Chemical analysis of the initial corrosion layer on pipeline steels in simulated CO2-enhanced oil recovery brines

The surface layers of two model steels after corrosion in simulated CO2-enhanced oil recovery brines were characterized by chemical analysis and ion release measurement. It was found that a thin double layer of FeCO3 and FeO was formed on 20-steel surface, which can act as an initial pseudo-passive layer; while for 3Cr-steel, a thick, incompact corrosion layer with graded structures was formed, triggering higher dissolution rate of steel surface until reaching critical thickness. The results reflect an underlying mechanism of surface structural changes during initial CO2 corrosion, which also gives indications for long-term corrosion performance.

► The corrosion behavior of 20-steel and 3Cr-steel in CO2-EOR brines was studied.
► The formation of surface layers was analyzed by XPS and ion release monitoring.
► Pseudo-passive layer was formed on 20-steel surface.
► Higher corrosion rate would be triggered by initial surface layer on 3Cr-steel.