Prediction of the Aqueous Stability Limit of Surfactant EOR Formulations

A new structure-property model was developed to predict the aqueous stability limit of chemical EOR formulations from the surfactant and co-solvent structures. The coacervation of aqueous solutions is modeled in a way that is similar to that of phase transitions for microemulsions but excluding the effect of oil. In addition to modeling the effects of surfactant structure, co-solvent partitioning and structure, and the interactions of divalent cations with anionic head groups, the effect of polymer concentration and the interactions of surfactant lipophiles were modeled. A new aqueous stability dataset consisting of 858 aqueous stability experiments with various combinations of 121 surfactants (internal olefin sulfonates, alkylbenzene sulfonates, alcohol alkoxy sulfate, and alcohol alkoxy carboxylate) and 19 co-solvents (alcohols and alcohol alkoxylates) was used for model development and cross validation. The structures of the surfactants and co-solvents in the new dataset include variations in the type of hydrophobe (carbon number, degree of branching, polydispersity, and aromaticity), number of alkoxylate groups (propylene oxide and ethylene oxide), and the type of head group. The structure-property models for the optimum salinity and optimum solubilization ratio (Chang et al., 2019) can be used with the new structure-property model for the aqueous stability limit to provide a useful guide to experimental testing programs for the development of chemical formulations for enhanced oil recovery and other similar applications requiring both low interfacial tension and aqueous stability.