Iron sulfide deposition is a significant oilfield problem that has been ignored for the most part because of the perceived difficulty in preventing its formation. Usually iron sulfide is allowed to form and the resulting deposit problem remediated by either acid treatment or mechanical cleaning. Neither option is attractive in that acid cleaning is hazardous and mechanical cleaning is expensive.
Iron sulfide is not a single entity, but can exist in numerous forms. This paper discusses the various forms of iron sulfide. It compares the solubilities of iron and other sulfides with the solubilities of other mineral scales typically found in the oilfield and shows that it should be possible to inhibit the formation of ferrous sulfides using threshold inhibitors.
The perceived difficulty of preventing the formation of iron sulfide arises primarily from the very real problems involved in studying it in the laboratory under the anaerobic conditions typically found in the oilfield. These problems and solutions to some of them are discussed. The paper presents laboratory and limited field data showing how the deposition of ferrous sulfides may be reduced significantly.