Crosslinking water soluble polymers with iron to form gels for use in subterranean profile modification

Claim 1

In a method for altering the permeability of at least a portion of a subterranean formation wherein a fluid gelable composition is passed into the formation to a preselected location and the composition is gelled to modify the fluid flow profile of said portion of the formation, the improvement comprising using as the fluid gelable composition a composition comprising: (a) water (b) a water-thickening and cross-linkable amount of a water-dispersible polysaccharide or a polymer consisting essentially of: (i) from about 3 to 100 mole percent of acrylic monomer units or salts thereof and (ii) from about 97 to 0 mole percent of other water-soluble monomer units or salts thereof and (c) an amount of a polyvalent metal capable of cross-linking said polymer to form a stable gel, said polyvalent metal being provided in the form of a redox couple, said redox couple comprising (iii) at least one water-soluble ferrous reducing agent capable of being oxidized to a higher valence state and (iv) an oxidizing agent effective to oxidize ferrous ion to ferric ion whereby said polyvalent metal is in situ produced in the form of ferric ion by oxidation of said reducing agent by said oxidizing agent.