Carbon steel corrosion in clay-rich environment

•We studied the steel corrosion under CO2 in clay-rich environment.•The steel corrosion under CO2 leads to a complex mineralogical paragenesis.•Under CO2, the results strongly contrast with similar experiments conducted under H2.•Under CO2, the corrosion rate slightly increases during the runs.

We investigated the carbon steel corrosion in carbon dioxide clay-rich environment to understand its behavior under geological conditions. The results show the formation of magnetite as the main corrosion product in the first step of the corrosion process, followed by the formation of different corrosion products with complex mixtures of iron-oxide, hydroxycarbonate, hydroxychloride and sulfide phases. These results strongly contrast with similar experiments conducted under H2 atmosphere where the major corrosion products consisted of iron sulfides. It appears then important to consider all the geochemical parameters including gas composition to better study corrosion of steel buried in geological formations.