Tetrakis(hydroxymethyl)phosphonium sulfate (THPS), regarded as one of the most effective oilfield biocides in fighting SRB, is also found being able to dissolve iron sulfide scales which are known difficult to be solubilized. In this work the dissolution behavior of THPS on zinc sulfide and lead sulfide scales was studied. A combination of THPS up to 30 wt.% with ammonium chloride up to 12 wt.% is effective to zinc and lead sulfide scales. The THPS showed limited dissolution behaviour with all

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... ther additives which contain ammonium ion or chloride ion alone, which suggests that ammonium chloride is a critical ingredient of the dissolution process. The phosphonates additives also showed no dissolution behavior. The dissolution reaction is temperature and time dependent as the maximum dissolution was obtained at 85°C and after 24 hours. The corrosivity of the proposed mixture was generally less than that of the inhibited acid solutions.