Dynamic Monitoring and Enhanced Oil Recovery Evaluation of the Water Flooding Process of Liquid Nanofluids in Tight Reservoirs

The CT scanning technology can observe fluid saturation distribution in the rock at different times during water flooding in tight reservoirs. However, this technology has not been used to study the water flooding characteristics in changing the wettability of liquid nanofluids. First, this study evaluated the basic properties of a nonionic liquid nanofluid, including the contact angle (CA), interfacial tension (IFT), and aqueous stability tests. Then, the water flooding process in tight rocks is dynamically monitored by the CT scanning technology. The water flooding characteristics of liquid nanofluids changing reservoir wettability are analyzed by measuring the rock's water phase saturation distribution at different times. Finally, the spontaneous imbibition experiment evaluated the enhanced oil recovery of liquid nanofluids. The results show that the particle size of the liquid nanofluid is at the nanometer level (7.5 nm) and can change the wettability of oil-wet to water-wet. Liquid nanofluid has low interfacial tension and can exist stably in brine with a high salinity (20,000-50,000 ppm). In water flooding, the front profile of water phase saturation changes obviously, and it is driven forward with a similar "piston" type. Compared with the brine water, the water invasion front gradually becomes uniform, which is strong evidence that a liquid nanofluid can change the wettability of rocks. Besides, the invasion depth of the fracturing fluid with liquid nanofluids is deeper than that of brine water and displaces more oil. Finally, the spontaneous imbibition test shows that the recovery factor of high-concentration (1 wt %) liquid nanofluids increases by 28.9% compared with that of brine water. This paper provides theoretical support for applying liquid nanofluids in tight reservoirs.