Corrosion Behavior of Deep Water Oil Production Tubing Material under Supercritical CO_2 Environment: Part Ⅰ. Effect of Pressure and Temperature

摘要

The objective of the present study is to evaluate the corrosion properties of carbon steel in supercritical CO_2/brine mixtures related to the deep water oil production development. Corrosion tests were performed in 25 wt.% NaCl solution under different CO_2 partial pressures (4, 8, 12 MPa) and temperatures (65, 90°C). Corrosion behavior of carbon steel was evaluated by 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 slight difference with pressure. Under these conditions, the sample surface was locally covered by iron carbide (Fe3C) 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 very low value (～ 0.05 mm/y) due to the formation of protective FeCO_3 layer regardless the CO_2 partial pressure.