Prevention of sulfide scale through the use of chemistry is a developing area of focus within the oil industry. There are few examples of a single chemical approach working, where scale inhibitor species function at threshold concentrations. Partial inhibition may be provided by ‘standard’ scale inhibitors using established chemistries such as phosphonates or polymeric species. However, the efficacy of these inhibitors against sulfide scale is generally poor and high concentrations are typically required.

Based on an industry need for a true, high-performance sulfide scale inhibitor, work was undertaken to develop a novel chemistry that would offer a step-change in performance from existing technologies. Using a new advanced rapid screening technique, a wide range of ‘standard’ scale inhibitors were assessed, which proved that the majority of these chemistries display no efficacy against sulfide scale. A select few of the standard scale inhibitors displayed limited efficacy and from this data common molecular features which contributed to sulfide scale inhibition were identified.

Utilizing this knowledge, a range of novel polymeric chemistries were synthesized which provide significantly superior inhibition than any other postulated for this application. It has been possible to identify specific moieties within these complex polymers which are required for sulfide scale inhibition and to theorize on likely molecular structure-performance relationships for this new class of scale inhibitor. Additionally, hypotheses on the specific mechanisms by which these inhibitors function have been provided, showing why they are so successful at sulfide crystal growth retardation.

Static and dynamic test methods are described that accurately mimic formation of these scales in the field, in comparing the novel polymeric chemistry with the best-performing ‘standard’ scale inhibitors. Order of magnitude increases in performance over standard species are reported which represents a true step-change in the efficacy of sulfide scale inhibition.

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