Contrasting the Formation Integrity and Geomechanical Response of Underground Methane and Hydrogen Storage at Equivalent Energy Density

Underground gas storage is increasingly considered for renewable-based hydrogen as part of the energy transition. However, hydrogen has a much lower energy density than methane, requiring significantly larger injected volumes to deliver the same stored energy. The geomechanical consequences of this difference remain largely unexplored.

We investigate the impact of replacing methane with hydrogen on subsurface stress conditions and caprock integrity using a coupled two-phase flow and geomechanical model of a dome-shaped aquifer in northern Spain. Five years of seasonal storage cycles are simulated for both gases under equivalent energy storage conditions. Changes in pore pressure and stress are evaluated using the Mohr–Coulomb failure criterion.

Results show that hydrogen storage induces larger pore-pressure increases, leading to a stronger reduction in effective stress and higher mobilized friction coefficients compared to methane. In several areas, hydrogen storage approaches commonly adopted stability thresholds, whereas methane storage remains mechanically stable. These findings emphasize the need for dedicated geomechanical assessments when transitioning from methane to underground hydrogen storage.

 

Acknowledgments

This research was supported by the ‘‘Ministerio de Ciencia, Innovación y Universidades’’, Spain and ‘‘Agencia Estatal de Investigación’’, Spain (10.13039/501100011033) and by ‘‘ERDF/EU’’, through grant HydroPore II (PID2022-137652NB-C43).