Desorption of hydrocarbon molecules encapsulated with cationic and nonionic surfactants under flow as a model for enhanced oil recovery

Enhancing oil recovery from mature reservoirs remains a critical challenge due to strong adsorption of hydrocarbons onto rock surfaces. Surfactant injection offers a viable strategy to desorb oil molecules from surfaces. Here we report nonequilibrium, mesoscale numerical simulations under stationary Poiseuille flow to investigate the desorption of adsorbed hydrocarbons from model surfaces with varying adsorption strengths with ionic and nonionic surfactants. A novel, molecularly detailed model for oil is introduced, made up of light and heavy hydrocarbon molecules. The desorption efficacy of ionic and nonionic surfactants is evaluated across different concentrations. The viscosity is extracted from simulations and it is found that the nonionic surfactant induces higher viscosity in the system than the cationic surfactant. The results show that ionic surfactants achieve superior desorption by forming multilayer structures that encapsulate hydrocarbons into spherical aggregates, leading to lower contact area, lower viscosity and enhanced extraction, even at low concentrations. In contrast, nonionic surfactants form monolayers that fragment hydrocarbons into smaller aggregates, increasing system viscosity and hindering extraction. Desorption isotherms as functions of surfactant concentration are predicted for both surfactant types. These findings provide molecular insights to guide surfactant design and selection for enhanced oil recovery applications.