Many high temperature sour gas wells, world-wide, have accumulated heavy iron sulfide deposit on downhole tubulars and in surface flowlines near wellheads. The scale deposits decrease well productivity, restrict well intervention, and interfere with downhole surveillance. Efficacious scale removal has become an important part of field operation for the reliable, efficient, and safe recovery of condensate-rich natural gas from these prolific wells.
Mechanical methods, such as milling, jetting, or a combination of both, are currently used for downhole remedial descaling. Meanwhile, many efforts have been devoted in recent years to identify and develop satisfactory scale dissolvers with the aim of reducing operation cost and enhancing cleaning efficiency. This paper summarizes the latest developments in iron sulfide dissolver studies. Laboratory tests were performed to evaluate some newly developed products for thermal stability, corrosivity to mild steel, compatibility with formation water, and dissolving capacity to authigenic mineral and field deposits at different temperatures. It is hoped that this paper will not only serve as a useful summary of recent advancements, but also clearly illustrate the remaining challenges, which need to be addressed.
Key words: Iron sulfide, oilfield scale, scale dissolver, THPS, HCl, pyrrhotite, pyrite, marcasite