Abstract: The invention provides aqueous based well drilling and servicing fluids containing a polymer viscosifier with enhanced thermal stability provided by a diacid or diacid salt preferably having about two to about eight carbon atoms, such as, for example, sodium oxalate. The invention also provides a method of enhancing the thermal stability of aqueous based well drilling and servicing fluids containing a polymer viscosifer by adding diacid or diacid salt to the fluids.

Abstract: Aqueous wellbore treatment fluids having improved thermal stability are provided. The wellbore treatment fluids comprise at least one polysaccharide and an effective amount of at least one polyacrylamide to maintain its stability at a temperature greater than about 250° F. A formate compound is not required to achieve high-temperature stability in the fluid. Thus, the fluid is less expensive than conventional polymer-containing aqueous wellbore treatment fluids. The aqueous fluid may serve as, for example, a drilling fluid in the wellbore and thus may be circulated through the wellbore without being concerned that it could become unstable due to exposure to relatively high downhole temperatures.

Abstract: Methods of improving the thermal stability of an aqueous wellbore treatment fluid are provided. The wellbore treatment fluid comprises at least one polysaccharide and an effective amount of at least one polyacrylamide to maintain its stability at a temperature greater than about 250° F. A formate compound is not required to achieve high-temperature stability in the fluid. Thus, the fluid is less expensive than conventional polymer-containing aqueous wellbore treatment fluids. The aqueous fluid may serve as, for example, a drilling fluid in the wellbore. It may be circulated through the wellbore without being concerned that it could become unstable due to exposure to relatively high downhole temperatures.