Acid treatments of deep wells completed with Cr-based tubulars represent a real challenge to the oil industry. On one hand, Cr-based tubulars are used to protect against CO2 corrosion, but on the other hand, the protective layer (Cr2O3) dissolves in hydrochloric acid (HCl)- a common stimulation fluid. This fact makes protection of Cr tubulars during acidizing very challenging, especially at high temperatures. At temperatures above 200°F, there is a need to add an intensifier. Most of them depend on heavy elements (Cu, Sb), or are not effective above 300°F (e.g., KI).
Over the last decade, we developed a new chelate, glutamic acid N, N-diacetic acid (GLDA) that can dissolve carbonate minerals from carbonate and sandstone formations. This chelate can form worm holes in carbonates (both calcite and dolomite) and does not destabilize clay particles. In the present paper, the corrosion rate of GLDA is compared with other chelates and simple organic acids that are used for carbonate dissolution, such as hydroxyethylethylenediaminetriacetic acid (HEDTA), acetic and formic acid. All corrosion tests were conducted at high temperatures and pressures and extended for up to 6 hour at temperature and pressure. The coupons were examined thoroughly after the tests, and the spent fluid was analyzed for key ions (Cr, Ni, Mo, Fe, and Mn).
The results show that GLDA at 20 wt% gives almost no corrosion with Cr-13 up to 300°F. Unlike GLDA, HEDTA was found to be corrosive at pH=3.8 and requires attention when used in wells completed with Cr-13 based tubulars. On more corrosion resistant Cr-based metals, like super Cr-13 and Duplex the corrosion rate of GLDA is still far below the acceptable limit of 0.02 to 0.05 lbs/ft2 up to 350°F. In wells with corrosive sweet and sour gases tubular 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 corrosion inhibitor. Due to its favorable environmental profile this mixture meets all the OSPAR requirements for use in the North Sea. Based on our results, GLDA solutions can be used to stimulate carbonate and sandstone wells completed with Cr-based tubulars, while maintaining the integrity of the tubulars.