Abstract: A low viscosity drilling fluid and method for stabilizing a downhole shale formation are disclosed. The fluid comprises an aqueous solution of a partialy transamidated hydrolyzed acrylamide copolymer, potassium chloride, a weighting agent and an optional viscosifying agent. The copolymer comprises from about 50 to about 98 mole percent primary amide functionality, from about 0.1 to about 15 mole percent secondary amide functionality and from about 2 to about 50 mole percent of the acrylate salt. The drilling fluid has a density out from about 8 to about 18 pounds per gallon and a viscosity of from about 5 to about 30 centistokes.

Abstract: A precipitation control composition comprises an iron sequestering agent and a ketone-type compound as sulfide modifier. The precipitation control composition is useful to retard undesirable precipitation of iron and sulfur species from an acid solution of increasing pH. In combination with an acid solution, the precipitate control composition comprises an acidizing composition which is particularly useful in the acidizing of sour hydrocarbon wells. Also disclosed is the method of retarding undesirable precipitation of iron and sulfur species from an acid solution of increasing pH.