Drilling fluid containing caesium compounds

摘要

The present invention relates to a drilling fluid having a specific gravity of between 1.2 g/cm 3 and 2.5 g/cm 3 and comprising an aqueous mixture on a dry salt basis of between 10% and 100% of a cesium salt, said drilling fluid comprising on a dry salt basis less than 0.50% by weight of chloride or sulfate anions; less than 0.3% by weight of materials selected from Al, Ba, Ca and Mg; and less than 0.2% by weight in total of other multivalent cationic impurities; and said cesium salt being obtainable by a process comprising the steps of
(a) treating cesium alum with slaked lime or calcium carbonate and an acid or a salt of said acid to produce a cesium salt of said acid and an undissolved solid comprising aluminum hydroxide, wherein said cesium salt includes calcium ions and sulfate ions as impurities;
(b) separating the solubilized cesium salt solution from the undissolved solid; and
(c) adding barium hydroxide to the solution of said cesium salt containing said impurities in an amount sufficient to precipitate sulfate ions to provide said cesium salt with less than 1000 ppm of sulfate ion.