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Oilfield Corrosion Scales: A Surface Science Approach

Acres, Matthew

[Thesis]. Manchester, UK: The University of Manchester; 2018.

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Abstract

Corrosion is of huge interest to the oil and gas industry with an estimated annual cost of $1.372 billion. Sweet (CO2 rich) and sour (H2S rich) conditions can lead to corrosion of the interior walls of oilfield infrastructure. This corrosion not only results in metal loss but corrosion scales, which under advantageous conditions, can protect against further corrosion. Despite being an active area of research for 4 decades, the mechanistic details regarding the processes that lead to scale formation are not fully understood. The work conducted within this thesis aims to address this lack of understanding by the application of UHV-STM supported by LEED, AES and XPS to probe the initial interaction of species of interest (CO2/H2O/H2S) with a model single crystal iron substrate (Fe(110)). The exposure of CO2/H2O to the surface resulted in a wide range of overlayers observed in the parameter range explored (1 L/10 L/100 L at 25degC/100degC/200degC). Despite differences in dosing species and structural differences, the ordered overlayers were shown to be due to a single chemisorbed oxygen species. Notably an insight has been gained into an intermediary to the formation of a FeO(111) film on the surface of the sample. Exposures of H2S to the Fe(110) surface (100 L at 100degC and 200degC) resulted in the observation of a previously reported [2,1|1,2] overlayer, which was found to be resultant of a single chemisorbed sulfur species. Increasing exposure levels to 3x105 L at 25degC/100degC/200degC followed by post annealing in UHV (100degC/200degC) resulted in a range of nanostructured surfaces. The most commonly observed structure has been proposed to be similar in structure to FeS2(001), providing an insight into initial iron sulfide formation. In an attempt to expand beyond UHV studies, Near Ambient Pressure (NAP)-XPS has been used to probe the surface chemistry of an Fe(110) sample immersed in mbar pressures of a H2O/CO2 mixture. This revealed the formation of a weakly bound species on the surface that was not formed under exposure to H2O or CO2 individually. It has been tentatively attributed to the formation of a H2CO3 surface species, though further study is required.