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The underground storage of hydrogen (H$_{2}$) in porous rock formations offers a possibility for large-scale energy storage. However, hydrogenotrophic microorganisms can oxidize hydrogen through various metabolic processes e.g. sulfate or iron reduction, methanogenesis or acetogenesis. Since microorganisms can occur naturally or may be introduced through operational processes at the storage site, microbial processes must be considered when storing hydrogen in geological formations. In addition to hydrogen loss, microbial oxidation of hydrogen can also lead to other undesirable reactions, such as the formation of hydrogen sulfide, methane, organic acids, biofilms or corrosion. These reactions can affect the quality of the hydrogen as well as the storage performance.
Since the activity of microorganisms is determined by the in situ environmental conditions, it is also essential to understand the dependencies of microbial activity during hydrogen storage on the geochemical and mineralogical properties of porous rock formations in order to assess the potential effects of microbial activity during hydrogen storage.
Laboratory experiments simulating hydrogen storage with fluids from porous rock reservoirs showed hydrogen consumption, underlining the possibility of microbial activity during hydrogen storage (Dohrmann & Krüger 2023). In addition, experiments with pure cultures in batch incubation with minerals can help to better understand how microbial activity may be affected by porous rock material. Recent laboratory experiments in batch cultures have shown that hydrogen consumption by the methanogenic archaeon Methanothermococcus thermolithotrophicus was enhanced in the presence of rock material (Khajooie et al. 2024). The surface area was found to have a stimulating effect on the activity and that a formation-specific effect requires further investigation. So far, it is still unknown what role the surface plays and what mechanism controls the observed effects of rock material on microbial activity, including whether these effects are only temporary and how widespread they are. Therefore, further research on this aspect is needed. Preliminary results with two other hydrogen-consuming microorganisms did not show enhanced hydrogen oxidation in the presence of rock material.
In addition, porous rock formations also provide a habitat in which microorganisms may survive and persist. At the same time, biological processes like biomass accumulation, biofilm formation or microbially induced mineral precipitation might pose further challenges, as such activity might affect porosity and permeability of the porous rock reservoir. However, research on the impact of microorganisms on rock porosity and permeability is limited, mainly due to technical challenges in this research field. To simulate more in situ-like conditions a low-pressure flow-through system was used. M. thermolithotrophicus was successfully introduced into porous rock plugs while the anaerobic microorganisms stayed alive and active. At the same time, the setup was sensitive enough to detect a permeability reduction induced by the introduced microorganisms. This experimental workflow, which is a combination of batch incubations and flow-through experiments, allows us to study microbiology in direct relation to mineralogy. It will be used to gain further insights into the mechanisms that control microbial activity in rocks, as well as how microbial activity could affect the performance of a storage site.
| References | Dohrmann, A.B. & Krüger, M. (2023): Microbial (H$_{2}$) Consumption by a Formation Fluid from a Natural Gas Field at High-Pressure Conditions Relevant for Underground (H$_{2}$) Storage. Environmental Science & Technology, 57, 2: 1092-1102. DOI:10.1021/acs.est.2c07303 $\\$ $\\$ Khajooie, S., Gaus, G., Dohrmann, A.B., Krüger, M. & Littke, R. (2024): Methanogenic conversion of hydrogen to methane in reservoir rocks: An experimental study of microbial activity in water-filled pore space. International Journal of Hydrogen Energy, 50: 272-290. DOI:https://doi.org/10.1016/j.ijhydene.2023.07.065 |
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| Country | Germany |
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