Iron precipitation has been recognized as a significant problem in acidizing operations for over 30 years. Deposits of iron compounds in tubulars combined with iron compounds in the formation determine the amount of iron dissolved by the acid and therefore, the severity of the iron problem. Data from the analysis of recovered acid on previous jobs canbe used to predict the concentration of iron that may need to be sequestered on future jobs.

Iron sequestering additives may present compatibility problems. Specific types of compatibility problems may be encountered when acidizing limestone formations with HCl, while other compatibility problems may be encountered when acidizing sandstone formation with HC1-HF blends.

Iron sequestering additives may lose effectiveness because of degradation. Degradation properties of less stable additives are discussed. The iron sequestering additives currently used are described and their effectiveness is compared using laboratory test data.

Iron sequestering in the presence of sulfides present unique problems which are explained. A system for sequestering iron in the presence of sulfides is described. Job descriptions and results from acidizing operations are presented.

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