Durability and integrity of well and rock materials for large scale underground hydrogen storage projects in porous reservoir: Insights from laboratory experiments

Large scale storage of hydrogen in porous reservoirs can buffer intermittent energy supply and demand in energy systems with large contributions of wind and solar energy. The efficiency of long term injection and withdrawal of hydrogen streams with large concentrations of hydrogen can be particularly affected by the long term interaction between hydrogen and rock or well materials in combination with cyclic pressure, temperature and stress changes during injection and withdrawal. Critical elements of hydrogen storage systems that may be affected are (1) the hydrogen gas stream, (2) the storage reservoir, (3) the caprock, (4) faults, (5) the well system, and (6) the surface environment. In particular, effects on the durability and integrity of well systems and on the mechanical and flow properties of porous sandstone reservoirs may impact the efficiency of storage operations. In this study, we show how results of laboratory experiments on rock and well materials at high pressure and temperature conditions can be used to assess effects of hydrogen exposure and cyclic pressure, temperature and stress changes on well systems and porous sandstone storage reservoirs. Key results of experiments on well cement (Portland type G), sandstone reservoirs, caprock and a scaled-down well system consisting of a casing, well cement and reservoir rock are reported. Samples were placed under relevant high pressure, temperature and stress conditions (100-200 bar, 50-100°C), both in an autoclave for reaction with H­₂ and N₂ and in a triaxial cell for testing injection/withdrawal scenarios. The results show (1) no major effects of H₂ exposure or cyclic loading on mechanical properties of well cement and reservoir sandstone under investigated conditions, (2) different behavior for sandstones exposed to N₂ (stiffer) and H₂ (less stiff) during cyclic loading, (3) some cumulative plastic deformation during cyclic loading of sandstone that may affect flow and mechanical properties, even in the elastic regime, (4) indications of increasing stiffness in caprock due to cyclic loading, (5) importance of casing-cement-reservoir interfaces as potential leakage pathways for hydrogen along wells, and (6) large effects of sample variations that complicate disentangling effects of N₂/H₂ exposure and cyclic loading. These results suggest that effects of interaction between hydrogen and rock or well materials in combination with cyclic pressure, temperature and stress changes during injection and withdrawal are limited for the investigated materials and conditions. However, they also emphasize the need for further research to understand the long-term effects of H₂ exposure and cyclic loading in different geological settings and under extended exposure durations.