Speaker
Description
Due to the demand for large subsurface storage volumes for hydrogen produced by renewable energy, different porous reservoir rocks and the related cap rocks are being investigated in Germany. The geochemical redox reactions involving either the reduction of iron in iron(III)oxides (hematite) or the reduction of sulfur in FeS(-I) sulfides (pyrite) is a not well quantified risk, even if regarded as much slower than possible microbial oxidation reactions. Therefore, different experimental avenues have been taken in the past years to understand the reactions, and quantify the rates of individual reactions and determine possible limiting factors. Up to now experiments predominantly have been carried out in static batch type reactors (e.g. Thüns et al 2019, Truche et al 2010) on sieved mineral grains with diameters near 100 µm. In these systems the evolving boundary layer on the grains – or the reaction front – may significantly retard the overall reaction progress, as the transport of the reduced products, i.e. ferrous iron or sulfide, away from the reaction front is strongly inhibited by absence of mixing or turbulence.
Therefore we developed a set of flow-through experiments aiming to investigate the magnitude of suppression of the apparent rates of hydrogen oxidation/iron or sulfur reduction. One avenues was to investigate the rates of hydrogen oxidation and iron (and sulfide) release near in situ temperatures and pressures in high-pressure gold-coated flow cells. The other avenue being developed is using microfluidic systems to be able to follow not only the oxidation of hydrogen and release of reduced products, but also to possibly delineate if these products might reprecipitate in the downstream part in chemical or physical gradients in the inhomogeneous flow system. For this, the reactions between hydrogen and the evolving pyrite/pyrrhotite or hematite/magnetite surfaces were monitored by in situ microscopy and operando Raman spectroscopy in a dedicated microfluidic system. In contrast to the processes in batch type reactors dominated by direct dissolution-reprecipitation processes for e.g. the evolving hematite-magnetite surface (cf. Ostertag-Henning & Plümper, 2024), the sites of redox reaction and dissolution in flow systems frequently are upstream of the site of secondary precipitation, increasing the risk of reducing pore throat diameters and flow conditions if the extent of the reactions is significant.
| Country | Germany |
|---|---|
| Water & Porous Media Focused Abstracts | This abstract is related to Water |
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