Objectives the scale problem related to the formation of iron sulfide is commonly found during oil and gas productions in sour environments using low corrosion resistant carbon steel equipment and pipes. When hydrogen sulfide gas is evolved resulting from sulfate reducing bacteria or thermal decomposition of sulfate in the presence of iron from various corrosion processes in downhole iron sulfide can quickly precipitate. Although iron sulfide scale is not as common as carbonate and sulfate scales it is difficult to inhibit especially at high temperature conditions due to its low solubility and fast precipitation kinetics. Because efficient inhibitors for iron sulfide scale have not been found the application of iron sulfide dispersants could be an alternatively feasible method to control iron sulfide scale problems. There have been commercially available dispersants for iron sulfide scale particles but can transfer iron sulfide scale to the oil phase causing another issues during oil and gas operational activities. In this study we identify efficient and effective inhibitors/dispersants for iron sulfide scale while maintaining iron sulfide in the water phase as well as preventing iron sulfide from transforming to more stable and insoluble forms. We also investigate different operational and solution conditions and characterize iron sulfide solids using instrumental analytical techniques to understand scale controlling reaction mechanism.MethodsMore than 50 different chemical formulations are investigated for iron sulfide scale inhibition or dispersion in a batch reactor system under a strictly anoxic environment. To produce an anoxic environment we prepare all solutions in air-tight apparatus while sparging ultra-high purity grade argon gas (DO < 5 ppb). Reactions are carried out in temperature controlled glass reactors. Different operational and solution conditions are tested such as pH temperature ionic strength inhibitor concentrations and iron sulfide saturation index. Iron sulfide solids are characterized using SEM TEM DLS XRD and FT-IR and ferrous iron and sulfide concentrations in filtered solutions are analyzed using colorimetric methods with UV-VIS spectrophotometer.ResultsOur studies indicate that biocides such as tetrakis (hydroxymethyl) phosphonium chloride may not be effective inhibitors for iron sulfide scale. Amide-group containing polymeric compounds show a promising effect on dispersing iron sulfide particles in water phase rather than dissolving them as with ethylenediaminetetraacetic acid. Other biodegradable and non-toxic polymer groups commonly used for nanoparticle stabilization for biomedical applications are also tested to disperse iron sulfide particles and demonstrate great dispersibility of iron sulfide in water. SEM analysis shows that polymer dispersed iron sulfides remain in amorphous iron sulfide unlike one without polymers which is transformed to gregite or pyrite after aged for 10 days at 75 ◦C. Characterizations of water soluble polymers dispersing iron sulfide and iron sulfides dispersed in polymers are ongoing. The operational and solution conditions for dispersing iron sulfide in polymer are also currently being investigated. Novel implicationsIron sulfide such as mackinawite has been reported as a corrosion product of steel pipes. Iron sulfide scale is hard to control due to fast precipitation kinetics and extremely low solubility. Commercial scale inhibitors do not effectively inhibit nucleation of iron sulfide solid and dispersants available on the market can often transfer iron sulfide particles to the oil phase causing an additional issue during oil and gas production activities. Moreover initially formed unstable amorphous iron sulfide could be transformed to stable form which is much more difficult to control. The our results of identifying iron sulfide dispersants to solve all issues mentioned previously and understanding of the mechanistic function of polymeric dispersants to optimize the processes would of great alleviate iron sulfide scale problem resulting in technical and financial benefits.