Nano liquid for decompression and augmented injection of tight oil water-flooding and preparation method and application thereof

The present invention relates to a nano liquid for decompression and augmented injection of tight oil water-flooding, and a preparation method and application thereof. The nano liquid for decompression and augmented injection is composed of 0.1-1% of hydrophobic nano-silica, 0.3-3% of a dispersant, 0.2-1% of a dispersing aid and the balance of water. The hydrophobic nano-silica has particle size between 12-22 nm, and median diameter between 16-18 nm; and the hydrophobic nano-silica is prepared from fumed nano silica and an organic silicon compound by a wet modification method. The dispersant is octylphenyl polyoxyethylene ether, polyethylene glycol 400, polyethylene glycol 600 or glycerin. The dispersing aid is NaOH, Na2SiO3 or n-butanol. The nano liquid for decompression and augmented injection employs water base dispersion and has the advantages of environment-friendliness, simple preparation and good stability. Under the action of stratum water salt ions, the hydrophobic nano-silica is adsorbed on the surface of the rock, so that wetting conversion generates on the rock surface to produce hydrophobic slip effect and reduce flow resistance and injection pressure.