(478e) Robust Interfacial Tension Measurement and Surfactant Formulation Evaluation Protocol for Enhanced Oil Recovery

Chemical enhanced oil recovery (cEOR) aims to improve the oil recovery rate of mature oil fields. The interfacial tensions (IFTs) between the aqueous phases, the oil phase, and other possible phases from the oil/water mixtures are important for designing and estimating a chemical formulation effectiveness. Furthermore, ultralow (< 10^-2 mN·m^-1) IFTs are targeted to increase the capillary number and help mobilize trapped oil droplets. However, determination of reliable IFT values for surfactant/oil/brine mixtures involving commercial surfactants and crude oil have been avoided, because it is difficult to determine such values mainly due to the complexity of the mixture systems. Here, a robust protocol for determining reliable equilibrium IFT (EIFT) values for a commercial surfactant, crude oil, and synthetic reservoir brine is demonstrated to improve the conventional surfactant formulation design process for target reservoirs. The protocol contains dynamic measurement of IFT values and controlled interfacial area perturbation tests to test the stability of the steady-state IFT values.

Moreover, five types of EIFTs have been defined to establish the relation between the EIFT values of surfactant/oil/brine mixtures and laboratory-scale core flood test results: (I) the un-pre-equilibrated equilibrium IFT; (II) the un-pre-equilibrated EIFTs in the presence of rock; (III) the pre-equilibrated EIFTs in the presence of oil; (IV) the pre-equilibrated EIFT in the presence of rock and oil; and (V) the effluent EIFT. Among the five types of EIFTs, the fourth and fifth were found to be the most relevant for achieving high oil recovery performance in core flood tests, because they capture the effects of surfactant partitioning into the oil phase and the adsorption losses on the rock surface. For instance, for three surfactant formulations tested with Berea core flood experiments, the one with the lowest type-IV EIFT (~0.01 mN·m^-1) had the highest oil recovery ratio (78%), and the one with the highest type IV EIFT (~0.2 mN·m^-1) had the lowest oil recovery ratio (55%). The other EIFTs correlated less well with the oil recovery performance. Identifying surfactant formulations that have low or ultralow EIFTs, especially of type IV or V, are critical for screening formulations appropriate for core flood tests and target field applications, and for predicting oil recovery performance.