Toward accurate subsurface simulation for underground hydrogen storage: EOS evaluation and viscosity model optimization

Underground hydrogen storage (UHS) involves complex subsurface processes, where accurate modeling of density and viscosity is essential for reliable simulations. In this study, a comprehensive experimental databank of density and viscosity for pure hydrogen and binary hydrogen mixtures with potential cushion gases (CH 4 , N 2 , and CO 2 ) is assembled. Using this databank, commonly applied cubic equations of state (EOS)—van der Waals, Peng–Robinson, and Soave–Redlich–Kwong—with and without Peneloux volume shift are systematically benchmarked against the GERG-2008 equation of state using both experimental data and a synthetic full-range thermodynamic grid, and their performance is evaluated through a multi-criteria assessment jointly considering density and viscosity predictions. The results show that GERG-2008 consistently outperforms cubic EOS in predicting density and viscosity, especially for H 2 CO 2 mixtures. While SRK and PR-Volume Shift show acceptable accuracy for density—particularly for H 2 CH 4 and H 2 N 2 mixtures—their performance in viscosity predictions, especially for H 2 CO 2 mixtures, is significantly less reliable. Nearly 200 times greater computational time for GERG-2008 compared to cubic EOS represents a clear trade-off between accuracy and computational efficiency. Newly optimized coefficients for the Lohrenz–Bray–Clark (LBC) viscosity model are proposed, dedicated separately for methane–hydrogen and carbon dioxide–hydrogen mixtures. These tailored coefficients enhance viscosity prediction accuracy within their respective systems. The findings highlight the limitations of cubic EOS in accurate thermophysical property modeling while showing favorable computational efficiency. This work also identifies gaps in experimental data and suggests directions for future research. • Comprehensive databank for ρ & μ in H 2 and its binary mixtures with CH 4 , N 2 , CO 2 . • Benchmark GERG-2008, PR, SRK ( ± volume shift) and vdW vs experimental data. • GERG-2008 outperforms cubic EOS, especially for H 2 CO 2 mixtures. • SRK & PR-VolumeShift suit density; H 2 CO 2 viscosity errors remain high. • Tuned LBC for H 2 CH 4 & H 2 CO 2 mixtures to predict viscosity.