Patent ID: 7093659

Claim:
A method of treating a subterranean formation penetrated by a well, the method comprising the steps of: (a) forming a treatment fluid comprising: 1) water having a magnesium ion concentration of less than 1 mM and a calcium ion concentration of less than 2.5 mM; 2) a water-soluble polysaccharide capable of increasing the viscosity of the water and present in a sufficient concentration to increase the viscosity of the water; and 3) a breaker comprising at least one member selected from the group consisting of a source of chlorite ions and a source of hypochlorite ions, wherein the breaker is present in a sufficient concentration to break the viscosity of the treatment fluid after introduction of the fluid into the subterranean formation; (b) at any stage of forming the treatment fluid, adding a breaker moderator comprising at least one member selected from the group consisting of a source of magnesium ions and a source of calcium ions to provide a sufficient concentration of the breaker moderator to reduce the break rate of the fluid compared to the treatment fluid without the addition of the breaker moderator; and (c) introducing the treatment fluid into the well and into contact with the formation.