To address the limited understanding of microscopic displacement mechanisms of nanoemulsions in enhanced oil recovery, this study systematically investigated the microscale oil displacement behavior and patterns of a nanoemulsion using in situ computed tomography (CT) scanning technology, combined with performance evaluation and core flooding experiments. The results show that the nanoemulsion has a particle size distribution of 190–280 nm and can reduce the oil–water interfacial tension to the order of 10–3 mN/m. It effectively emulsifies crude oil, reducing the emulsion droplet size to 0.72 μm, and alters wettability by decreasing the contact angle from 111.1° to 6.8°. Core flooding experiments reveal that the oil recovery during primary water flooding increases with a greater permeability contrast and higher displacement rates. In contrast, the recovery during the nanoemulsion flooding stage decreases with increasing permeability but increases with higher displacement rates. The subsequent water flooding stage shows reduced recovery as both the permeability contrast and displacement rate increase. In situ CT analysis indicates that primary water flooding mainly displaces oil along pore margins, while the nanoemulsion exhibits varying displacement efficiency across the pores of different scales, promoting oil phase dispersion and mobilization. Permeability contrast and displacement rate significantly influence the nanoemulsion’s effectiveness in different pore sizes, with lower permeability contrast and lower displacement rates proving more favorable for improving overall oil recovery. These findings provide valuable guidance for the design of nanoemulsion flooding in low-permeability reservoirs.
houyuan et al. (Fri,) studied this question.