Geochemical Study of Natural CO2 Emissions in the French Massif Central: How to Predict Origin, Processes and Evolution of CO2 Leakage

International audienceThis 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

La variabilit\ue9 g\ue9n\ue9tique des Caf\ue9iers spontan\ue9s de la section Mozambicoffea A. Chev. I. Pr\ue9cisions sur deux esp\ue8ces affines : Coffea pseudozanguebariae Bridson et C. sp. A Bridson

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Use of High-Resolution Satellite Imagery in an Integrated Model to Predict the Distribution of Shade Coffee Tree Hybrid Zones

In New Caledonia (21°S, 165°E), shade-grown coffee plantations were abandoned for economic reasons in the middle of the 20th century. Coffee species (Coffea arabica, C. canephora and C. liberica) were introduced from Africa in the late 19th century, they survived in the wild and spontaneously cross-hybridized. Coffee species were originally planted in native forest in association with leguminous trees (mostly introduced species) to improve their growth. Thus the canopy cover over rustic shade coffee plantations is heterogeneous with a majority of large crowns, attributed to leguminous trees. The aim of this study was to identify suitable areas for coffee inter-specific hybridization in New Caledonia using field based environmental parameters and remotely sensed predictors. Due to the complex structure of tropical vegetation, remote sensing imagery needs to be spatially accurate and to have the appropriate bands for monitoring vegetation cover. Quickbird panchromatic (black and white) imagery at 0.6 to 0.7 m spatial resolutions and multispectral imagery at 2.4 m spatial resolution were pansharpened and used for this study. The two most suitable remotely sensed indicators, canopy heterogeneity and tree crown size, were acquired by the sequential use of tree crown detection (neural network), image processing (such as textural analysis) and classification. All models were supervised and trained on learning data determined by human expertise. The final model has two remotely sensed indicators and three physical parameters based on the Digital Elevation Model: elevation, slope and water flow accumulation. Using these five predictive variables as inputs, two modelling methods, a decision tree and a neural network, were implemented. The decision tree, which showed 96.9% accuracy on the test set, revealed the involvement of ecological parameters in the hybridization of Coffea species. We showed that hybrid zones could be characterized by combinations of modalities, underlining the complexity of the environment concerned. For instance, forest heterogeneity and large crown size, steep slopes (N53.5%) and elevation between 194 and 429 m asl, are favourable factors for Coffea inter-specific hybridization. The application of the neural network on the whole area gave a predictive map that distinguished the most suitable areas by means of a nonlinear continuous indicator. The map provides a confidence level for each area. The most favourable areas were geographically localized, providing a clue for the detection and conservation of favourable areas for Coffea species neo-diversityJRC.G.2-Global security and crisis managemen

Supercritical Carbon Dioxide Bottoming Cycles for Off-Shore Applications—An Optimization Study

Closed Joule-Brayton thermodynamic cycles working with carbon dioxide in supercritical conditions (sCO(2)) are presently receiving great attention, for their multiple attractive aspects: high energy conversion efficiency, compact size, flexibility of operation, and integration with energy storage systems. These features make the sCO(2) technology interesting for several energy and industrial sectors, including renewable sources and waste heat recovery. A further promising area of application of sCO(2) systems is bottoming gas turbines in combined cycles installed in off-shore platforms, where the lack of space complicates the application of steam Rankine cycles. The use of steam implies large-scale components and demands for large space availability for the plant installation; in such context, the combination of gas turbines with sCO(2) cycles could open the way for developing novel combined cycles, which could be attractive for all the sectors which might take advantage from the footprint savings, the enhanced flexibility, and the fast dynamics of sCO(2) systems. In this work, we investigate the thermodynamic potential of combining sCO(2) cycles with an existing gas turbine for off-shore applications. We consider a midsize (25 MW) gas turbine available on the market and perform a series of thermodynamic optimizations of the sCO(2) bottoming cycle to maximize the exploitation of the heat discharged by the gas turbine. We analyze four alternative configurations and include realistic technical constraints, evaluated by leveraging on the most recent technical outcomes from ongoing sCO(2) research projects. A comparison is also proposed with a state-of-the-art steam Rankine cycle, in terms of system efficiency and footprint of the largest components. This study clarifies the advantages and challenges of applying sCO(2) in combination with gas turbines, and it confirms the relevance of sCO(2) systems for off-shore applications, calling for further technical studies in the field

Geochemical assessment of isolation performance during 10 years of CO 2 EOR at Weyburn

The Final-Phase Weyburn geochemical research program includes explicitly integrated yet conceptually distinct monitoring, modeling, and experimental components. The principal objectives are to monitor CO2-induced compositional evolution within the reservoir through time-lapse sampling and chemical analysis of produced fluids; to document the absence (or presence) of injected CO2 within reservoir overburden through analogous monitoring of shallow groundwater and soil gas; to predict intrareservoir CO2 migration paths, dynamic CO2 mass partitioning among distinct trapping mechanisms, and reservoir/seal permeability evolution through reactive transport modeling; to assess the impact of CO2-brine-rock reactions on fracture flow and isolation performance through experimental studies that directly support the monitoring and modeling work; and to exploit a novel stochastic inversion technique that enables explicit integration of these diverse monitoring data and forward models to improve reservoir characterization and long-term forecasts of isolation performance