Hydraulic fracturing

Claim 1

A method according to claim 1 wherein said aqueous gel comprises water to which there has been added: from 0.0025 to 5 percent of said polymer, based upon the weight of said water; from 0.05 to 60 weight percent of said polyvalent metal compound based upon the weight of said polymer; 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; and wherein the initial total dissolved solids content of said water is not greater than about 60,000 ppm by weight, and of said dissolved solids, the amount of polyvalent metal ions present is not greater than about 6,000 ppm by weight.

Claim 23

A method of fracturing a subterranean formation penetrated by a wellbore, which method comprises, in combination, the steps of: A. forming a base fracturing fluid by adding to a given quantity of water from 0.01 to 1.5 weight percent, based on the weight of said water, of a polymer selected from the group consisting of: polyacrylamides and polymethacrylamides wherein up to about 75 percent of the carboxamide groups can be hydrolyzed to carboxyl groups; crosslinked polyacrylamides and crosslinked polyacrylamides 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 one to four 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 of said polymers; B. adding to said base fracturing fluid one of (a) from 0.5 to 40 weight percent of a water-soluble compound of chromium wherein the valence of the chromium is +6 and which is sufficient to gel said water when the valence of at least a portion of said chromium is reduced from +6 to +3, or (b) from 0.5 to at least about 150 percent of the stoichiometric amount of a water-soluble reducing agent which is effective to reduce the valence of said chromium from +6 to +3; C. pumping a slug of said base fracturing fluid of step (B) down said well and into said formation under a pressure sufficient to create a fracture in said formation; and D. during said pumping adding to said base fracturing fluid the other of said reagents (a) and (b) which was not added thereto in said step (B).