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Abstract

Various water-soluble additives, either alone or in various combinations, for use in water-based clay drilling fluids. The additives are an acrylate polymer, an acrylate propylene glycol copolymer and three structurally different sulfonate amide polymers. One of the sulfonate amide polymers is a terpolymer consisting of a random distribution of units of the formulae ##STR1## wherein R.sub.1 and R.sub.2 are the same or different and each is hydrogen, methyl, or ethyl, and X.sup.+ is a cation. A second sulfonate amide polymer is a copolymer consisting only of a random distribution of units (a) and (b). The third sulfonate amide polymer is a copolymer consisting of 2-acrylamido-2-methyl propane sulfonic acid and acrylamide. The acrylate polymer is of the formula ##STR2## while the acrylate propylene glycol copolymer is of the formula ##STR3## Drilling operations using a drilling fluid containing these compositions can be carried out at pH levels from about 8 to 11.5 and at temperatures up to about 220.degree. C. The use of the above compositions in a water-based clay drilling fluid results in a reduced fluid loss rate.

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