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.