Corrosion Behavior of Deep Water Oil Production Tubing Material Under Supercritical CO2 Environment: Part 2—Effect of Crude Oil and Flow

Abstract

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.

Corrosion behaviors of steels under supercritical CO2 conditions

“…There was no corrosion attack observed with 0% water cut, and below 50% water cut, the corrosion rate of carbon steel slightly increased with the increase of water cut, while once the water cut exceeded 50%, the corrosion rate increased significantly. However, no localized corrosion was observed in the study of Farelas et al (2013b) for different water cuts.…”

“…The flow structure completely changed into oil-in-water state while the water cut in the mixture was over 50%. Farelas, Choi, Nesic, Magalhaes, and Andrade (2013b) also argued with this view that the transition point from water-in-oil state changing to oilin-water state was 50%. There was no corrosion attack observed with 0% water cut, and below 50% water cut, the corrosion rate of carbon steel slightly increased with the increase of water cut, while once the water cut exceeded 50%, the corrosion rate increased significantly.…”

Effect of CO2 Partial Pressure on the Corrosion Behavior of J55 Carbon Steel in 30% Crude Oil/Brine Mixture

“…The variation trend of the penetration rate/average corrosion rate ratio of the J55 carbon steel surface was the same as that of the maximum corrosion depth as the CO 2 partial pressure was increased. The penetration rate/average corrosion rate ratios were greater than 4, indicating that local corrosion occurred on the surface of the carbon steel [ 8 , 18 ]. At P = 1.0 MPa, the corrosion depth was the largest at 382.742 μm, which corresponded to 69.8504 mm/a.…”

“…The acceptable rate of wellbore corrosion in China is less than 0.076 mm·year −1 [ 6 ], and the qualitative categorization of carbon steel corrosion rates for oil production systems in the US includes low (<0.025 mm·year −1 ), moderate (0.025–0.12 mm·year −1 ), high (0.13–0.25 mm·year −1 ), and severe (>0.25 mm·year −1 ) [ 7 ]. When water cut is greater than 50%, the corrosion rates of carbon steel (API 5CT L80) and P110 steel are 3.4–34.2 and 0.03–5.0 mm·year −1 , respectively [ 8 , 9 ], which are far beyond the acceptable range. Thus, many studies have focused on CO 2 corrosion, especially on the effect of environment on corrosion.…”

Pitting Corrosion and Microstructure of J55 Carbon Steel Exposed to CO2/Crude Oil/Brine Solution under 2–15 MPa at 30–80 °C

“…For example, the corrosive medium and environment have been identified as the deciding factors of corrosion rate and morphology. The influence of temperature and pressure on corrosion rate is mainly reflected by the changes that they induce in the protectiveness of the corrosion product layer [7,8,9,10,11,12,13,14,15,16,17,18]. These changes, in turn, lead to changes in the corrosion rate.…”