Experimental investigation of the impact of short-term hydrogen exposure on cement sheath's mechanical and sealing integrity

Abstract

The effect of hydrogen exposure on cement is a topic of great interest due to its significance in the safety and security of Underground Hydrogen Storage (UHS) in geological structures. Any alteration to cement properties can affect the wellbore isolation capacity or induce premature failure, compromising the reliability and safety of UHS projects. While over the past decade, various studies have been conducted on this topic, the effect of hydrogen on cement's mechanical and sealing integrity remains unclear. This study aims to evaluate the impact of different short-term hydrogen exposure timeframes on the performance of Class H neat cement under geological storage conditions. Multiple cement samples were prepared, cured, and exposed to pure H₂ for 7, 14, 21, and 28 days in a core holder at controlled pressure and temperature conditions (49 °C, 10.34 MPa). The effect of hydrogen on cement's sealing abilities was evaluated by monitoring alterations in petrophysical properties like porosity and permeability. Cement's mechanical integrity was evaluated by measuring properties such as Young's Modulus, Poisson's ratio, Unconfined Compressive Strength, and Tensile Strength before and after exposure. Other techniques like Computer Tomography (CT) scanning and Scanning Electron Microscopy (SEM) coupled with Energy Dispersive Spectroscopy (EDS) were used to further understand cement's interaction with hydrogen. The most significantly affected properties were permeability, ultimate strengths, and elastic properties. The creation of microfractures following the hydrogen pressurization for 14, 21, and 28 days was observed, which suggests cement presents a less rigid behavior under these conditions. Variations in cement compositional elements were found, with predominant reductions in Calcium (Ca) and Oxygen (O), as well as Carbon (C) enrichment. The results of this study provide a further understanding of hydrogen effects on cement's mechanical and sealing integrity and valuable insight into the wellbore integrity implications in UHS projects.