Iron Sulfide Removal: A Nonacidic Alternative to Hydrochloric Acid Treatment

Abstract

Iron sulfide scale deposition is a common problem in sour oil and gas wells. Accumulation of iron sulfide in the production tubing causes reduction of well deliverability. Conventional chemical means to remove Iron sulfide scale usually involve hydrochloric acid and other mineral acids. The composition and crystalline structure of iron sulfide scales varies significantly. Although iron disulfide (FeS 2 ), which is found in the minerals such as marcasite and pyrite, is not soluble in acid, pyrrhotite (Fe 7 S 8 ) has a high solubility in hydrochloric acid. Therefore, although hydrochloric acid and other acids can be applied to remove iron sulfide scales, their effectiveness in different treatments could be quite different depending on the scale composition. Even in cases where hydrochloric acid could be applied for iron sulfide removal, the applied hydrochloric acid is very corrosive to downhole tubulars especially at high temperatures and high acid concentrations. In the meantime, the generated H 2 S poses a great threat because of its high toxicity and enhanced corrosion tendency due to the combination of hydrochloride acid and H 2 S.To overcome the drawbacks of hydrochloric acid treatment, i.e., the risk of H 2 S evolution and the corrosion tendency in standard carbon steel, an alternative chemical treatment to hydrochloric acid treatment is preferred. This paper illustrates the development of a new chemical treatment solution for iron sulfide removal. This polymer-based system demonstrated high dissolving capacity for iron sulfide scales in neutral or nearly neutral pH environments. Testing related to its performance also has revealed advantages such as low corrosion rate, and low H 2 S evolution. Additionally, laboratory testing demonstrated this polymer-based system is an effective general purpose stimulation fluid to stimulate carbonate and dolomite formations. IntroductionIt has been well documented that iron sulfide scales can cause various problems in the oil industry. Iron sulfide scale precipitation in the formation matrix and around screens and perforations can decrease production capacity. Accumulation of iron sulfide scale in the tubulars can result in reduced well deliverability. The build-up of iron sulfide scale could also interfere with the operation of pumps, valves and other associated equipment. Downhole blockages also slow the flow of fluids thereby creating flow assurance issues. Since the surface of iron sulfide is oil-wet, the free-floating iron sulfide particles are often found at the oil-water interface to stabilize emulsions and interfere with the separation process

Barium Sulfate Scale Removal at Low-Temperature

“…Therefore, specific chemical additions need to be added to control these impacts during the scale removal jobs [5,[36][37][38]. In addition to that, the performance of HCl was found efficient in specific scale types as zinc sulfides [39], pyrrhotite, and troilite of iron sulfides. However, the results did not show great solubility with sulfate scales as strontium, calcium, and barium [20,21].…”

Applications of Chelating Agents in the Upstream Oil and Gas Industry: A Review

“…However, there are several disadvantages associated with HCl that limit the application of HCl. For example, the use of HCl at a high-temperature condition is very challenging and expensive as a result of the requirement of additional additives to control the reaction rate . Some iron sulfide scales, such as pyrite, have very low solubility in HCl .…”

A Novel Low-Temperature Non-Corrosive Sulfate/Sulfide Scale Dissolver

“…However, using HCl for scale removal cannot dissolve many scale types, expensive, corrosive, and generates toxic gas H 2 S and therefore other additives must be added to control the reaction [5,[29][30][31]. HCl can dissolve zinc sulfide [32], and few iron sulfide scales as troilite and pyrrhotite; however, pyrite and marcasite are difficult to dissolve with HCl [31]. Sulfate scales such as barium, calcium, and strontium sulfates were found to have low HCl acid-solubility [22,33].…”