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US 5,224,546 AGranted
Method of breaking metal-crosslinked polymers
OwnerWilliam H. Smith, Jimmie D. Weaverinventors
Life of this patent
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Abstract
A new method is provided for improved degradation of metal-crosslinked polymer gels which are useful in oil and gas well treating operations. In this method an esterified carboxylated chelator is added to the gel. At elevated temperatures, the esterified chelator undergoes hydrolysis to form an acid and an active ligand which subsequently removes the crosslinking metal ion from the gel and hydrolyses the polymer.
Claims13
A method of treating a subterranean formation comprising the steps of:
- placing a viscous crosslinked polymer gel composition into said formation comprised of an aqueous fluid, a polymer, a metal ion polymer crosslinker and a hydrolyzable carboxylated chelating agent ester which hydrolyzes upon being heated by said formation selected from the group consisting of ethylenediaminetetraacetic acid esters, nitrilotriacetic acid esters, citric acid esters and hydroxyacetic acid esters, said carboxylated chelating agent ester having a chemical association with said metal ion which is less than the chemical association of said polymer with said metal ion, but the carboxylated chelating agent released when said ester is hydrolyzed having a chemical association with said metal ion which is greater than the chemical association of said crosslinked polymer with said metal ion whereby said polymer is uncrosslinked and the viscosity of said composition is reduced;
- and
- removing said composition from said formation after said carboxylated chelating agent ester has hydrolyzed and said released carboxylated chelating agent has chemically associated with said metal ion whereby said composition has converted to a lower viscosity fluid.
A method of fracturing a subterranean formation penetrated by a well bore comprising the steps of:
- pumping a viscous crosslinked polymer fracturing fluid composition into said formation at a pressure sufficient to fracture said formation, said fracturing fluid composition comprising an aqueous fluid, a polymer, a metal ion polymer crosslinker and a hydrolyzable aminopolycarboxylated chelating agent ester which hydrolyzes upon being heated by said formation, said aminopolycarboxylated chelating agent ester having a chemical association with said metal ion which is less than the chemical association of said polymer with said metal ion, but the aminopolycarboxylated chelating agent released when said ester is hydrolyzed having a chemical association with said metal ion which is greater than the chemical association of said crosslinked polymer with said metal ion whereby said polymer is uncrosslinked and the viscosity of said composition is reduced;
- and
- removing said composition from said formation after said formation has been fractured, said aminopolycarboxylated chelating agent ester has hydrolyzed and the released aminopolycarboxylated chelating agent has chemically associated with said metal ion whereby said composition has converted to a lower viscosity fluid.
Dependencies are inferred from the claim text.