Thermal stabilizer for non-clay wellbore fluids

In the method of drilling, workover or completion of oil and gas wells using an aqueous polysaccharide solution non-clay well bore fluid, said polysaccharide being a viscosifier and selected from the class consisting of hydroxyalkyl cellulose having 2 to 4 carbons in the alkyl, carboxymethyl hydroxyethyl cellulose, hydroxyalkylated guar gum, xanthan gum or hydroxyethyl carboxyethyl cellulose wherein said wellbore fluid is injected into the wells in contact with the formation, the improvement which comprises incorporating into said solution about 0.5 to about 13% by weight of calcined dolomite, based on the weight of polysaccharide.