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The objective of the present study was to evaluate the corrosion properties of carbon steel in supercritical carbon dioxide (CO 2 )/brine mixtures related to the deep water oil production development. Corrosion tests were performed in 25 wt% sodium chloride (NaCl) solution under different CO 2 partial pressures (4,8, 12 MPa) and temperatures (65°C, 90°C). Corrosion behavior of carbon steel was evaluated using electrochemical methods (linear polarization resistance [LPR] and electrochemical impedance spectroscopy [EIS]), weight-loss measurements, and surface analytical techniques (scanning electron microscopy [SEM], energy-dispersive x-ray spectroscopy [EDS], x-ray diffraction [XRD], and infinite focus microscopy [IFM]). The corrosion rates measured at 65°C showed a high corrosion rate (~10 mm/y) and a slight difference with pressure. Under these conditions, the sample surface was locally covered by iron carbide (Fe 3 C), which is porous and non-protective. However, the corrosion rates measured at 90°C increased with time at the initial period of the test and decreased to a very low value (~0.05 mm/y) due to the formation of protective iron carbonate (FeCO 3 ) layer regardless the CO 2 partial pressure.

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Deep water oil production tubing materials are exposed to high carbon dioxide (CO 2 ) pressure and temperature conditions that can affect the corrosion performance of such materials. The present study evaluated the corrosion behavior of carbon steel exposed to supercritical CO 2 /oil/brine mixtures at different water cuts (0, 30, 50, 70, and 100%), CO 2 partial pressures (8 MPa and 12 MPa), and temperatures (65°C and 90°C) in a flowing 25 wt% sodium chloride (NaCl) solution. Corrosion behavior of carbon steel was evaluated by using electrical resistance (ER) measurements, weight-loss measurements, and surface analytical techniques (scanning electron microscopy [SEM] and energy-dispersive x-ray spectroscopy [EDS]). The corrosion rates of carbon steel increased with increasing water cut. There was no indication of corrosion attack with 0% water cut. At lower water cuts (30% and 50%), the steel surface was covered by iron carbonate (FeCO 3 ), while iron carbide (Fe 3 C) was present on the steel surface at higher water cuts (70% and 100%) with very high corrosion rates. In addition, the presence of flow prevented the formation of protective FeCO 3 at high water cut conditions.

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