Corrosion Behavior of High Temperature and O2 Content on Gas Pipelines in CO2/H2S/O2 System

With the rapid development of industries such as transportation and petrochemicals, the demand for energy such as oil and natural gas continues to increase. Heavy oil reservoirs that account for a large proportion of petroleum resources have attracted the extensive attention of a large number of scholars. For example, multi-component thermal fluid flooding was adopted as an effective technology to recover heavy oil in Xinjiang Oilfield. The high temperature and strong corrosive medium will directly accelerate the corrosion of the gas pipelines due to the high temperature of the multi-component thermal fluid, which poses a huge threat to the safe operation of the gas pipelines in Xinjiang Oilfield. In this article, to provide a basis for corrosion prevention and control of gas pipelines in Xinjiang Oilfield, the corrosion behavior of L360NS steel was researched by the corrosion weight loss method under different O2 content (0-2mol%) and temperature (60-180 ℃) in CO2/H2S/O2 coexistence system. The experimental scheme of high temperature and high-pressure autoclaves is formulated by operating conditions of the gas pipelines in the Xinjiang oilfield in this paper. The corrosion solution is simulated formation water, and the experimental sample is an L360NS steel pipe. Surface characterization of corrosion scales using SEM, EDS, and XRD showed that O2 content (0mol %-2mol%) and temperature (60-180 ℃) notably changed the characteristics of corrosion scales. The results showed that the average corrosion rate of L360NS steel gradually increased from 0.299 1 mm/a to 0.912 3 mm/a with the increased O2 content (0-2mol%). The corrosion product film is of different shapes as wedge-shaped and polycrystalline and corrosion defects showed a gradually enlarging trend on the surface of the samples. There are two reasons why O2 content affects the corrosion rate. The appearance of loose and porous Fe high-valent oxides is due to the strong oxidizing and depolarizing effects of O2 on the surface of the corrosion product. Depolarization and strong oxidization generate high-valent oxides of Fe (such as Fe2O3, and Fe3O4), the product film structure gradually becomes loose, the protection performance decreases, and the corrosion degree is deepened. The synergistic effect of O2 and H2S generates elemental S, and elemental S is easily hydrolyzed in solution to generate H2SO4, which will induce the formation of local corrosion defects in the low pH area, further promoting local corrosion. The average corrosion rate of L360NS steel gradually decreases from 2.103 4 mm/a to 0.457 0 mm/a with the increase in temperature (60-180 ℃). Corrosion defects are gradually reduced and the structure of corrosion product film changes from porous to dense gradually. The corrosion product of Grain-like products decreases and grains become smaller, polygonal crystal-like products increase. The temperature mainly affects the product film's structure to inhibit steel's corrosion. In CO2/H2S/O2 corrosive coexistence system, the higher temperature promotes the corrosive reaction kinetics to a certain extent, but the higher temperature will promote the formation of FeCO3, resulting in a dense corrosion product film structure that hinders the contact between the corrosion medium and the substrate and inhibits corrosion. © 2023 Chongqing Wujiu Periodicals Press. All rights reserved.