Control of aluminum cross-linked polyacrylamides for sweep improvement

Claim 1

A method of treating a subterranean formation, comprising the steps of sequentially injecting into the formation: (a) an aqueous solution of a cross-linkable polymer; (b) an aqueous solution of a cross-linking agent comprising multivalent cations suitable for cross-linking the polymer and sequestering anions; and (c) an aqueous solution of a salt comprising cations selected from the group consisting of alkali metal cations and sequestering anions.

Claim 2

A method of treating a subterranean formation, comprising the steps of sequentially injecting into the formation: (a) an aqueous solution of a cross-linkable polymer; (b) an aqueous solution of a cross-linking agent comprising multivalent cations suitable for cross-linking the polymer and sequestering anions; and (c) an aqueous solution of a salt comprising cations selected from the group consisting of alkali metal cations and sequestering anions.

Claim 4

The method of claims 1 or 2 wherein said cross-linkable polymer is selected from the group consisting of: polyacrylamide, partially hydrolyzed polyacrylamide, polysaccharide, carboxymethylcellulose, polyvinyl alcohol, polystyrene sulfonates, polyacrylonitrile, polyacrylic acid, polyvinyl pyrrolidone, copolymers of acrylonitrile with acrylic acid and 2-acrylamido-2-methyl-1-propane sulfonic acid; said multivalent cations are selected from the group consisting of: Fe 2+ , Fe 3+ , Al 3+ , Ti 4+ , Zn 2+ , Sn 4+ , Ca 2+ , Mg 2+ and Cr 3+ ; said sequestering anions are selected from the group consisting of: ethylenediaminetetraacetic acid, acetate nitrilotriacetate, tartrate, citrate, tripolyphosphate, metaphosphate, gluconate, and orthophosphate; and said alkali metal cation is selected from the group consisting of: potassium and sodium.

Claim 5

The method of claims 1 or 2 wherein said cross-linkable polymer is polyacrylamide, said cross-linking agent is aluminum citrate and said salt is sodium citrate.

Claim 6

The method of claims 1 or 2 wherein said aqueous solution of a cross-linkable polymer is a solution of mildly sheared polyacrylamide containing from about 100 ppm to about 10,000 ppm by weight polyacrylamide; said aqueous solution of a cross-linking agent is a solution of aluminum citrate containing from about 100 ppm to about 5000 ppm by weight aluminum citrate; and said aqueous solution of a salt comprises a solution of sodium citrate, the concentration of which is determined by the concentration of divalent cations in the formation.

Claim 10

A method of displacing oil through a subterranean oil-bearing formation having high permeability portions therein, said formation being penetrated by at least one producing well, comprising the steps of sequentially injecting into said formation: (a) an aqueous solution of a cross-linkable polymer; (b) an aqueous solution of a cross-linking agent comprising multivalent cations and sequestering anions; (c) an aqueous solution of a salt comprising alkali metal or ammonium cations and sequestering anions; and (d) an aqueous fluid into said formation and displacing oil toward said producing well.

Claim 11

A method of displacing oil through a subterranean oil-bearing formation having high permeability portions therein, said formation being penetrated by at least one producing well, comprising the steps of sequentially injecting into said formation: (a) an aqueous solution of a cross-linkable polymer; (b) an aqueous solution of a cross-linking agent comprising multivalent cations and sequestering anions; (c) an aqueous solution of a salt comprising alkali metal or ammonium cations and sequestering anions; and (d) an aqueous fluid into said formation and displacing oil toward said producing well.