Breaker system for fracturing fluids used in fracturing oil bearing formations

A method of fracturing a zone of a subterranean formation penetrated by a well bore, comprising the steps of:

• forming a gelable fracturing fluid by combining an aqueous base fluid and a hydratable polymer, the pH of the gelable fracturing fluid being greater than about 7.0;
• adding a transition metal crosslinker to the aqueous base fluid for crosslinking the hydratable polymer to form a gelled fluid of sufficient viscosity to facilitate fracturing of the formation;
• adding to the fluid, as a primary breaker, a traditional encapsulated oxidant breaker;
• injecting the gelled fluid into the well bore and into contact with the formation under sufficient pressure to fracture the formation;
• and
• wherein the gelable fracturing fluid has incorporated therein as a companion breaker for the encapsulated oxidant a delayed release breaker comprising a chelating agent that is released slowly over a period of time to compete with the polymer for the transition metal crosslinker, thereby reducing the viscosity of the fluid.