Abstract: A method for inhibiting barium sulfate precipitation in low pH aqueous fluids of underground petroleum-bearing formations by adding to such systems an effective amount of low molecular weight water-soluble polymer containing 5-35 weight percent sulfonic acid monomer units and 65-95 weight percent carboxylic acid monomer units, is provided. Polymer compositions based on 10-15 weight percent 2-acrylamido-2-methyl-1-propanesulfonic acid, 15-65 weight percent acrylic acid and 25-70 weight percent maleic acid are particularly preferred for use at very low pH conditions, e.g., 5.5 or less in the presence of high sulfate ion and barium ion concentrations.

Abstract: The present invention provides a method for inhibiting the formation of metal sulfate scale in an aqueous system. Metal sulfate scale formation is inhibited by adding an effective amount of one or more poly(amino acids) and one or more inorganic phosphates to the aqueous system. The poly(amino acids) are a reaction product formed from at least one compound selected from amino acids, amic acids, ammonium salts of monoethylenically unsaturated dicarboxylic acids, and ammonium salts of hydroxypolycarboxylic acids. The present invention also provides a method of inhibiting the formation of metal sulfate scale by adding an effective amount of a poly(amino acid) which contains tyrosine, tryptophan, histidine, arginine or combinations thereof.