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The establishment of a baseline of gases from an aquifer appears to be an essential prerequisite for monitoring and securing underground storage operations such as the storage of carbon dioxide (carbon capture and storage: CCS), methane or hydrogen. This study describes an innovative metrological technique dedicated to the in situ and continuous quantification of dissolved gases (CO2, O2, N2, CH4 and H2) in a shallow aquifer, on the site of Catenoy (Paris Basin) with a water table at a depth of 13 m. Monitoring was carried out from May 7, 2019 to November 19, 2019, before the simulation of H2 injection. Gases as vapors were collected from the aquifer through a nine-meter long, half-permeable polymer membrane positioned below a packer in a 25-meter deep well. Collected gases were analyzed simultaneously at the surface by fiber Raman (CO2, O2, N2, CH4 and H2) and infrared sensors (CO2). Gas concentrations were determined from Raman and infrared data, and then converted into dissolved concentrations using Henry's law. The dissolved gas concentrations were about constant over the 6 months period with average values of 31–40 mg L−1 (CO2), 8 mg L−1 (O2), 17 mg L−1 (N2), and 0 mg L−1 (H2, CH4) indicating a very low variability in the aquifer. This is believed to allow for rapid detection of any possible abnormal concentration variation, in particular linked to an accidental arrival of gases such as hydrogen. Such an online gas measurement system can be deployed as is on any site type of underground storage without any need for adaptation.

Since its construction, the St Bernard church of Lyon is the place of structural and geotechnical damage the origins of which are not clearly identified. The communication presents the results of a comprehensive monitoring of the structure over a period of 30 months allowing to shed some light on the reasons for such damage. The monitoring is also used as an alarm system for the community responsible for the church. The instrumentation should lead, in fine, to the definition of the most adequate answer to the problem of the future of this church.

Wells drilled through low-permeable caprock are potential connections between the CO2 storage reservoir and overlying sensitive targets like aquifers and targets located at the surface. The wellbore integrity can be compromised due to in situ operations, including drilling, completion, operations and abandonment or to geochemical degradation of the caprock-cement-casing system. We present here an experimental set-up in the underground rock laboratory of Mont-Terri (St Ursanne, canton of Jura, Switzerland): the drilling and well completion in the laboratory will be done in the aim of reconstructing interfaces between the caprock, the cement and the casing steel that would be close to the ones observed in situ. These well features will then be dipped within a CO2 stream, during a given time period before a final over-coring. Such an experiment should provide new insights on the quality of bounding between casing/cement/clay interfaces and its evolution due to geochemical reactions. In parallel, a modeling effort is performed focused on both geochemical and transport aspects of the interactions between the fluids and the well compartments.