(197bk) Thermophysical Properties of H2/Gas/Brine System Under Subsurface Storage Conditions: Molecular Simulations and Thermodynamic Modeling

Deep saline aquifers seem to be a very promising solution for large-scale hydrogen storage (following a Power-to-Gas process) due to their capacity, their storage over a long period (providing sufficient storage capacity for seasonal energy demands) and their geographical availability [1, 2]. Given the limited knowledge of this type of storage, it is important to study the different phenomena that can impact the quality of the stored gas. In aquifers, the interaction between gas, brine and rock can lead to various physicochemical and biochemical phenomena that can impact the stability and mobility of hydrogen, including dissolution, diffusion and reactivity, etc. To study and develop such infrastructure, it is essential to have a comprehensive understanding and quantification of the thermophysical properties involved, such as gas/liquid solubility, diffusion, interfacial tension, and others [3].

For reasons of complexity, cost and hazardousness, experimental studies on the thermophysical properties of H₂/NaCl brine systems are limited. Few studies (2 experimental and 2 molecular simulation studies) were performed on the phase equilibria of H₂/NaCl brine systems [4-7], showing significant discrepancies, and only recently interfacial tension were evaluated [8, 9]. Regarding the transport properties, no experimental studies are available for the self-diffusivity of H₂/H₂O/NaCl mixtures, and only one recent molecular simulation study has been published [7]. Furthermore, almost no studies deal with more representative systems consisting of mixtures of gases (H₂, CH₄, CO₂, etc.) and ionic species in the formation water.

In this work, new equilibrium data for H₂/gas/brine systems are predicted using Monte Carlo simulation with different approaches [10]: Gibbs ensemble method (direct method) and single NPT simulation using Henry's law method (indirect method). The effect of density and excess properties on solubility prediction is studied using different force fields for hydrogen, gas, water and salt ions. In addition, the possible influence of clay interlayer on the solubilities is explored. Using molecular dynamics, new data on self-diffusivity and interfacial tension for H₂/NaCl brine systems are provided for a wide range of conditions relevant to underground hydrogen storage in porous media.

After validation against laboratory experiments, data are used to develop thermodynamic models with different approaches (gamma-phi and phi-phi approaches) and transport properties correlations. The developed models can be implemented in large-scale simulation tools, providing a more reliable representation of thermophysical property data and a better estimation of storage capacities and sealing integrity.

References

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2. Muhammed, N.S., et al., A review on underground hydrogen storage: Insight into geological sites, influencing factors and future outlook. Energy Reports, 2022. 8: p. 461-499.
3. Heinemann, N., et al., Enabling large-scale hydrogen storage in porous media–the scientific challenges. Energy & Environmental Science, 2021. 14(2): p. 853-864.
4. Chabab, S., et al., Measurements and predictive models of high-pressure H2 solubility in brine (H2O+ NaCl) for underground hydrogen storage application. International Journal of Hydrogen Energy, 2020. 45(56): p. 32206-32220.
5. Torín-Ollarves, G.A. and J.M. Trusler, Solubility of hydrogen in sodium chloride brine at high pressures. Fluid Phase Equilibria, 2021. 539: p. 113025.
6. Lopez-Lazaro, C., et al., Predicting the phase behavior of hydrogen in NaCl brines by molecular simulation for geological applications. BSGF-Earth Sciences Bulletin, 2019. 190(1): p. 7.
7. van Rooijen, W., et al., Interfacial Tensions, Solubilities, and Transport Properties of the H2/H2O/NaCl System: A Molecular Simulation Study. Journal of Chemical & Engineering Data, 2023.
8. Hosseini, M., et al., H2− brine interfacial tension as a function of salinity, temperature, and pressure; implications for hydrogen geo-storage. Journal of Petroleum Science and Engineering, 2022. 213: p. 110441.
9. Higgs, S., et al., In-situ hydrogen wettability characterisation for underground hydrogen storage. International Journal of Hydrogen Energy, 2022. 47(26): p. 13062-13075.
10. Kerkache, H., et al., Solubility of H₂ in water and NaCl brine under subsurface storage conditions: measurements, molecular simulations and thermodynamic modeling. International Journal of Hydrogen Energy, (in Press, 2023).