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 im-bibition 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 signifi-cantly 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 sur-factants for efficient oil displacement by imbibition from tight reservoirs are 15°～35°,0.1～2 mN·m-1,respectively.And the corresponding N-1B is over 15,indicating that capillary force is the main driving force for imbibition under such conditions.
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