Abstract
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. There have been commercially available dispersants for iron sulfide scale particles, but can transfer iron sulfide scale to the oil phase, causing another issue during oil and gas operational activities. In this study, stability of FeS particles produced in a strictly anoxic condition were examined with several different water-soluble polymers in various reaction conditions. Among tested water-soluble polymers, polyacrylamide, polyvinyl pyrrolidone, oxazoline and carboxymethyl cellulose successfully prevented FeS particles from settling in the conditions of Ca2+ concentrations as high as 200 mM at both pHs of 5.0 and 6.7 with the polymer concentrations as low as 20 mg/L. The size of FeS stabilized in polymers remained in nano-scale. Polymers did not work as threshold inhibitors, but prevented particle growth. Polymers changed FeS wettability from oil-wet to water-wet.
