Iron sulfide scale can be relatively common-place in maturing oil wells and produced water handling systems. Iron sulfide can also be commonly formed as a corrosion product, due to sour corrosion resulting from H2S containing fluids being processed through carbon steel tubulars. As more sour production is brought on-stream iron sulfide continues to become more prevalent. There are few options for removing deposits of iron sulfide scales especially when it comes to choice of chemistry. This paper discusses the most commonly performed techniques for iron sulfide removal, including hydrochloric acid, organic acids and THPS, and the varying degrees of success that these chemistries have in application. Challenges using hydrochloric acid are encountered due to the potentially high yield of H2S upon dissolution of the scale, along with FeCl2 and therefore the potential of secondary deposition.
This paper provides data on the development of a new dissolver for iron sulfide. Dissolver tests were performed initially on laboratory generated iron sulfide scale to optimize the formulation. Further testing was performed on different polymorphs of iron sulfide including pyrite, pyrrhotite, troilite, marcasite and mackinawite. Furthermore, several field scales were obtained and after XRD analysis, tested with the novel dissolver chemistry. It was shown that the new chemistry significantly outperformed THPS based dissolvers (active for active) and as well as 7.5% HCl. The corrosion rate of the novel chemistry was significantly lower than inhibited HCl and commercial THPS based blends. Testing was also performed at high pressure in order to understand the influence that pressure has on dissolution rates for all the commonly used dissolver chemicals. The new dissolver chemistry has significant chelating ability for sulfide scales as well as other ‘standard’ scale types including, calcium carbonate and calcium sulfate. The new product offers an effective multi-functional solution to dissolution of heterogeneous scale deposits.
The paper concludes with a case history of field application summarizing in detail the parameters of the field deployment and various KPIs used to measure success. The application is unusual as it was performed using a continuous injection method into an online system.