International audienceNear surface gas measurements are presented from a shallow (20 m depth) CO2 injection experiment at the CO2 Field Lab site in Svelvik, Norway, which was designed to test a variety of monitoring tools. Small areas of surface seepage of CO2 were detected during the experiment and these spread as the injection rate was increased. These features only accounted for a small fraction of the injected gas. Isotopic measurements revealed traces of injected CO2 at 50 cm depth nearer the injection point. The spatial extent of this is unknown but it is not likely to imply a significant amount of CO2 seepage. The locations of the gas escape were not as anticipated by prior modelling and highlight the difficulty of predicting where leakage may occur and, hence, where to deploy monitoring equipment. This unpredictability and the limited size of the seeps implies that monitoring will have to be flexible, preferably mobile and capable of detecting small features in large areas if successful leakage detection at surface is to be achieved. Low level seepage, such as that suggested isotopically here, could be significant for carbon auditing if it occurs over wide areas. This could be tested in areas of natural CO2 seepage

This study presents an overview of some results obtained within the French ANR (National Agency of Research) supported Géocarbone-Monitoring research program. The measurements were performed in Sainte-Marguerite, located in the French Massif Central. This site represents a natural laboratory for CO2/fluid/rock interactions studies, as well as CO2 migration mechanisms towards the surface. The CO2 leaking character of the studied area also allows to test and validate measurements methods and verifications for the future CO2 geological storage sites. During these surveys, we analyzed soil CO2 fluxes and concentrations. We sampled and analyzed soil gases, and gas from carbo-gaseous bubbling springs. A one-month continuous monitoring was also tested, to record the concentration of CO2 both in atmosphere and in the soil at a single point. We also developed a new methodology to collect soil gas samples for noble gas abundances and isotopic analyses, as well as carbon isotopic ratios. Our geochemical results, combined with structural geology, show that the leaking CO2 has a very deep origin, partially mantle derived. The gas rises rapidly along normal and strike-slip active faults. CO2 soil concentrations (also showing a mantle derived component) and CO2 fluxes are spatially variable, and reach high values. The recorded atmospheric CO2 is not very high, despite the important CO2 degassing throughout the whole area. Cette étude présente les principaux résultats de campagnes de monitoring géochimique menées en 2006 et 2007 dans le cadre du projet Géocarbone-Monitoring, sur le site de Sainte-Marguerite, situé dans le Massif Central. Ce site constitue un « laboratoire naturel » pour l’étude des interactions CO2/fluides/roches et des mécanismes de migration du CO2 vers la surface, à l’échelle des temps géologiques. Le caractère particulièrement émissif de cet « analogue » permet également de tester et valider des méthodes de mesure et de surveillance des futurs sites de stockage de CO2. Au cours des campagnes de terrain, nous avons analysé des flux de CO2 entre le sol et l’atmosphère, et nous avons prélevé et analysé à la fois des gaz des sols, et du gaz provenant de sources carbo-gazeuses, présentes dans toute la région. Un dispositif de « monitoring continu » dans le temps a également été testé, afin d’enregistrer conjointement les teneurs en CO2 de l’atmosphère et dans le sol en un point précis. Nous avons pu mettre au point un suivi géochimique basé sur la composition isotopique des gaz rares prélevés dans les sols. L’ensemble de nos résultats, confronté à la géologie de terrain, nous a permis de mettre en évidence l’origine mantellique du CO2. Ce CO2 remonte rapidement à la surface à l’état gazeux, le long de failles normales et/ou décrochantes, actives actuellement. Les teneurs et flux de CO2 dans le sol sont spatialement variables et élevés, et montrent également une origine mantellique. Les teneurs atmosphériques semblent faiblement augmenter par rapport à l’important dégazage observé dans la région.

The CO2 Field Lab project consisted in an injection of 1.7 tons of CO2 at a 20 m depth within a shallow aquifer located in fluvio-glacial deposits. Baseline acquisitions, leakage monitoring and post-injection monitoring were performed in the water phase at different depths (5, 10 and 15 m).Strong deviations of pH, specific conductance or alkalinity were observed and monitored at the horizons affected by the CO2 intrusion. The complex distribution of waters in the ridge deposits not only induced water/rock interactions but also mixing of saline and fresh waters. This points out the complexity of natural environments and the challenge in identifying CO2 leakage from deeper-seated reservoirs

International audienceNatural analogues studies have received growing interest during preceding years in a CCS perspective. There is a strong willing to deploy robust and reliable technologies to ensure the safety and integrity of CO2 underground storages. Here we present a dataset acquired in the Eifel volcanic district, using geochemical monitoring methods focussing on both dissolved and gaseous species. Onshore and offshore monitoring (Lake Laacher See) were performed to depict spatial behaviour of CO2 natural releases. Additional gaseous species, mainly helium and radon, were also monitored to better assess the shapes of gas vents, using methodologies that were learned from hydrological and tectonic applications. Lake water monitoring allowed the characterisation of the water body itself, in terms of lateral heterogeneities, to evaluate the impact of CO2 deep degassing near the bottom of the lake. The use of a dedicated sensor for monitoring in situ CO2 partial pressure did not provide more valuable information that was learned from more classical physico-chemical parameters. From those investigations, the usefulness of geochemical monitoring is still demonstrated, but the use of complementary approaches and methods is still needed to get a powerful set of techniques able to warn in case of leakages occurring from depth