Two methods to prepare tungsten/tungsten oxide as reference electrode for performing electrochemical measurements in H2O-saturated super critical (SC) CO2 phase in the study. The W/Woxide reference electrodes are fabricated using electrochemical or thermal oxidation.
The stability of each type of tungsten/tungsten oxide electrodes is verified by comparing the potential in brine solutions containing MEG up to 100°C with exposure time over 48 hours. The results are consistent with literature that the reference potential decreases with the increase in temperature. The results also show that the thermal-prepared W/Woxide reference electrode is stable at high temperature.
The W/Woxide reference electrode is employed to electrochemically test carbon steel (Q-125) in the SC-CO2 at 65°C. It is found that the W/Woxide reference electrode can be used for studying the electrochemical mechanism of carbon steel corrosion in SC-CO2, assessing the effect of changing oxidizing conditions of the SC-CO2 environment on the carbon steel corrosion kinetics.
A good reference electrode has to provide advantages like fast pH response, high corrosive resistance, and harsh-environmental reliance.1-4 Although common reference electrodes like glass reference electrode already possesses excellent pH response, it cannot be counted as a reliable tool in a harsh environment of high temperature and high pressure like the pipelines.
Super critical (SC) CO2 is common occurrence in enhanced oil recovery (EOR), which has been attracted extensive interests for many years, since the supercritical fluid has not only the dissolution ability of liquid phase, but also the flowing behavior of gas phase.5 Both behaviors further can largely decrease the cost of CO2 transportation.6
Supercritical environment is defined as a phase where liquid and gas phases are beyond critical point and coexisted at high temperature and high pressure. As the temperature increases, the boundary between liquid and gas phases will gradually disappear, and the individual behavior of each phase will not be clearly shown anymore after crossing the critical point.