A process for the selective and controlled reduction of permeability to
water in oil-bearing formations made up of sandstone or limestone, the process comprising the injection of a
slug of
polymer aqueous solutions having a polarity opposite to the polarity of the rock, followed by the injection of a spacing
slug of alkaline
halide and then a fresh
slug of
polymer aqueous solution, the polarity of which is opposite to the polarity of the first
polymer slug, and then a slug of
aqueous solution of trivalent
metal crosslinking agent to effect the partial crosslinking of the polymer charges, the polymer
layers being successively added until the
injection pressure of the polymer aqueous solutions show that the desired Residual Resistance Factor RRF was attained, and well production may be resumed.