Polyphenol-based nanoscale biomass emulsifier and preparation method thereof

The preparation method comprises the following steps: S1, adding dried black wattle tree tannin powder into deionized water, stirring to enable black wattle tree tannin to be dissolved to the maximum extent, then adding acetone, and continuously stirring to enable the black wattle tree tannin to be completely dissolved, so as to obtain a mixed solution; s2, under the stirring condition, slowly dropwise adding the mixed solution into the other part of deionized water, and fully stirring and dissolving to obtain a diluted solution; s3, the diluted solution is treated by a rotary evaporator to remove acetone, and then the obtained solution is subjected to ultrasonic homogenization to obtain the polyphenol-based nanoscale biomass emulsifier. The emulsifier is used as an oil-displacing agent to be injected into a stratum, and the emulsifier and in-stratum crude oil act to form an oil-in-water pickering emulsion; repeated emulsification and demulsification of the pickering emulsion are controlled by adjusting the p