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.degree. 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.

 
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< Use of a polyster composition as a hydraulic fluid

> Dispersions stabilized at temperatures of from 4 to 50 degrees celsius by means of a polymer comprising water-soluble units and units with an LCST

> Method for treating aqueous sludge, material so produced and the use thereof

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