Carbon dioxide capture, utilization, and storage (CCUS) is part of decarbonization solutions to reduce green-house gas emissions, as exemplified by the growing number of capital expenditure projects worldwide.1-2 In CCUS, the carbon dioxide (CO2) is consecutively (1) captured at origin, such as power plants and natural gas production sites, (2) separated from other gases and impurities, (3) compressed, (4) transported through pipelines, and finally (5) injected into a storage site such as deleted hydrocarbon wells, saline aquafers, coal beds, underground caverns, or seawater.1,3 Since the 1970s, specifically the first commercial carbon dioxide flooding in the United States (known as SACROC), carbon dioxide sequestration has been largely discussed in the context of enhanced oil recovery (EOR), not in the newer context of Sustainability. Nonetheless, substantial experience has been drawn from EOR, including for the selection of the right and economical materials.4 As reflected by the literature, past materials test programs have rarely given any attention to downhole jewelry alloys compared to tubulars or surface-infrastructure alloys, and consequently the track records for such bar-stock alloys are either inexistent or not readily available. 5-7 This lack of apparent return-on-experience represents a knowledge gap against the prospect of a safe greenhouse gas control method; needless to say, it also justifies the requirements for reliable well integrity monitoring solutions in carbon dioxide sequestration wells.8-9
Product Number:
51322-17882-SG
Author:
Manuel Marya
Publication Date:
2022
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Corrosion-Resistant Alloys (CRAs), among commercial Ni/Fe-Cr-Mo alloys for surface, subsea, and downhole equipment, and among traditional and proprietary cast Fe-Ni-Cr alloys for pressure pumping operations have been corrosion evaluated and ranked for their environmental resistance in two static carbon-dioxide environments with liquid brines in equilibrium. The selected CRAs were tested not only in their API Spec 6ACRA heat-treated conditions, but also after liquid nitriding, with specific attention given towards general, pitting, and crevice corrosion. All environmental tests were completed over a 30-day period in 4000psi (276bars) pressurized autoclaves at a temperature of 425°F (218°C) with either oxygen (0.5% O2) or sour gas (20% H2S). The tested CRAs were exposed to both a denser 90,000-120,000ppm NaCl-rich liquid brine, purposely supersaturated with oxygen or sour gas, and a lighter and supercritical carbon dioxide fluid containing water along with oxygen or hydrogen sulfide. For the two selected environments, the test results have revealed the following: (1) corrosion in liquid brines and supercritical fluids turned out to be comparable and rarely alarming, (2) all tested Ni/Fe-CrMo wrought alloys corroded less than the cast alloys; i.e., ~0.5 to ~1.1mpy (~12 to ~28m), (3) nitriding, while generally inconsequential to the Ni/Fe-Cr-Mo alloys, produced thin layers that corroded faster and delaminated, (4) the novel cast alloys, having a general corrosion resistance closer to the wrought NiCr-Mo alloys, outperformed the traditional pump cast alloys; i.e., ~4.0 to ~40mpy (~0.1 to ~1.0mm), (5), general corrosion and pitting were the dominant corrosion mechanisms with (6) oxygen accelerating corrosion more than hydrogen sulfide. For the nitrided alloys, the progressive chemical conversion of the nitrided layer into a delaminating corrosion byproduct is proven to occur rapidly, resulting in the exposure of the base materials without noticeable accelerated corrosion over equipment lifespan.
