Abstract
Pyrite scale formation is a critical problem in the hydrocarbon production industry; it affects the flow of hydrocarbon within the reservoir and the surface facilities. Treatments with inorganic acids, such as HCl, results in generation toxic hydrogen sulfide, high corrosion rates, and low dissolving power. In this work, the dissolution of pyrite scale is enhanced by the introduction of electrical current to aid the chemical dissolution. The electrolytes used in this study are chemical formulations mainly composed of diethylenetriamine-pentaacetic acid–potassium (DTPAK5) with potassium carbonate; diethylenetriamine pentaacetic acid sodium-based (DTPANa5), and l-glutamic acid-N, N-diacetic acid (GLDA). DTPA and GLDA have shown some ability to dissolve iron sulfide without generating hydrogen sulfide. The effect of these chemical formulations, disc rotational rate and current density on the electro-assisted dissolution of pyrite are investigated using Galvanostatic experiments at room temperature. The total iron dissolved of pyrite using the electrochemical process is more than 400 times higher than the chemical dissolution using the same chelating agent-based formulation and under the same conditions. The dissolution rate increased by 12-folds with the increase of current density from 5 to 50 mA/cm2. Acid and neutral formulations had better dissolution capacities than basic ones. In addition, doubling the rotational rate did not yield a significant increase in electro-assisted pyrite scale dissolution. XPS analysis confirmed the electrochemical dissolution is mainly due to oxidation of Fe2+ on pyrite surface lattice to Fe3+. The results obtained in this study suggest that electro-assisted dissolution is a promising technique for scale removal.
Highlights
Pyrite scale formation is a critical problem in the hydrocarbon production industry; it affects the flow of hydrocarbon within the reservoir and the surface facilities
Chemical methods, which include the use of chelating agents, have proved useful in removing iron sulfide scales which have about equal ratio of iron to sulfur atoms such as pyrrhotite ( Fe7S8) and troilite (FeS)[7,8,9]
The chemical and the electrochemical dissolution was performed in the system of rotating disk electrode (RDE) and Potentiostat
Summary
Pyrite scale formation is a critical problem in the hydrocarbon production industry; it affects the flow of hydrocarbon within the reservoir and the surface facilities. DTPA and GLDA have shown some ability to dissolve iron sulfide without generating hydrogen sulfide The effect of these chemical formulations, disc rotational rate and current density on the electro-assisted dissolution of pyrite are investigated using Galvanostatic experiments at room temperature. Besides the mining industry, pyrite causes another problem in the oil and gas industry as it forms scales in reservoirs These scale deposits hinder the flow assurance near-wellbore area of the reservoir, which leads to blockage of the downhole tubular, formation damage, and complete shutdown of production and operational processes. Both mechanical and chemical methods were applied in resolving the problems created by pyrite scales. Iron ions redox reactions have been studied recently by Li et al.[4,15]
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