Experimental Investigation of Cement Compatibility in Underground Hydrogen Storage in Depleted Reservoir

Underground Hydrogen Storage (UHS) is a method to store a large amount of energy to manage its seasonal fluctuations. The selection of proper well materials is a critical aspect, considering the small size of the molecule of H2 and its strong diffusivity. Its impact on materials shall be deeply evaluated and investigated. The work described in this document analyzes the interaction of standard cement slurries used in oil and gas fields with hydrogen at standard reservoir conditions. The cement-hydrogen interaction tests were designed and conducted using the methodological approach typical of the materials/fluids compatibility tests; an autoclave was used as key instrumentation to simulate reservoir temperature and pressure conditions. The samples were left inside the autoclave in contact with hydrogen, at reservoir temperature and pressure condition (90 °C and 150 bar), for 8 weeks. In parallel to the aging in hydrogen, twin samples were aged in an inert atmosphere (nitrogen) for comparison. The effects of the long exposure of the cement to H2 have been analyzed by observing the changes in the chemical-physical properties of the cement itself. To give evidence of the goodness of the cement as a well sealant material in the UHS, compressive strength, saturation and permeability, chemistry of the cement were measured/analyzed pre- and post-hydrogen exposure. In addition to the tests, a theoretical analysis performed using thermodynamic modeling software was also conducted to validate test results. The thermodynamic analysis was focused on the specific interaction of the species, hydrate and not-, constituting the cement and the hydrogen, investigating the spontaneity of the redox reactions that could take place. Preliminary autoclave experimentation results show that hydrogen does not alter overly chemical and physical characteristics of cement samples. This compatibility study of Hydrogen with cement is the first important step to further de-risk any UHS activity. The engineered and adopted testing protocol reported in this paper proved to be effective for the purpose of the study and could be applied for the validation of specific cement slurries in the UHS contexts.