The Role of pH and Alkali Salts on Corrosion Indices of EDTA Solutions in Oilfield Applications

Chelating agents have wide usage in the oil and gas industry, and they are implemented in various processes including drilling, well stimulation, enhanced oil recovery, descaling, etc. With such heavy usage, it is critical to assess their potential to cause corrosion in well tubulars. In this work, EDTA solutions were prepared with three different salts, namely LiOH, NaOH, and KOH. Two preparation methods were implemented namely basification and acidification. In the basification method, the solution was prepared by increasing the salt concentration until specific pH values are reached (i.e., ~ 7 and ~ 12) while in the acidification method, the pH is lowered to 7 using HCl. The results showed that the basification line had the higher corrosion index in comparison with the acidification line while the lowest corrosion index was found at a pH of 12. The results revealed that EDTA-Li exhibited the lowest corrosion index among all tested salts, particularly at pH 12, suggesting its potential as a less aggressive chelating system. These findings were supported by ab initio calculations, the ab initio calculations which illustrated that the binding energy of the deprotonated EDTA with Li⁺ was higher in comparison with the Na⁺ and K⁺ cases. This reflected positively on the corrosion index, and the corrosion index was decreased in comparison with the Na⁺ and K⁺ cases.