Patent ID: 7208529

Claim:
A method for breaking the viscosity of polymer gelled aqueous fluids comprising a borate crosslinked guar or a borate crosslinked derivatized guar polymer gel, the method comprising adding an effective amount of at least one aminocarboxylic acid to break down the gel by acting on the crosslinker and primarily directly on the polymer gel, where the aminocarboxylic acid is selected from the group consisting of ethylenediaminetetraacetic acid (EDTA), propylenediaminetetraacetic acid (PDTA), hydroxyethylenediaminetetraacetic acid (HEDTA), nitrilotriacetic acid (NTA), ethylenediaminetriacetic acid (HEDTA), ethylenediaminediacetic acid (H 2 EDDA), dihydrate ethylenediaminediacetic acid (2H 2 O EDTA), salts of these acids, and mixtures thereof; where the method is conducted at a temperature between about 120° F. (49° C.) and about 280° F. (138° C.) and in the absence of an oxidizer or an enzyme effective to break viscosity within this temperature range.