Patent ID: 7749941

Claim:
A method for drilling a borehole in a subterranean formation having temperatures greater than 250° F., said method comprising drilling a borehole in the subterranean formation; employing an aqueous based, clay-free, drilling fluid in said drilling operation, said fluid comprising a water soluble polymer viscosifier or rheology control agent; and enhancing the tolerance of said fluid to said temperatures by adding to or including in said fluid a diacid or diacid salt in the range of about 5 lb/bbl to less than 10 lb/bbl, at a pH of greater than 7, wherein said diacid or diacid salt has about two to about eight carbon atoms, said diacid has a formula: where M + is a cation and x equals a number from 0 to 6; wherein all diacid salt in said fluid is selected from the group of oxalate salts consisting of sodium oxalate, lithium oxalate, potassium oxalate, and calcium oxalate; wherein said water soluble polymer is a viscosifier selected from the group of polymers consisting of celluloses, cellulose derivatives, Scleroglucan polysaccharides, and Xanthan polysaccharides and other biopolymers.