C.W. Crowe, Dowell Division of Dow Chemical
During the course of any acidizing treatment, a certain amount of iron is dissolved by action of the acid upon treating lines, equipment, downhole tubular goods and iron containing minerals present within the formation. Upon spending of the acid, this iron may precipitate as insoluble gelatinous ferric hydroxide. This precipitate is an effective plugging agent which damages permeability and restricts oil and gas production. In order to prevent iron precipitation, stabilizers are routinely added to the treating acid. These stabilizers form soluble chelates or complexes with iron and prevent precipitation of ferric hydroxide. This paper describes the advantages and limitations of the various commonly used iron stabilizing agents. Guidelines are presented for selecting the proper additive and determining the concentration needed for iron control. Well conditions, as they relate to the need for iron stabilizing agents, are also discussed.