HAL-BRGM, les publications scientifiques en libre accès du BRGM
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Monitoring the hydrothermal carbonization of biomass derived compounds by in-situ high-temperature-high-pressure Raman spectroscopy
No full textInternational audienceHydrothermal carbonization (HTC) is an energy efficient and sustainable method for converting biomass into carbon-based materials at low temperatures. However, the specific reaction conditions, involving the heating of feedstock in a confined environment under autogenous pressure, pose significant challenges for in-situ analytical techniques. To date, kinetic studies of HTC have primarily relied on ex-situ chemical analysis of samples collected during or after HTC runs. This study presents a novel approach utilizing continuous and rapid in-situ Raman spectroscopy to investigate the reaction progress in aqueous media, shedding light on the reaction pathways and kinetics of hydrothermal reactions. A custom-designed heated pressure vessel equipped with sapphire windows enabled the in-situ Raman monitoring of hydrothermal carbonization of biomass derivatives, such as glucose and xylose, under various experimental conditions including different heating rates and pressures. The results were compared with Raman data obtained ex-situ from a classical batch reactor at different reaction times. The in-situ measurements provided valuable insights into the composition of intermediates and products in both the liquid and solid phases simultaneously, yielding information that cannot be obtained through ex-situ analysis, such as the temperature of sugar decomposition and carbon precipitation depending on the nature of the sugar, the heating rate or the pressure
Evaluating migration hazard for recently remobilized managed coastal dunes
No full textInternational audienceSparsely vegetated or unvegetated coastal dunes are inherently dynamic, regardless of their size (Hesp et al., 2022). A salient characteristic of these dunes is their landward migration, driven by prevailing onshore winds, at rates that can exceed several meters per year. The rapid evolution of freely evolving coastal dunes inevitably raises concerns about the burial of infrastructure and more generally, the back dune areas. In a context where dune system remobilization is emerging as a nature-based management solution with multiple benefits (ecological reconnection, chronic marine erosion and sea-level rise effects mitigation), precise, spatially explicit quantitative assessments of dune migration hazards are essential. This is more critical given the trends of increasing urbanization and the concentration of socio-economic interests in coastal zones.Along the 230 km of the Aquitaine coast (southwest France), coastal dunes, which landscape is largely inherited from nearly two centuries of management, stabilization, and episodic mechanical re-profiling, have undergone spontaneous remobilization over the past decade (Nicolae Lerma et al., accepted). Across extensive sectors, dunes have transitioned from geometrically fixed, vegetated forms to aerodynamic, transgressive dunes (Figure 1a). This shift presents both opportunities and challenges for short- and long-term management strategies but also raises critical questions about accommodating rapid migration rates and evolving dune morphology. Current approaches to assessing burial hazards often overlook key parameters, such as interannual wind variability, climate change-induced trends in forcing, dune and back-dune morphology, and sediment budgets. Furthermore, methods relying on historical migration rates are inapplicable in regions where dunes were artificially stabilized during the 20th century through management interventions.Using annual airborne LiDAR data (Figure 1b.) and simulations with the morphodynamic model DUNA (Kombiadou et al., 2023, Figure 1c.), we analyze the factors influencing the migration speed of recently unvegetated dunes. We also investigate the impact of hybrid management strategies (designed to either accelerate or mitigate dune remobilization) at large spatial scales (hundreds of meters to tens of kilometers)
Reassessment of DLVO theory at sub-nanometric scale: Application to Na-smectite
No full textInternational audienceThe nearly century-old DLVO (Derjaguin, Landau, Verview, and Overbeek) theory decomposes the interaction forces between solid surfaces separated by a fluid into attractive and repulsive components. In its standard version, it applies beyond solid surface separation distances of around 1 nm. For sub-nanometer distances, additional so-called hydration forces were widely invoked to explain the discrepancy between theory and measurements. Alternatively to this semi-empirical approach, either the validity of the theoretical expression for the electrostatic component of the disjoining pressure, or the adaptation of the Boltzmann distribution usually considered in the application of DLVO theory are questioned. Here, it is suggested that the introduction of a hydration component whose parameters cannot be predetermined but are a matter of calibration is unnecessary. Hydration effects, introduced in the calculation of ionic concentrations, directly influence ions distributions and therefore the repulsion of adjacent electric double layers. This effect is thus part of the electrostatic component of the disjoining pressure. An analytical expression extending DLVO theory to small surface separation distances together with a simplified electrical model, both proposed here, enable reproducing data for Na-smectite. Results are also in good agreement with thermodynamic and molecular dynamics calculations. It is confirmed that the discrepancy between theory and observations is mainly due to the underestimation of counterions concentration at the mid-plane identified using an inappropriate electrical model. For ions with radii around 0.1 nm, commonly found in natural media, the standard DLVO expression can still be used, but with mid-plane concentrations calculated using an appropriate electrical mode
