Carbon dioxide (CO2) is corrosive as a wet gas, dissolved gas in brines, or as a supercritical fluid with contaminants. Subsurface equipment made of nickel-based alloys has become well-established in hydrocarbon production; CO2 sequestration demands for identical alloys, despite the availability of potentially suitable stainless steels. In this paper, the author discusses results from complementary corrosion tests on metallic materials from tubular products and well equipment, including subsurface safety valves. The test program exposed corrosion-resistant alloys (i.e.,13Cr,15Cr, 17Cr, 22Cr, 25Cr, 925, 718, 716) to supercritical and near-supercritical fluids (dense phases) with elevated contaminant levels [i.e., water (H2O), oxygen (O2), hydrogen sulfide (H2S), sulfur oxide (SOx), nitrogen oxide (NOx), hydrogen (H2)] in addition to chloride-rich brines. The testing consisted of 4,000-to-4,500 psi (276-to-310 bar) autoclave tests at 70°F (21°C), 175°F (79°C), and 425°F (219°C), with test samples of each alloy immersed in the CO2-rich lighter fluids and the chloride brines. The materials were evaluated for mass loss, pitting, and crevice corrosion under pH values between 2.5 and 3.4. Overall, Alloy 718 was identified as a fairly complete alloy for CCS well equipment, while Alloys 25Cr and 925 continue to be attractive. For low temperatures and low contaminant levels, Alloys 17Cr and 22Cr can remain acceptable on a case basis, but are not recommended for typical subsurface equipment, because tubing metallurgy overmatching and manufacturing considerations weight heavily in favor of the nickel-based alloys.

Subject
Water, Materials, Corrosion resistant alloys, Stainless alloys, Corrosion rate, Nickel based alloys, Molybdenum alloys, Sour environments, Fluids, Equipment, Brines, Stainless steel, Alloys
Keywords:
carbon dioxide, corrosion-resistant alloys, impurities, uniform corrosion, pitting corrosion, materials selection, well completion equipment
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2023
Association for Materials Protection and Performance (AMPP)
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