Method and composition for delaying the gellation of borated galactomannans

A method of controlling the cross-linking reaction of an aqueous fracturing fluid in fracturing a subterranean formation, comprising the steps of:

• blending together an aqueous fluid and a hydratable polymer capable of gelling in the presence of borate ions;
• allowing the polymer to hydrate to form a hydrated polymer sol;
• adding an alkaline buffer to thereby adjust the pH of the hydrated polymer sol in the range from about 8.0 to 11.5;
• forming a complexor solution for said hydrated polymer gel by combining a cross-linking additive capable of furnishing borate ions in solution with a delay additive selected from the group consisting of dialdehydes having about 2-4 carbon atoms, keto aldehydes having about 3-4 carbon atoms hydroxyl aldehydes having 2-4 carbon atoms, ortho substituted aromatic dialdehydes and ortho substituted aromatic hydroxyl aldehydes, the delay additive being effective, to chemically bond wit the borate ions and boric acid produced by the cross-linking additive to thereby limit the number of borate ions available in solution for subsequent cross-linking of the hydrated polymer sol;
• adjusting the pH of the complexor solution to achieve a desired delay in the cross-linking reaction of the hydrated polymer gel, the delay achieved being a function of the complexor solution pH, wherein upward adjustment of the pH of the complexor solution serves to retard the rate of the subsequent cross-linking of the hydrated polymer sol while downward adjustment of the pH of the complexor solution serves to accelerate the rate of subsequent cross-linking;
• and
• adding the complexor solution to the hydrated polymer sol to cross-link the hydrated polymer sol.