continuous monitoring of dissolved gases (N, O, CO, H) prior to H injection in an aquifer (Catenoy, France) by on-site Raman and infrared spectroscopies: instrumental assessment and geochemical baseline establishment

• Published in: Analytical methods 2021-09, Vol.13 (34), p.386-382
• Main Authors: Lacroix, E, de Donato, Ph, Lafortune, S, Caumon, M.-C, Barres, O, Liu, X, Derrien, M, Piedevache, M
• Format: Article
• ISSN: 1759-9660; 1759-9679
• DOI: 10.1039/d1ay01063h

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 (CO 2 , O 2 , N 2 , CH 4 and H 2 ) 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 H 2 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 (CO 2 , O 2 , N 2 , CH 4 and H 2 ) and infrared sensors (CO 2 ). 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 (CO 2 ), 8 mg L −1 (O 2 ), 17 mg L −1 (N 2 ), and 0 mg L −1 (H 2 , CH 4 ) 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. An original monitoring system allowing in situ and continuous quantification of gases dissolved in an aquifer and combining Raman and infrared fiber sensors. The gas baseline was established before an experimental simulation of hydrogen injection.