Method for imparting selectivity to otherwise nonselective polymer control gels

A method for the sequential gellation profile control treatment of a formation having zones of varying permeabilities comprising:

• (a) making an aqueous gellable mixture containing components for a transition metal cross-linked Xanthan biopolymer first stage ex-situ gel in an amount sufficient to selectively enter pores in a formation's zone of greater permeability;
• (b) placing into said aqueous mixture a second gellable mixture sufficient to form an in-situ gel comprised of;
• (i) about 0.2 to about 5.0 wt. percent of a cross-linkable polymer which is a member selected from the group consisting of polyacrylamide, polyvinyl alcohol, poly(acrylamide-co-acrylamido-2-methyl-propane-sulfonate), a copolymer of N-vinyl-2-pyrrolidone and acrylamide, a copolymer of polyacrylamide and methylene-bis-acrylamide, a terpolymer of AMPS, vinylacylamide, and acrylamide, acrylamide modified polyvinyl alcohol and mixtures thereof having at least one functional group selected from a member of the group consisting of an amine, an amide, a hydroxyl, or a thiol group, and
• (ii) 0.02 to 50.0 wt. percent of a partially methylated aminoplast resin or an organic cross-linker and mixtures thereof which cross-link with said polymer in-situ thereby forming a non-selective second stage gel;
• (c) allowing the aqueous mixture sufficient time to form ex-situ said first stage gel;
• and
• (d) injecting said first stage gel containing said second gellable mixture into said zone of greater permeability where said first stage gel selectively enters the zone of greater permeability, reheals and forms under formation conditions a solid gel having the characteristics of the in-situ gel which gel is substantially more resistant to formation conditions than said first stage gel.