Mechanical Property Changes in Well Cement Exposed to Hydrogen: From Molecular Dynamics to Storage Integrity

Abstract Understanding how hydrogen affects the mechanical behavior of wellbore cement is critical for ensuring the long-term integrity of underground hydrogen storage and natural hydrogen extraction systems. In this study, reactive molecular dynamics (MD) simulations were conducted to investigate the mechanical responses of two major cement hydration phases—calcium silicate hydrate (C-S-H) and ettringite—under both hydrogen-free and hydrogen-rich conditions. Uniaxial tensile loading was applied to quantify the influence of hydrogen on key mechanical properties, including Young's modulus, tensile strength, and toughness. The presence of hydrogen caused negligible mechanical degradation in C-S-H, whereas ettringite exhibited a substantial reduction in stiffness and strength, with a 54.6% decrease in Young's modulus and a 74.7% decrease in tensile strength. Density profile analysis revealed that hydrogen molecules preferentially infiltrated the voids within the ettringite structure but remained excluded from C-S-H. Furthermore, bond evolution analysis indicated that hydrogen altered the failure mechanisms of ettringite by disrupting Ca–O bonding and promoting a more ductile fracture pattern. These findings provide atomistic insights into hydrogen–cement interactions and suggest that ettringite is a critical weak phase affecting wellbore integrity in hydrogen-rich subsurface environments.