A Critical Review on Transport and Mechanical Property of Well Cement for Underground Hydrogen Storage

Underground hydrogen storage (UHS) in geological formations is emerging as a critical solution for large-scale, long-duration energy storage to support the hydrogen economy. A key challenge for UHS is ensuring well integrity, especially the performance of well cement that seal the casing and formation. This review provides a comprehensive literature survey of transport and mechanical properties of well cement under hydrogen exposure. We first outline the motivation for UHS and the importance of wellbore integrity in preventing hydrogen leakage. Next, we discuss oil and gas well cement types (with emphasis on API Class G Portland cement) and standard cement property measurements. The core of the review synthesizes findings from the past 15 years on how hydrogen impacts cement porosity, pore size distribution, permeability, diffusivity, and mechanical strength. Conflicting results are reconciled: some studies report hydrogen-induced degradation (increased porosity, microcracking, strength loss), whereas others observe minimal or even beneficial effects (pore refinement, strength gain) under certain conditions. Advanced microscale characterization techniques are examined for their role in elucidating hydrogen–cement interactions at the pore scale. We also review image-based modeling approaches that leverage 3D imagery of cement microstructure to simulate transport (diffusion, permeability) and mechanical behavior. Overall, hydrogen is less chemically reactive with cement than aggressive gases like CO2, but its small molecular size and high diffusivity pose unique risks for leakage through defects. This review highlights that current studies on hydrogen–cement interactions face key limitations: poor reporting of experimental details reduces reproducibility, image-based modeling is rarely applied, and most work overlooks detailed pore structure. These issues lead to inconsistent results and hinder understanding of hydrogen's effects on cement. We conclude with an outlook on research needs for ensuring well cement integrity in future UHS projects.