A method of gravel packing a well formation and an apparatus usable therefor. The method of gravel packing includes mixing a slurry formed by solids suspended in a gelled carrier fluid with a breaker fluid at a subterranean position above the well formation to be packed, whereby the gel is broken into a low viscosity fluid which is pumped along with the solids to the formation for packing thereof. The apparatus includes a mixing valve positioned in a tool string above a packer, crossover tool and liner screen. When the tool string is run into the well, the mixing valve defines said subterranean position. The breaker fluid is spotted in an annulus between the tool string and well bore, above the packer. The gelled slurry is pumped down the tool string to the mixing valve, and the breaker fluid is introduced through the mixing valve into the tool string for mixing with the gel. The resultant low viscosity fluid and solids are pumped through the crossover tool into the annulus between the liner screen and well formation for packing.
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