Speaker
Description
Underground hydrogen storage (UHS) in deep geological reservoirs is a promising technology for large-scale renewable energy storage. Hydrogen injection into the subsurface alters the chemical potential, resulting in a reducing environment that may trigger geochemical and microbial reactivity. This can lead to hydrogen conversion and loss, introduction of impurities, and pore clogging, impacting storage efficiency. Carbonate reservoirs, which make up a quarter of the potential UHS sites in Europe, are theoretically more susceptible to these types of reactivity. This is also true for pyrite-containing reservoirs (1–3), as the latter can react with hydrogen in redox reactions. While several studies have addressed reactivity during UHS, the extent and interactions of these reactions in carbonate aquifers, under reservoir-relevant conditions, remain unclear.
Recently, a pilot hydrogen injection and storage test was conducted in a karstified carbonate aquifer in Loenhout, Belgium, showing a shift in the microbial community and indications of (limited) reactivity upon hydrogen injection. In order to increase our understanding of these observed results and the behavior of such systems, we present here the results of a series of long-term laboratory-scale ambient- and high-pressure (80 bar) batch experiments under reservoir temperatures (65°C) and salinities (120g NaCl/L), with groundwater and crushed rock sampled from the Loenhout reservoir. We tested combinations of growth media with varying nutrient richness, different headspace compositions (hydrogen or nitrogen), and the presence or absence of crushed rock to simulate a range of subsurface conditions, including potential worst-case scenarios.
Preliminary results show low microbial cell counts (~10^3 cells/ml) in the sampled groundwater, with microbial communities initially mainly consisting of previously undiscovered species of sulfate reducing bacteria. Gas-phase analysis also indicates slow microbial reactivity. Moreover, after 19 months of laboratory incubations, cells appear to have been largely adsorbed on the crushed rock phase, without necessarily forming biofilms, suggesting a complex interplay between the solid phase and the microbial community. This may be the result of strong salinity-induced surface charge interactions between micro-organisms and calcite grains. This indicates that mineral surfaces play an important and potentially diverse role in the overall behavior of these systems, impacting availability of reactive minerals dissolved in the groundwater as well as the transport and retention of microbial cells. While further taxonomic analyses are ongoing to gain insight into community composition, our other results suggest slow and thus favorable reaction kinetics during UHS under the tested conditions. This outcome is important to verify the economic viability of hydrogen storage in carbonate reservoirs, which can play a crucial role in enabling the clean energy transition.
| References | A. Cavanagh, et al., “HyUSPRe Hydrogen Underground Storage in Porous Reservoirs Hydrogen storage potential of existing European gas storage sites in depleted gas fields and aquifers The HyUSPRe consortium” (2022), (available at www.hyuspre.euwww.hyuspre.eu). 2. J. P. Bensing, et al., Int. J. Hydrog. Energy. 47, 30621–30626 (2022). 3. L. Truche et al., Chem. Geol. 351, 217–228 (2013). |
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| Country | Belgium |
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