Impurities Associated with Underground Hydrogen Storage (UHS) - Material Integrity Concerns and Mitigation Processes

Abstract The hydrogen industry has been progressing towards increasing hydrogen transport in recent years. With the drive toward increasing hydrogen transportation, hydrogen embrittlement and parameters impacting the process have been scrutinized. While in smaller scale hydrogen projects, long-term hydrogen storage has not been a primary concern, the large-scale deployment of hydrogen demands safe and efficient long-term and high-volume storage options. Therefore, geological reservoirs, including depleted oil and gas fields have been considered for large-scale underground hydrogen storage (UHS) as they have been safely used for CH4 storage for decades. However, microbial activities in UHS are more significant compared to that of CH4 considering that molecular hydrogen is one of the main electron donors for microbial respiration in the subsurface. This demands an understanding of the subsurface microbial biosphere as well as those contaminants absorbed from the reservoir and introduced during drilling, pumping and mining. This contamination can have adverse impacts on the material integrity of both the downhole equipment as well as the above ground transport network for transporting back produced hydrogen. Since selecting resistant materials is not always economically viable, mitigation strategies – including appropriate purification processes – are likely essential for hydrogen repurposing projects. This paper discusses different impurities and how they contribute to a corrosive environment endangering material integrity of the network through a potential synergistic effect with hydrogen embrittlement. Additionally, the potential purification process that can be employed to minimize such impacts will be discussed.