Corrosion Rates of Cr- and Ni-Based Alloys With Organic Acids and Chelating Agents Used in Stimulation of Deep Wells

Abstract

SummaryAcid treatments of deep wells completed by use of chromium (Cr) -based tubulars represent a real challenge to the oil industry. On one hand, Cr-based tubulars are used to protect against carbon dioxide (CO2) corrosion, but on the other hand, the protective layer [chromium(III) oxide (Cr2O3)] dissolves in hydrochloric acid (HCl). This makes protection of Cr tubulars during acidizing very challenging, especially at high temperatures. At temperatures greater than 200°F, there is a need to add corrosion-inhibitor intensifiers, most of which depend on heavy metals [copper (Cu) or antimony (Sb)] or are not effective at temperatures greater than 300°F [e.g., potassium iodide (KI)].Over the last decade, a new chelant was developed, glutamic acid N, N-diacetic acid (GLDA), which can dissolve carbonate minerals from both carbonate and sandstone formations. This chelant can form wormholes in carbonates (both calcite and dolomite) and does not destabilize clay particles present in sandstone formations. In the present paper, the corrosion rate of GLDA solutions is compared with that of other chelants and simple organic acids that are used for carbonate dissolution, such as hydroxyethylethylenediaminetriacetic acid (HEDTA), acetic acid, and formic acid. All corrosion tests were conducted at high temperatures and pressures and extended for up to 6 hours at temperature and pressure. The Cr and nickel (Ni) -based coupons representing tubular metallurgy were examined thoroughly after the tests, and the spent fluids were analyzed for key cations [Cr, Ni, molybdenum (Mo), iron (Fe), and manganese (Mn)].Compared with formic acid, acetic acid, and even HEDTA, GLDA is much less corrosive to Cr-13 alloys. The results of this work show that GLDA at 20 wt% causes almost no corrosion with Cr-13 up to 300°F. Unlike GLDA, HEDTA was found to be corrosive at a pH = 3.8, and requires attention when used in wells completed with Cr-13-based tubulars. On more-corrosion-resistant Cr- or Cr-Ni-based alloys, such as super Cr-13, Duplex-2205, Inconel-625, and Incoloy-925, the corrosion rate of GLDA is still far below the acceptable limit of 0.02 to 0.05 lbm/ft2 up to 350°F. In wells with corrosive sweet and sour gases, tubulars consisting of low-carbon steel, Cr-based steel, or corrosion-resistant Cr-Ni alloys can be effectively protected by a combination of GLDA with a minimal amount of a suitable corrosion inhibitor. Because of its favorable environmental profile, this mixture meets all the Oslo-Paris Convention for the Protection of the Marine Environment of the Northeast Atlantic (OSPAR) requirements for use in the North Sea. On the basis of these results, GLDA solutions can be used to stimulate carbonate and sandstone wells completed with Cr- and Ni-based tubulars, while maintaining the integrity of the tubulars.