The Effects of Crude Oil Gravity and Composition on EOR Surfactants Selection and Performance

Abstract

Abstract Surfactant applicability for enhanced oil recovery (EOR) is conventionally characterized by their efficiency in reducing oil/water interfacial tension (IFT). A suitable surfactant for one crude oil might not be suitable for 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 various EOR 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 high temperatures. The gravities of tested crude oil samples ranged from 8 to 37° API. Crude oil properties were validated using viscometer and density meter. The experimental work focused on IFT measurement and critical micelle concentrations (CMC). IFTs were measured using a spinning drop tensiometer at a fixed concentration and CMCs were determined using a Du Noüy ring type tensiometer. CMCs of the amphoteric and nano-encapsulated-ionic surfactants were found very low compared to that of cationic and nonionic surfactants. Both amphoteric and nano-encapsulated-ionic surfactants demonstrated superior results across all benchtop studies. They have exhibited a better temperature stability with 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 but gradually increased to 0.18 mN/m for the heaviest crude. In terms of IFT equilibration, the amphoteric and nano-encapsulated-ionic surfactants resulted in IFT values that gradually increased with the increase of oil viscosity. This was quite opposite for the cationic quaternary ammonium and anionic alfa olefin sulfonate surfactants. The different behavior of surfactants with crude oils of varying compositions indicate the 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 a low IFT. Coupled with CMC measurements at elevated temperatures, a good insight can be established for evaluating the performance and potential of a surfactant for EOR application.