Composition and the use thereof for reducing the permeability of a formation

Claim 2

The method of claim 1 wherein one of said cross-linking agents consists of at least one multivalent inorganic cation which forms a hydroxide precipitate from a 0.02 molar solution of said cation when the pH of said solution is adjusted to a value of between about 7 and about 4, and the second cross-linking agent consists of at least one organic compound which is effective to cross-link the water-soluble polymer at a pH of about 3 or lower, said pH of said solution being between the effective pH values of said cross-linking agents.

Claim 3

The method of claim 3 wherein the inorganic multivalent cation consists of at least one of Nd, Zn, Co, Cd, Ni, Yb, Pb, Be, Fe 2, Cu, Cr 3, VO 2, VO2 2, or Al, and the organic cross-linking agent consists of a low molecular weight water-soluble aldehyde, or a water-soluble derivative thereof which is effective to cross-link said organic polymer in an aqueous solution having a pH of about 3 or lower.

Claim 4

The method as defined in claim 3 wherein the inorganic multivalent cation is aluminum or chromium and the organic compound is formaldehyde, paraformaldehyde or glyoxal.

Claim 5

The method of claim 3 wherein the cross-linkable water-soluble polymer is an anionic acrylamide polymer.

Claim 6

In the method of modifying water injection well profile and decreasing the water/oil ratio in the total well effluent from a production well consisting of injecting into the formation in the injection well or producing well a substantial quantity of an aqueous solution of a cross-linkable water-soluble anionic organic polymer the improvement which comprises: a. including in said aqueous solution of said polymer at least one dissolved polyvalent metal cation characterized as forming a metal hydroxide precipitate from a 0.02 molar solution of said cation when the pH is adjusted to a value between about 7 and 4 and at least one organic compound which is effective to cross-link the polymer at a pH of 3 or lower, b. providing a pH value in said aqueous solution of said polymer between the effective cross-linking pH value of said cross-linking agents, and c. adjusting the pH value of said aqueous solution after it has been injected into said formation to a value which is effective to cross-link said polymer.

Claim 7

The method of claim 1 wherein the effective pH values differ by a numerical value of at least about 2.

Claim 8

The method of claim 2 wherein the effective pH values differ by a numerical value of at least about 2.

Claim 9

The method of claim 4 wherein said cross-linking agents have effective pH values differing by at least about 2.

Claim 10

The method of claim 7 wherein the cross-linking agents have effective cross-linking pH values differing by a numerical value of at least about 2.