La base de données SIGREF (SItes du Gravettien REcent et Final). Chroniques de la construction collective d'un jeu de données pluridisciplinaire
No full textNational audienceCe poster est l’occasion de présenter la démarche pluridisciplinaire mise en place dans le cadre du Projet Collectif de Recherche « Quel Gravettien en Nouvelle-Aquitaine ? ». Ce dernier a pour principal objectif de questionner la sériation de la fin du Gravettien en France par une approche critique multi-proxy. Nous avons ainsi créé une base de données spécifique : SIGREF. Celle-ci a pour vocation de 1) recueillir l’ensemble des données publiées et produites dans le cadre du projet, pour les séries du Gravettien récent et final en Nouvelle-Aquitaine, 2) disposer d'un outil de travail qui permettra de questionner la sériation de la fin du Gravettien en croisant différents proxys par le biais de requêtes, 3) valoriser et rendre disponible la structure de la base tout autant que les données qui la nourrissent.Nous présentons ici le modèle conceptuel de SIGREF, comprenant une documentation des champs et relations entre tables de la base. Afin de tester la robustesse de notre modèle, nous définissons 10 user-cases qui sont des requêtes génériques pré-codées dans la base, que nous avons appliqués à « Frankenstein », un jeu de données imaginaires inspiré des expériences des membres du projet
One water? In pursuit of water circularity in Moroccan Oases
No full textSource Agritrop Cirad (https://agritrop.cirad.fr/616736/) * Autres projets (id;sigle;titre): ;MASSIRE;(ITA) Innovations rurales et eau dans les territoires sud du Maghreb//International audienceWater resources development and the intensification of water uses have profoundly altered water circulation in the arid river basins of southeast Morocco, leading to water reallocation and scarcity. Four case studies show how the State and farmers are adapting, often unsustainably, to the created water scarcity, including by promoting local water circularity. This paper argues that incorporating the principles of the circular economy 'Reduce' and 'Replenish' might be helpful to reconnect surface and groundwater at the explicit condition to reduce anthropogenic pressure on water resources and consider water circulation at the basin level
Metal transport by magmatic volatile phases in crustal systems
No full textInternational audienceMagmatic volatile phases (MVPs) are multicomponent fluids that are a transport medium for metals being transferred from deep magmatic sources to sites of ore formation. However, the melt-to-fluid exchange of metals remains elusive because existing empirical simulations primarily address metal transport through the fate of one chemical element. We use a comprehensive thermochemical model to simulate the fractional crystallization of a silicate melt that degasses a multicomponent MVP. We show that the major and trace element abundances in MVPs formed from non-enriched magmatic systems are indistinguishable from MVPs found as fluid inclusions in mineralized and non-mineralized systems. We therefore conclude that ore formation is the consequence of repetitive intrusion-fractionation-degassing cycles common to crustal systems without pre-enriched sources, as opposed to scenarios wherein a particular or complex chemical system is required. Instead, the driving force of ore formation is a long-lived system fueled by an H2O- and Cl-bearing melt. Variations in metal signatures of fluids therefore reflect the pressure-temperature path of melt ascent and the changes in major element composition of the melt
Lithium Isotopic Composition of Fluid Inclusions provides insights into Fluid–Rock Interaction in Subducted Sediments and Sources of Mud Volcano Fluids
No full textInternational audienceLithium isotopes have been widely used to investigate fluid-mediated processes in subduction.However, direct analysis of pore fluids in metamorphic rocks remains challenging due to prohibitive depths at which these processes occur. To evaluate the potential of Li concentration and isotopic composition recorded in fluid inclusions, we employed a crush-leach technique to +9.5‰), and Shimanto (+2.5‰ to +10.4‰) is primarily governed by the presence of Li-bearing mineral phases during vein formation-particularly chlorite, white mica, and paragonite-and their capacity to retain lithium. In closed systems, δ 7 Li values of pore fluids can be explained by Rayleigh fractionation during the crystallization of chlorite, illite/phengite, and paragonite, which dominantly incorporate 6 Li, leaving the fluids enriched in 7 Li and therefore having heavier δ 7 Li values. Conversely, in open systems, continuous Li removal from the rocks results in decreasing δ 7 Li values of pore fluids, though their Li concentrations remain comparable to those in closed systems. Similarities in Li concentrations and δ 7 Li values between leachates and mud volcano fluids in modern examples of subduction zone forearcs further confirm that such fluids dominantly originate from subducted sediments. Collectively, this study demonstrates the capability of Li isotope systematics of fluid inclusions to effectively contribute to the understanding of fluid-rock interactions in subducted lithologies.</div
