Method for reducing formation permeability with gelled polymer solution having delayed gel time

Claim 3

A method according to claim 1 wherein said first mixture is an aqueous solution having a polymer concentration in the range of about 250 ppm to about 20,000 ppm, and said multivalent metal compound is sodium dichromate present in a concentration in the range of about 10 ppm to about 2500 ppm.

Claim 4

A method according to claim 1 wherein the water of said first mixture is one of fresh water on brine.

Claim 5

A method according to claim 1 wherein said complexing agent is one of citrate, acetate, or arsenate.

Claim 6

A method according to claim 1 wherein said complexing agent is citric acid.

Claim 7

A method according to claim 1 wherein said second mixtuRe has a complexing agent concentration in the range of about 5 ppm to about 5000 ppm.

Claim 8

A method according to claim 1 wherein said reducing agent is sodium hydrosulfite.

Claim 9

A method according to claim 1 wherein said third mixture has a reducing agent concentration in the range of about 5 ppm to about 2500 ppm.

Claim 10

A method according to claim 1 wherein: said polymer is a carboxymethyl cellulose and the concentration thereof in said first mixture is within the range of from 250 to 20,000 ppm; said multivalent metal compound is sodium dichromate and the concentration thereof in said first mixture is within the range of from 10 to 2500 ppm; said complexing agent is citric acid and the concentrations thereof in said second mixture is within the range of from 5 to 5,000 ppm; and said reducing agent is sodium hydrosulfite or sodium bisulfite and the concentration thereof in said third mixture is within the range of from 5 to 2500 ppm.

Claim 11

In a method wherein an aqueous gel is introduced into a borehole in the earth and into a subterranean formation penetrated by said borehole, the improvement wherein said aqueous gel has an extended gelation time and comprises water to which there has been added: a water-thickening amount of a water-dispersible polymer selected from the group consisting of (a) water-soluble cellulose ethers, (b) polyacrylamides and polymethacrylamides wherein up to about 75 percent of the carboxamide groups can be hydrolyzed to carboxyl groups; crosslinked polyacrylamides and crosslinked polymethacrylamides wherein up to about 75 percent of the carboxamide groups can be hydrolyzed to carboxyl groups; polyacrylic acid and polymethacrylic acid; polyacrylates; polymers of N-substituted acrylamides wherein the nitrogen atoms in the carboxamide groups can have from 1 to 2 alkyl substituents which contain from 1 to 4 carbon atoms; copolymers of acrylamide with another ethylenically unsaturated monomer copolymerizable therewith, sufficient acrylamide being present in the monomer mixture to impart said water-dispersible properties to the resulting copolymer when it is mixed with water, and wherein up to about 75 percent of the carboxamide groups can be hydrolyzed to carboxyl groups; and mixtures thereof; and (c) a biopolysaccharide produced by the action of bacteria of the genus Xanthomonas on carbohydrates; an amount of a water-soluble compound of a polyvalent metal wherein the metal present is capable of being reduced to a lower polyvalent valence state and which amount is sufficient to cause gelation of said water containing said polymer when the valence of at least a portion of said metal is reduced to said lower valence state; an amount of a complexing agent capable of complexing with ions of said metal in said reduced valence state; and sufficient to complex with at least a portion of said ions and cause said extended gelation time; and an amount of a water-soluble reducing agent which is effective to reduce at least a portion of said metal to said lower valence state, with said reducing agent being added to said water after said complexing agent has been added thereto.

Claim 12

In a method wherein an aqueous gel is introduced into a borehole in the earth and into a subterranean formation penetrated by said borehole, the improvement wherein said aqueous gel has an extended gelation time and comprises water to which there has been added: a water-thickening amount of a water-dispersible polymer selected from the group consisting of (a) water-soluble cellulose ethers, (b) polyacrylamides and polymethacrylamides wherein up to about 75 percent of the carboxamide groups can be hydrolyzed to carboxyl groups; crosslinked polyacrylamides and crosslinked polymethacrylamides wherein up to about 75 percent of the carboxamide groups can be hydrolyzed to carboxyl groups; polyacrylic acid and polymethacrylic acid; polyacrylates; polymers of N-substituted acrylamides wherein the nitrogen atoms in the carboxamide groups can have from 1 to 2 alkyl substituents which contain from 1 to 4 carbon atoms; copolymers of acrylamide with another ethylenically unsaturated monomer copolymerizable therewith, sufficient acrylamide being present in the monomer mixture to impart said water-dispersible properties to the resulting copolymer when it is mixed with water, and wherein up to about 75 percent of the carboxamide groups can be hydrolyzed to carboxyl groups; and mixtures thereof; and (c) a biopolysaccharide produced by the action of bacteria of the genus Xanthomonas on carbohydrates; an amount of a water-soluble compound of a polyvalent metal wherein the metal present is capable of being reduced to a lower polyvalent valence state and which amount is sufficient to cause gelation of said water containing said polymer when the valence of at least a portion of said metal is reduced to said lower valence state; an amount of a complexing agent capable of complexing with ions of said metal in said reduced valence state; and sufficient to complex with at least a portion of said ions and cause said extended gelation time; and an amount of a water-soluble reducing agent which is effective to reduce at least a portion of said metal to said lower valence state, with said reducing agent being added to said water after said complexing agent has been added thereto.

Claim 13

A method according to claim 10 wherein there has been added to said water: from 0.025 to 5 weight percent of said cellulose ether, based upon the weight of said water; from 0.05 to 40 weight percent of said compound of a polyvalent metal, based upon the weight of said cellulose ether; from 10 to 300 weight percent of said complexing agent, based upon the weight of said polyvalent metal compound; and from 0.1 to at least about 200 percent of the stoichiometric amount of said reducing agent required to reduce said polyvalent metal to said lower polyvalent valence state.

Claim 14

A method according to claim 11 wherein: said cellulose ether is a carboxymethyl cEllulose ether; said polyvalent metal compound is a compound of chromium selected from the group consisting of ammonium chromate, ammonium dichromate, the alkali metal chromates and dichromates, chromium trioxide, and mixtures therof; and said reducing agent is selected from the group consisting of sodium sulfide, sodium hydrosulfite, sodium metabisulfite, sodium bisulfite, sodium thiosulfate, potassium sulfide, potassium hydrosulfite, potassium metabisulfite, potassium bisulfite, potassium thiosulfate, and mixtures thereof.

Claim 15

A method according to claim 12 wherein: said cellulose ether is sodium carboxymethyl cellulose; said polyvalent metal compound is sodium dichromate; and said complexing agent is citric acid.

Claim 16

A method according to claim 13 wherein: from 0.025 to 2 weight percent of said cellulose ether has been added to said water; from 2 to 30 weight percent of said sodium dichromate has been added to said water; and from 50 to 250 weight percent of said citric acid has been added to said water.