Spontaneous imbibition and interface synergistic effect of surfactants on oil-wet tight sandstone

In order to explore the ability of different surfactants to improve the oil displacement effect by imbibition of oil-wet tight reservoirs, the oil displacement efficiency by imbibition of 17 surfactants in four categories including anionic, non-ionic, cationic, and amphoteric were systematically compared. The differences and mechanism of different types of surfactants on imbibition and oil displacement of tight reservoirs were analyzed. The surfactant formulations for high efficiency displacement of tight reservoirs were developed, and the boundaries of interfacial tension (IFT) and contact angle (CA) properties for high oil-displacement efficiency of tight reservoirs were established. The results show that the oil displacement efficiency by imbibition of anionic and non-ionic surfactants for tight core is 18. 4%~27. 2% under the current experimental condition, which is significantly higher than 0~2. 4% of cationic and amphoteric surfactants. The cationic or amphoteric surfactants alone are not suitable as agents for oil displacement by imbibition in oil-wet tight reservoirs. The ability to regulate wettability is the main reason for the efficient oil displacement by imbibition of surfactants, and there is a synergistic effect between IFT and CA. The efficiency of oil displacement reaches over 38% by imbibition for composite imbibition oil displacement agent. The CA and IFT of surfactants for efficient oil displacement by imbibition from tight reservoirs are 15°~35°, 0. 1~2 mN·m-1, respectively. And the corresponding NB-1 is over 15, indicating that capillary force is the main driving force for imbibition under such conditions. © 2024 University of Petroleum, China. All rights reserved.