Soil-Gas Concentrations and Flux Monitoring at the Lacq-Rousse CO₂-Geological Storage Pilot Site (French Pyrenean Foreland): From Pre-Injection to Post-Injection

• Main Authors: Frédérick Gal, Zbigniew Pokryszka, Nadège Labat, Karine Michel, Stéphane Lafortune, André Marblé
• Format: Article
• Language: English
• Published: MDPI AG 2019-02-01
• Series: Applied Sciences
• Subjects: CO₂ storage; depleted gas field; soil-gas monitoring; baseline; injection; post-injection
• Online Access: https://www.mdpi.com/2076-3417/9/4/645
• ISSN: 2076-3417

Soil-gas concentrations and flux were measured during 20 separate measurement campaigns at the TOTAL Lacq-Rousse carbon capture and storage (CCS) pilot site, southern France, where 51,000 tons of CO₂ were injected in a depleted natural gas field. Baseline data (September 2008 to December 2009) are compared to monitoring data from the injection (March 2010 to March 2013) and post-injection (February 2014 to December 2015) periods. CO₂ soil-gas concentrations varied from atmospheric concentrations to more than 16% vol. with 1.4% as median value. Summer data showed high CO₂ concentrations in the soil that remained quite high during winter. Median CO₂ flux at the soil/atmosphere interface was close to 4.4 cm³·min^−1·m^−2. Carbon-isotope ratios measured on CO₂ in soil gas had a mean value of −23.5 ± 3.1‰, some deviation being due to atmospheric CO₂. Comparison between different gas species and the influence of temperature, pressure and soil-water content suggest that gases in near-surface environments are produced locally and naturally, and are unrelated to CO₂ ascending from the storage reservoir. Monitoring of CO₂ injection and the use of threshold levels is discussed as part of a practical approach considering specific regulations for the Lacq-Rousse CCS pilot experiment and constraints for the site operator.