Speaker
Description
Geological storage of hydrogen (H₂) is now considered a major strategic pillar to support the energy transition. However, several questions remain regarding the risks associated, especially in the event of a slow H₂ leak toward shallow subsurface environments, which constitute the final natural barrier before surface emission. Improving our understanding of H₂ reactivity and its influence on microbial processes in aquifers is therefore essential. Reliable monitoring approaches are required to detect H₂ directly (H₂ concentrations in dissolved and gaseous phases) or indirectly (CO₂, O₂, N₂ in dissolved and gaseous phases, ionic balance, trace elements, redox conditions).
Between 2017 and 2021, Ineris conducted the first in situ experiments at the Catlab experimental site located in the Paris basin (Catenoy, France). A simulated H₂ leakage was created by injecting groundwater saturated with dissolved H₂ into the shallow chalky aquifer (~20 m deep). This unconfined aquifer contains groundwater of calcium–bicarbonate facies with a near-neutral pH. A network of eight piezometers and four dry boreholes enabled monitoring in both saturated and unsaturated zones. The site was equipped with advanced geochemical instrumentation, including a gas-completion well coupled to Raman and mid-IR probes. A total of 5 m³ of H₂-saturated groundwater was injected into the aquifer, following a tracer injection to track plume migration. Complementary sampling enabled characterization of ionic and trace-element responses associated with the simulated leakage. These initial tests revealed short-term physicochemical perturbations following H₂ injection (decrease of redox, O2, CO2, electrical conductivity, bicarbonate ions…) but too brief to allow a reliable evaluation of H₂ biodegradation or microbial community dynamics.
To overcome this limitation, a laboratory column experiment was designed to reproduce, over several weeks, the geochemical and microbial evolution of an aquifer exposed to H₂. Groundwater from the Catlab site was saturated with H₂ and circulated through a sediment-filled column. This aimed to evaluate the potential stimulation of hydrogenotrophic, denitrifying, or sulfate-reducing communities through a multi-scale monitoring strategy, combining measurements and sampling.
Daily measurements included continuous monitoring of outlet flow rate, dissolved H₂ concentration in the column outflow, and key physicochemical parameters. The column itself was weighed daily to detect possible variations in water content, microbial development or gas retention within the porous medium. Weekly monitoring focused on the hydrochemical and microbiological evolution of water samples and porous material, enabling quantification of major and minor ions, trace elements, as well as assessment of microbial abundance, viability, and shifts in community structure: we noted variations in nitrates, nitrites and bicarbonates. In addition, targeted analyses using quantitative PCR and high-throughput sequencing were performed. Two dedicated samples, taken at the beginning and end of the experiment, allowed the identification and quantification of functional microbial groups potentially involved in H₂ consumption.
Overall, this work provides new insights into hydrogen reactivity, associated geochemical perturbations, and microbial responses in shallow aquifer systems, combining results from in situ experiments and controlled laboratory column studies.
| References | Philippe Gombert, Stéphane Lafortune, Zbigniew Pokryszka, Elodie Lacroix, Philippe de Donato, et al.. Monitoring Scheme for the Detection of Hydrogen Leakage from a Deep Underground Storage. Part 2: Physico-Chemical Impacts of Hydrogen Injection into a Shallow Chalky Aquifer. Applied Sciences, 2021, 11 (6), pp.2686. 10.3390/app11062686. ineris-03266882 |
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| Country | France |
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