ABSTRACT

Carbon capture, utilization, and storage (CCUS) is a set of promising technologies developed to meet global sustainable energy production and climate control goals. Among them, the application of supercritical CO2 captured from various industrial emitters for assisting enhanced oil recovery (EOR) is seen as an economic and efficient pathway. Because of their low cost and acceptable mechanical properties, low alloy steels are the primary materials of construction in s-CO2 EOR systems although they are highly susceptible to corrosion in wet s-CO2 environments, especially with the presence of excessive H2O and other aggressive impurities. This paper studied the corrosion of 2Cr steel in s-CO2 saturated aqueous environments with different impurities. The simulated s-CO2 environment was held at 8 MPa and 50 °C for 96 hours with 0.6 M (3.5 wt.%) NaCl in solution; in subsequent tests, 0.05 M of NaBr or Na2S impurities were added to partially replace NaCl to clarify the effects of other anions. Corrosion rates were determined using weight loss measurements. It was found that 2Cr steel showed the highest corrosion rate of about 2.0 mm/y in the Br-containing environment while its best performance occurred in the S-containing environment (around 1.4 mm/y). FeCO3 and chromium oxides were likely the main corrosion products formed in all environments. FeS and potentially Fe2S3 were also detected in the S-containing environment. The effects of Cl, Br and S2− on the corrosion behavior of 2Cr steel in the s-CO2 saturated aqueous environments were discussed.

INTRODUCTION

Before full decarburization can be achieved, the Intergovernmental Panel of Climate Change (IPCC) suggests an applicable way of combining CO2-producing processes with the carbon capture, utilization, and storage (CCUS) chain. Except for permanent CO2 storage, the economics and efficiency of CCUS processes can be further improved by utilizing the CO2 byproduct in other industry areas1,2. One of the promising methods is to use the captured CO2 for enhanced oil recovery (EOR). It is estimated by the U.S. Department of Energy that primary and secondary oil extraction processes produce about 33% of the oil present in existing reservoirs3,4. EOR techniques are utilized towards the end of an oil well's life span and seek to access the oil remaining. EOR techniques vary based on geologic conditions but involve the use of thermal or chemical agents to increase the mobility and displacement efficiency of the hydrocarbons in the reservoir. Noted that captured CO2 is typically compressed to a pressure above the critical point (7.4 MPa, 31°C) to avoid two-phase flow regimes. CO2 pipelines are usually operated at 40-60°C and 15-17 MPa5-7. In the ‘Criteria for Screening Reservoirs for CO2-EOR Suitability’ by the national energy technology laboratory (US) a reservoir that has undergone a successful waterflood is a prime candidate for CO2-EOR, typically with operating temperature < 121°C and pressure > 8.27 to 10.34 MPa8. Thus, CCUS-EOR systems deal with supercritical CO2 (s-CO2). Although CO2-EOR using CO2 as the injected solvent has considerable successful deployment examples in the oil industry9, the application of supercritical CO2 (s-CO2) for EOR is still quite new in this field.

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