The Solubility of H2 in NaCl Brine at High Pressures and High Temperatures: Molecular Simulation Study and Thermodynamic Modeling

To address the energy demands of a growing population and mitigate carbon emissions, it is imperative to transition from fossil fuels to renewable energy sources. However, the intermittency of renewable energies poses a significant challenge. To address this issue, deep saline aquifers have emerged as a viable option for large-scale energy storage, particularly through hydrogen (H 2 ) storage post Power -to -Gas process. Moreover, natural H 2 emissions have been documented worldwide, and the potential for underground accumulations presents promising zero -carbon energy sources. However, in these different contexts, the interaction between gas, brine, and rock can lead to physico-chemical and biochemical phenomena that can directly impact the mobility and stability of H 2 . Therefore, understanding the thermophysical behavior of the involved fluids is essential for the development Underground Hydrogen Storage in porous media and for exploring natural H 2 reserves. However, despite recent advancements, there is still a lack of experimental data on thermophysical properties of hydrogen in contact with brine. This study investigates the equilibrium of the H 2 /brine system using Continuous Fractional Component Monte Carlo molecular simulation through two methods: the Gibbs ensemble method and the isobaric -isothermal simulation based on Henry ' s law. Different force fields for H 2 , water and salt (NaCl) ions were evaluated. Through a comparative analysis, two model combinations, Marx-TIP4P/EP-KBF and MarxTIP4P/2005-Madrid, were identified as providing the most accurate results, albeit requiring a constant binary interaction for enhanced H 2 solubility quantification in brine. After adjustment to some limited experimental data from literature, the simulations were extended to higher temperatures (up to 453 K), pressures (up to 100 MPa), and NaCl salinities (up to 6 mol/kg w ). Finally, the newly generated data facilitated the refinement of a thermodynamic model using the Krichevsky and Kasarnovsky approach, improving estimations of H 2 dissolution losses, caprock sealing capacity, and insights into natural H 2 production and accumulation underground.