(573v) Hydrogen Storage in Silica-Kaolinite Shale and Its Impact on the Integrity: Molecular Modeling and Experimental Investigation

Hydrogen has emerged as an attractive alternative to traditional fossil fuels, offering potential as both a primary energy source and a versatile industrial raw material. Its attractiveness stems from its high specific energy capacity of 120-142 MJ/kg, widespread availability, and clean combustion product of only water vapor. However, challenges such as its lower volumetric and energy densities at room temperature, requirements for high-pressure vessel storage conditions (typically operated at 700 bar), and susceptibility to hydrogen embrittlement have complicated efforts to manage seasonal fluctuations in hydrogen supply and ensure long-term energy security. In response to these challenges, researchers have increasingly turned their attention to underground storage as a potential candidate. Previous investigations have explored hydrogen storage within pores of various minerals, revealing differences in uptake rates. Notably, studies have observed that hydrogen uptake tends to follow the order of illite > kerogen > kaolinite > quartz > calcite. However, much of the existing research has focused on the processes of adsorption and injection, often examining specific scenarios such as storage within calcite-rich carbonate or interactions with shale organic phases in the presence of shale gas.

Therefore, this research explores the potential to store hydrogen in a depleted shale gas reservoir which is silica (quartz (SiO₂)) -kaolinite(Al₂Si₂O₅₄) interface as it is closer to the natural shale reservoir. This investigation aimed to study the hydrogen adsorption affinity, H₂ reactivity in various conditions (temperature, pressure, gas mixtures, wet/dry environments) both theoretically and experimentally. The work is divided into several stages. Initially, Density Functional Theory (DFT) is employed to explore hydrogen adsorption, surface chemistry, and active adsorption sites on the interface. Subsequently, Reactive Force Field molecular dynamics (ReaxFF MD) is used to get an insight into hydrogen reactivity and replacement within the interface, considering a pure hydrogen environment as well as the presence of gas mixtures (CH₄/CO₂) and water vapor under typical of regional reservoir conditions (450 K and 500 bar). Finally, molecular modeling coupled with the experimental investigation to assess the impact of hydrogen adsorption/desorption on the shale integrity. This investigation spanned a range of temperatures from 50 to 100°C and pressures from 20 to 100 bar for understanding hydrogen behavior in this context. Then the shale samples were characterized through methods including Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), scanning electron microscope (SEM), and X-ray photoelectron spectroscopy (XPS) to a comprehensive understanding of how hydrogen interacts with shale under different conditions. The initial results revealed the physisorption of hydrogen on the shale surface, supported by low adsorption energies (0.04 to -0.21 ev) and by Bader charge analysis indicating no charge transfer. This work has successfully shown the potential of depleted shale gas reservoirs to store hydrogen as less hydrogen will penetrate through the shale surface so hydrogen loss risk will be reduced, and it can be stored to supply the energy demand.