Assessment of Well Integrity for Repurposing O&G Wells for CO <sub>2</sub> Storage─Essential Safety Considerations
No full textInternational audienceWells that develop leaks due to integrity issues can pose serious risks to both the environment and human health, particularly if they release previously captured CO 2 back into the atmosphere or contaminate freshwater aquifers. Ensuring reliable underground storage, therefore, presents a significant challenge in well integrity. The injected CO 2 can lead to substantial corrosion of metal materials and cement within the well. Moreover, the quality of cementation may deteriorate due to improper cement placement or changes in its mechanical properties arising from the well's operational activities. Identifying, quantifying, and mitigating this corrosion, along with assessing cementation quality, are pivotal for maintaining satisfactory well conditions. This study proposes solutions, through a literature review, that focus on material selection and the composition of CO 2 flow. It emphasizes essential considerations for a preliminary evaluation of both active and suspended wells for their reuse in CO 2 injection and storage in CCS operations. Conducting a systematic literature review has been crucial in identifying the key factors for assessing wells suitability for CO 2 injection. The outcome is a flowchart designed for evaluating active and suspended wells, encompassing a qualitative and initial analysis of critical factors such as cement integrity, corrosion, CO 2 flow composition, and material compatibility. If the recommended actions do not resolve the issues with a well, it should be plugged and abandoned
Polyphase tectonic, thermal and burial history of the Vocontian basin revealed by U–Pb calcite dating
No full textInternational audienceThe Vocontian Basin in southeastern France records a long-lived history of subsidence and polyphase deformation at the junction of Alpine and Pyrenean orogenic systems. This study aims to reconstruct the tectonic, burial and thermal evolution of this basin, based on new U-Pb dating of calcite from veins and faults combined with new RSCM (Raman Spectroscopy of Carbonaceous Material) thermometry and stratigraphy-based burial models. Three main generations of calcite are identified: (1) the Late Cretaceous to Paleocene period related to the Pyrenean-Provençal convergence (∼ 84-50 Ma); (2) the Oligocene period linked to the extension of the West European Rift (∼ 30-24 Ma); and (3) the Miocene period, ascribed to strike-slip and compression associated with the Alpine collision (∼ 12-7 Ma). No older ages related to the Jurassic and Early Cretaceous rifting phase are obtained, despite targeted sampling near normal faults, suggesting highly localized syn-rift fluid circulation or dissolution of early calcite mineralization during subsequent tectonic events. RSCM data highlight a pronounced east-west thermal gradient. Peak temperatures are below 100 °C in the west and exceed 250 °C in the eastern basin, reflecting greater crustal thinning and salt diapirism in the eastern Vocontian Basin with the overlapping Jurassic and Cretaceous rifting phases. These results emphasize the significant impact of the West European Rift in southeastern France. They further highlight the potential mismatch between large-scale tectonic processes and the tectonic history inferred from calcite U-Pb dating, which is sensitive to the presence of fluids and the physical conditions required for their preservation
The multiple dimensions of geodiversity
No full textInternational audienceFor two decades, the concept of geodiversity has gained a prominent interest within a broad scientific community spanning multiple disciplines. The expansion of this concept has led to a multitude of definitions, approaches, renewed conceptualizations and neologisms (e.g. geosites, geoheritage, geoconservation, geotourism, geodiversification, geofunctionality, megageodiversity, exogeodiversity, geodiversity hotspots). Based on the existing literature, this Perspective has the objective to highlight and structure the idea that geodiversity is a multidimensional concept prone to operationalization. Contrary to usual definitions, we argue here that geodiversity should not be considered purely abiotic as it is also shaped by biotic and anthropic factors within the Earth's Critical Zone: it represents a four-dimensional open system characterized by multiple and complex interactions with the biosphere and the anthroposphere, that must be understood to achieve sustainability