Sodium silicate cementing prepad flushing fluid

The invention discloses a sodium silicate cementing prepad flushing fluid, which comprises a flushing fluid, a spacer fluid and an aqueous sodium silicate solution with concentration of 25-55wt. %. Based on the existing cementing prepad flushing fluid, a sodium silicate solution is added, and the activation of sodium silicate on silicon and aluminum oxides and the like is utilized to improve the cementing strength of oil well cement as well as casing walls and well walls and resist the corrosion capacity of carbon dioxide and hydrogen sulfide to the surface of a casing; the sodium silicate percolates through a well wall mud cake and a soft clay layer to be chemically combined with calcium and magnesium salts and the like to form calcium and magnesium silicate and other silicone gel flocculates, the loose clay layer is solidified, the swelling and collapse of mud shale of a stratum are prevented, and the quality of well wall mud cake is improved. The sodium silicate cementing prepad flushing fluid provided by the invention has the advantage that except the cleaning effect of the original prepad flushing fluid is kept, the cementing strength of a cement wall interface can also be enhanced, and thus the cementing quality requirement is met.