The effects of crude oil gravity and composition on EOR surfactants selection and performance

Surfactant applicability for enhanced oil recovery (EOR) is conventionally characterized by their efficiencyin reducing oil/water interfacial tension (IFT). A suitable surfactant for one crude oil might not be suitablefor another in terms of lowering IFT. Therefore, formulations should be revisited for particular cases, especially with changes in crude oil API gravity. In this work, we investigate the performance of variousEOR surfactants and their behaviors with different crude oil samples from super light to extra heavy. EOR surfactants of different classes showed a suitable compatibility in high salinity brines and at hightemperatures. The gravities of tested crude oil samples ranged from 8 to 37° API. Crude oil properties werevalidated using viscometer and density meter. The experimental work focused on IFT measurement andcritical micelle concentrations (CMC). IFTs were measured using a spinning drop tensiometer at a fixedconcentration and CMCs were determined using a Du Noüy ring type tensiometer. CMCs of the amphoteric and nano-encapsulated-ionic surfactants were found very low comparedto that of cationic and nonionic surfactants. Both amphoteric and nano-encapsulated-ionic surfactantsdemonstrated superior results across all benchtop studies. They have exhibited a better temperature stabilitywith low- and high-salinity brines. Both showed low IFT values around 0.02 mN/m for light crude oil.Those IFT values remained the lowest compared to other surfactants with heavier crude oil samples butgradually increased to 0.18 mN/m for the heaviest crude. In terms of IFT equilibration, the amphotericand nano-encapsulated-ionic surfactants resulted in IFT values that gradually increased with the increaseof oil viscosity. This was quite opposite for the cationic quaternary ammonium and anionic alfa olefinsulfonate surfactants. The different behavior of surfactants with crude oils of varying compositions indicatethe distinctive reaction of each surfactant with a specific crude oil. The results highlight the effects of crude oil gravity and composition on surfactant ability to result in alow IFT. Coupled with CMC measurements at elevated temperatures, a good insight can be established forevaluating the performance and potential of a surfactant for EOR application.