubility, and toxic side effects. In this work, natural long-chain fatty acid oleic acid (OA) and a composite surfactant system with high interfacial activity, formed by OA combining green surfactants coconut diethanolamide (CDEA) and cocamidopropylamine oxide (CAO), were encapsulated through microcapsules prepared by solvent evaporation, which is easy for large-scale production, with the use of ethyl cellulose (EC) as the sustainable shell material. Molecular dynamics (MD) simulations were employed to explore the interfacial behaviors of EC and the surfactants, revealing the mechanisms and providing guidance for core material formula design. It was confirmed that EC formed a stable shell by self-assembly, endowing the microcapsules with oil-targeted performance and surfactant protection. The microcapsules remained stable in brine while ruptured upon encountering the oil phase, releasing the surfactants in situ, and the interfacial tension (IFT) could be reduced by 2-3 orders of magnitude quickly. Microencapsulation of green surfactants not only avoids adsorption and precipitation losses during transport but also overcomes the problem of poor water solubility faced by surfactants with long hydrophobic tails. This study proposes a green and novel strategy for the efficient utilization of surfactants, which provides new ideas and methods for the sustainable development of related industrial fields.