Abstract: A clay-free wellbore fluid having thixotropic properties, good surface handling characteristics and excellent subterranean characteristics such as particle handling gel strength, and low water loss has been devised by the combination of a heteropolysaccharide prepared by the action of bacteria of the genus Xanthomonas on carbohydrates, modified starch and MgO. In some situations a salt of lignosulfonate is added to maintain the desirable properties of the wellbore fluid.

Abstract: A clay-free, i.e., non-argillaceous brine wellbore fluid having unstructured viscosity and improved water loss properties from an additive composition present in an amount of 0.1 to 3 weight % based on wellbore fluid and consisting essentially of 15 to 95 weight % of guar gum or hydroxyalkyl guar gum and 5 to 85 weight % of a water soluble salt, preferably alkaline earth salt of lignosulfonate.

Abstract: Lost circulation in a well occurring during drilling is reduced by aeration of clay-free, non-thixotropic, brine wellbore fluids comprising hydroxyalkyl cellulose and preferably magnesia as a stabilizer. The gas is easily and completely removed from the foam returned to surface with only a conventional degassing and gas busting equipment normally found in a solids removal system. The advantages of the clay-free, non-thixotropic, drilling fluids as known are preserved and the system allows rapid change from aerated to non-aerated fluid as required.

Abstract: A clay-free, i.e., non-argillaceous wellbore fluid, having unstructured viscosity is obtained by combining water with an additive composition comprising guar gum and at least 10 weight percent of magnesia or magnesium hydroxide based on the weight of guar gum.

Abstract: A clay-free, i.e., non-argillaceous brine wellbore fluid having unstructured viscosity and improved water loss properties from an additive composition present in an amount of 0.1 to 3 weight % based on wellbore fluid and consisting essentially of 15 to 95 weight % of guar gum or hydroxyalkyl guar gum and 5 to 85 weight % of a water soluble salt, preferably alkaline earth salt of lignosulfonate.

Abstract: The basic fluid is water, oil or an oil-water mixture. The primary weighting materials are dissolved salts, e.g., sodium chloride, calcium chloride or mixed brines, and in these the calcium or sodium ions inhibit hydration and swelling of drilled solids. When non-cationic fluids are used, an inhibitor is added to prevent such hydration and disintegration--an electrolyte or a cationic surfactant. Any viscosifier added is one having neither a structured viscosity nor gel strength, hydroxyethyl cellulose, for example. When the drilling fluid is pumped to the surface, most of the drilled solids are in their original condition and size and are readily removed and discarded by screening and other available physical means. There is none of the build-up of solids associated with older systems and, hence, no need for discarding, thinning, and make-up.