IFT or wettability alteration: What is more important for oil recovery in oil-wet formation?

Several researchers have investigated the dominant recovery mechanisms among the wettability alteration and interfacial tension (IFT) reduction during surfactant flooding in unconventional, oil-wet reservoirs. Most of the previous studies carried out using spontaneous imbibition fail to answer the dominance of prominent mechanisms, especially with respect to time and location. In this paper, these research gaps are addressed through physico-chemical interactions, and microfluidic studies carried out using zwitterionic surfactant solutions of varying alkyl length and salinity. Based on the IFT and zeta potential values, three surfactant formulations (F1, F2 and F3) are chosen for representative carbonate microfluidic studies. The observations of microfluidic studies are significant to emphasize that at early time F2 and F3 formulation corresponded to higher imbibition rate than F1 formulation due to its higher ability to alter the rock wettability from oil-wet to water-wet. As the front propagates to far location, F1 with ultra-low IFT begins to outperform F3 by providing better microscopic displacement and quicker frontal propagation throughout. In the water-wet media, F1 formulation with the lowest IFT outperforms other formulations at all the time. The results of the study signify that while significant IFT reduction is sufficient for the complete oil displacement in water-wet media, significant IFT reduction at later stage and good wettability alteration at the early stage are needed during surfactant flooding in oil-wet formation.