A chemical used to bind metal ions to form a ring structure. Chelating agents stabilize or prevent the precipitation of damaging compounds. In the oil field, chelating agents are used in stimulation treatments and for cleaning surface facilities. They are also used to treat or remove scale or weighting agents in reservoir drilling fluids.
During acid or scale-removal treatments, various compounds may be dissolved in the treatment fluid. As the acid reacts and the pH increases, reaction products may precipitate as a gelatinous, insoluble mass. Should this occur within the formation matrix, it is almost impossible to remove and permanent permeability damage may occur. Chelating agents prevent precipitation by keeping ions in a soluble form until the treatment fluid can be flowed back from the formation during cleanup.
Typical oilfield chelating agents include EDTA (ethylenediamine tetraacetic acid), HEDTA (hydroxyethylenediamine triacetic acid), NTA (nitriolotriacetic acid) and citric acid.