Application of the Hydrophilic–Lipophilic Deviation Concept to Surfactant Characterization and Surfactant Selection for Enhanced Oil Recovery

Abstract The hydrophilic–lipophilic deviation (HLD) concept has been demonstrated to be useful in determining characteristic curvature (Cc) of a surfactant. Cc is a surfactant parameter that reflects the hydrophobicity/hydrophilicity or the tendency of the surfactant to form microemulsions in an oil–water system. In order for the Cc value to be calculated, the formation of the optimum Winsor III microemulsion of oil and water systems under specific salinity and temperature conditions is required. Surfactant Cc values have been widely used to quantitatively screen and select a suitable surfactant in formulations for different application areas, especially enhanced oil recovery (EOR). The HLD concept is an effective tool for designing new surfactant molecules to meet the target Cc value for a specific formulation condition. The HLD equation indicates the dependence of a microemulsion system on the changes of various system parameters. This article demonstrates how the HLD equation can be derived in different ways depending on the characteristics of the surfactant to identify the proper experimental approach so that the Cc values of different types of surfactants can be determined. Three types of surfactants were studied, including nonionic alcohol ethoxylates, anionic alkyl propoxy ethoxy sulfates, and carboxylates. The application of the HLD concept to surfactant selection for EOR application was also demonstrated.