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Abstract

A method of increasing the thermal stability of an aqueous wellbore fluid that includes a viscosifying agent, involves formulating the wellbore fluid so as to include an effective amount of a thermal stability compound selected from the group of gallic acid, gallow tannins, esters of gallic acid, salts of gallic acid and combinations of these compounds. The inclusion of the thermal stability agent surprisingly enhances the ability of the wellbore fluid to maintain viscosity and fluid loss properties upon exposure to high temperatures. Preferably the thermal stability agent is gallic acid or substantially pure 3,4,5-trihydroxybenzoic acid. The concentration of the thermal stability compound is from about 0.1% by weight to about 10% by weight of the wellbore fluid. The wellbore fluid is formulated to include a viscosifying agent such as starch, schleroglucans, guar gums, polyacrylates, xanthan gum, and combinations of these and similar compounds. Optionally, the wellbore fluid is formulated to include a weighting agent such as barite, hematite, iron oxide, calcium carbonate, alkali halides, alkaline earth halides, magnesium carbonate, zinc halides, zinc formats, zinc acetates, cesium halides, cesium formats, cesium acetates, and combinations of these and similar compounds.

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