If you are referring to this paper: Feasibility Study of Crude Oil Mobilization Using Nanoemulsion in Low Oil Saturation Reservoirs, we employed nuclear magnetic resonance (NMR) and heavy water (which does not produce an NMR signal). The NMR signals scanned at different time points vary, reflecting changes in oil content. This serves as the basis for our study. Additionally, in such research, due to the density difference between oil and water, the oil-water interface can be clearly observed after waiting a moment.