271-5 Modeling the influence of Ferrihydrite on Underground Hydrogen Storage: Redox vs. Non-Redox

Session: Geologic Energy Resources and Storage for Now and the Future (Posters)

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Abstract:

Geochemical information on the viability and feasibility of hydrogen storage in subsurface formations of different lithologies is scarce. Iron (Fe), an abundant element in earth’s crust, plays a crucial role in regulating the geochemical interactions in subsurface reservoirs due to its potential to alter redox conditions. In this study, using abiotic reactive transport modeling in Geochemist's Workbench v18.0 X2t module, we evaluated the role of a geochemically abundant reactive amorphous iron mineral ferrihydrite six line (6L) in controlling the behavior of injected hydrogen in the subsurface reservoirs.

Upon injection of hydrogen, ferrihydrite, a Fe(III) phase gradually reduces to more reduced Fe(II) phases such as magnetite or soluble Fe(II). In our model, we used the maximum operational hydrogen partial pressure (100 bars) in subsurface reservoirs. The two dimensional reactive transport domain of 1 square meters was divided into 10×10 subdomains. The reactive domain mimics a sandstone block of known mineralogical composition and brine chemistry, which was reacted with 100 bars of gaseous hydrogen. Kinetic reduction rates obtained from previous literature were used for mineral dissolution and ferrihydrite reduction. Simulations run for 100 years demonstrate that ferrihydrite reduction is not only dependent upon hydrogen migration through the domain, but mostly dominated by the non-redox transformation into phases like goethite and magnetite in the presence of Fe(II). Rate of brine movement is also the main driver of such different transformation behavior, in addition to varying brine/mineral composition. pH directly alters such transformation, complying with prior experimental and field observations, as goethite formation may not be an intermediate step before complete reduction of Fe(III) phases. Overall, abiotic hydrogen consumption is minimal even after 100 years, although the progressive growth in partial pressure (pH₂) is spatially contrained due to the presence of reactive Fe(III) phases.

Our initial modeling calls for extensive experimental study on the different reactive amorphous phases of Fe(III). Long term hydrogen stirage can be successful with cushion gases such as CO₂, CH₄ which can alter the brine chemistry and mineralogy, thereby indirectly affecting the redox driven hydrogen oxidation. Considering the overall complexity for net consumption hydrogen gas in the subsurface, we need to carefully evaluate the activities of redox-sensitive ions like Fe for appropriate site selection.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-9998

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