1. n. [Well Workover and Intervention, Well Completions]

Also known as a chelating agent, a chemical added to an acid to stabilize iron. In the oil field, acid is used in stimulation treatments and to treat or remove scale or weighting material in reservoir drilling fluids.The injected acid dissolves iron from rust, millscale, iron scales or iron-containing minerals in the formation. Iron can exist as ferric iron [Fe⁺³] or ferrous iron [Fe⁺²]. If the iron is not controlled, it will precipitate insoluble products such as ferric hydroxide and, in sour environments, ferrous sulfide [FeS], which will damage the formation. Chelating agents associate with iron [Fe⁺³ or Fe⁺²] to form soluble complexes. Citric acid, acetic acid and EDTA are effective chelating agents and can be used at temperatures up to 400^oF [204^oC].

See: reducing agent