Soil-Gas Concentrations and Flux Monitoring at the Lacq-Rousse CO<sub>2</sub>-Geological Storage Pilot Site (French Pyrenean Foreland): From Pre-Injection to Post-Injection
2019
Frédérick Gal | Zbigniew Pokryszka | Nadège Labat | Karine Michel | Stéphane Lafortune | André Marblé
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 CO<sub>2</sub> 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. CO<sub>2</sub> soil-gas concentrations varied from atmospheric concentrations to more than 16% vol. with 1.4% as median value. Summer data showed high CO<sub>2</sub> concentrations in the soil that remained quite high during winter. Median CO<sub>2</sub> flux at the soil/atmosphere interface was close to 4.4 cm<sup>3</sup>·min<sup>−1</sup>·m<sup>−2</sup>. Carbon-isotope ratios measured on CO<sub>2</sub> in soil gas had a mean value of −23.5 ± 3.1‰, some deviation being due to atmospheric CO<sub>2</sub>. 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 CO<sub>2</sub> ascending from the storage reservoir. Monitoring of CO<sub>2</sub> 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.
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