Review of Iron Sulfide Scale Removal and Inhibition in Oil and Gas Wells: Current Status and Perspectives

Iron sulfide scale is one of the main types of inorganic scales that block oil and gas wells. Iron sulfide has polymorph crystallinity structures, which complicate its dissolving and inhibition. Hydrochloric acid (HCl) is used conventionally to remove iron sulfide scale; however, toxic hydrogen sulfide (H2S) is released. Consequently, tubular corrosion and formation damage are accelerated. This review highlights the major role of understanding iron sulfide chemistry in developing chemicals for removing or inhibiting the different iron sulfide polymorphs. Furthermore, the physical features of iron sulfide types and the optimum conditions for their formation in terms of depth, temperature, pressure, and well types are explored. The article also emphasizes the mechanisms and introduces the new green formulations used to dissolve and inhibit iron sulfide. Moreover, recent theoretical work on molecular simulation efforts proved to be significant in identifying potential dissolvers and inhibitors and insightful on the reaction mechanisms. Furthermore, the field practice in removing this type of scale is illustrated with field case studies to present the obstacles facing the efficient implementation of the lab-scale techniques. Finally, the environmental impact and economic assessment are reviewed to identify the most efficient chemicals.