Tetrakis(hydroxymethyl)phosphonium Sulfate (THPS), an environmental friendly biocide, is gaining more interest as a dissolver to control iron sulfide (FeS) precipitation in oilfield production systems. In previous works, combinations of THPS and different additives, such as ammonium chloride, chelating agents or organic phosphonates, were examined for the synergistic effects of FeS scale dissolution under room and high temperatures. It was found that THPS and ammonium ion can create a purple-colored complex which can significantly improve the FeS dissolution. Studies also indicated that the synergistic effect of ammonium chloride was largely attributed to pH decrease. As a result, the corrosivity of THPS solution to metallurgy was increased. In this work, new formulations based on THPS is introduced. Chloride ions were substituted with different organic compounds. The dissolution rate of analytical grade FeS solid and carbon steel corrosion were investigated at different temperatures. The chemical composition of the undissolved FeS solid and the THPS-Amine-Iron complex structure were analyzed for the most effective dissolver formulations. The efficiency of new formulations was further evaluated using field scale samples collected from water injection pipeline and a sour gas well, and the structures of the FeS scale before and after dissolver treatment were studied to reveal the mechanism of dissolution.

Keywords:
Hydrate Remediation, hydrate inhibition, asphaltene inhibition, wax remediation, oilfield chemistry, scale inhibition, paraffin remediation, wax inhibition, asphaltene remediation, scale remediation
Subjects:
Production Chemistry, Metallurgy and Biology, Pipelines, Flowlines and Risers, Inhibition and remediation of hydrates, scale, paraffin / wax and asphaltene, Materials and corrosion
Copyright 2018, Society of Petroleum Engineers
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