Testing of OCTG Materials in Simulated CCS Environments: Comparing Different Approaches for Impurity Concentrations Definition

Abstract The underground injection of dense CO2 containing impurities for carbon capture and storage (CCS) applications poses potential risks to the integrity of downhole materials, particularly under conditions that may allow the presence of liquid brine. Testing materials for these environments remain challenging due to their complexity and the lack of standardized methodologies. Typically, materials are exposed to simulated CCS environments in autoclaves containing brine in contact with dense-phase CO2 being the incorporation of impurities one of the main challenges. This paper compares two approaches for the addition of impurities into the autoclave during experimental testing. In the first approach, impurities were added based on the nominal composition of the CO2 stream to be simulated. In this case, dissolution into the brine and chemical reactions among impurities will alter the actual composition of the CO2 phase. In the second approach, the amount of each impurity was adjusted to achieve target concentrations in the CO2 phase after accounting for solubility and dissociating reactions into the brine. Materials such as Martensitic Stainless Steels—known to be susceptible under the low pH conditions that can develop during CO2 injection with impurities—were evaluated under both scenarios. This paper describes the relative severity of each experimental approach and prompts further discussion on the need for standardized testing methodologies.

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