Abstract

The global drive for clean energy and carbon reduction has placed hydrogen (H₂) at the forefront of the energy transition. Saudi Arabia is uniquely positioned to leverage both blue hydrogen (produced from natural gas with carbon capture) and green hydrogen (from renewable sources) to achieve its net-zero emissions goal by 2060. As hydrogen becomes pivotal for decarbonizing industries and enhancing energy sustainability, large-scale initiatives like the NEOM Green Hydrogen Project underscore Saudi Arabia’s leadership in H₂ production. To fully unlock hydrogen's potential, optimizing underground hydrogen storage (UHS) is critical. This dissertation investigates the key factors influencing H₂ storage in geological formations, providing foundational knowledge to support UHS development in the region.

This dissertation explores key mechanisms influencing H₂ storage, including thermodynamics, gas mixing, mineralogy, and organic content. Experimental investigations focus on trapping mechanisms like structural, residual, solubility, and adsorption trapping and assess how cushion gases like methane (CH₄), variations in total organic content (TOC), and mineralogy impact storage efficiency.

Thermodynamic modeling using cubic and non-cubic equations of state (EoS) demonstrates that PC-SAFT and GERG2008 EoSs outperform classical cubic-EoS models in predicting H₂ properties for gas mixtures. Advanced cubic EoSs, such as SR-SRK, also deliver high accuracy, providing robust tools for simulating UHS scenarios under diverse reservoir conditions. Experimental studies on H₂ solubility reveal that gas impurities, particularly CO₂, significantly alter storage efficiency and safety, highlighting the importance of impurity management.

The role of mineral composition and TOC in H₂ structural trapping is explored using Jordanian oil shale, where TOC-rich samples exhibit enhanced H₂ adsorption. Variations in calcite and quartz content were found to influence wettability and structural trapping potential. The study also evaluates the effects of gas mixing on wettability and interfacial tension in H₂/brine, H₂-CH₄/brine, and CH₄/brine systems, demonstrating how gas composition impacts UHS performance.

Nanomaterials, specifically silica and alumina nanofluids, are investigated for their ability to improve H₂ storage efficiency by altering rock wettability. These nanofluids convert shale and carbonate formations from hydrophobic to hydrophilic, enhancing caprock integrity and capillary trapping capacity.

Gas adsorption isotherms and kinetics are also analyzed, comparing the behaviors of H₂, CO₂, and CH₄ in Jordanian organic-rich shale. CO₂ demonstrates faster and preferential adsorption over H₂, validating its effectiveness as a cushion gas for UHS. Comparative studies on six shale samples (Qusaiba, Marcellus, Barnett, Eagle Ford, and two Jordanian shales) further highlight competitive adsorption under geological conditions. The behavior of pure H₂ and H₂-CH₄ mixtures (50-50% and 75-25% ratios) is also examined, showing that methane stabilizes H₂ adsorption, enhancing uniformity and improving storage and retrieval efficiency.

This dissertation provides comprehensive insights into the thermodynamic, mineralogical, and adsorption mechanisms critical for optimizing UHS systems. The findings offer practical strategies for improving H₂ storage security, advancing low-carbon energy solutions, and supporting the global energy transition.