Spontaneous imbibition is an effective method to improve the oil recovery of tight reservoirs.The development and research of nano-emulsion provide a new technical direction for improving spontaneous imbibition oil recovery (SIOR) in tight reservoirs.The salinity has a significant effect on the properties and spontaneous imbibition of nano-emulsion, but the effect on the imbibition mechanisms is still unclear.In the paper, thelower nano-emulsion system with core-shell structures, called HS-LNE,is prepared by nano-emulsion dilution method.Afterwards,the properties and imbibition mechanisms of HS-LNE under different salinitiesare studied.Firstly,the particalsize andstability of the HS-LNE system are evaluated by centrifugation and spectroscopy. What's more, the interfacial tension (IFT), wettability,and adsorption experiments under diffierent salinitiesare carried out, and the salinity influences on the physicochemical properties of the HS-LNE system is systematically analyzed.At the same time, the SIORvariationlaw of the HS-LNE system under different salinitiesis comprehensively explored through static spontaneous imbibition experiments.The experimental results show that the HS-LNE system has excellent stability at high salinity. Moreover, as the salinity increasing, the IFT of the HS-LNE system decreased, and the wettability alternationincreased.However, the adsorption on solid interfaceswas not significantly changed and SIOR reached the highest value of 50.27% at the optimal salinity (50×103mg/L). Finally, the HS-LNE system with the optimal salinity was selected for the field test forpermeability enhancement and flooding in Well Gan 128 in Jilin Oilfield. The oil production was increased by 450 t after 5 months, with an estimated validity period of 24 months and a cumulative oil production increase of 1900 t.

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