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The East African Rift (EAR) is a large opening system that allows the observation of all stages of rift evolution from continental opening in the south to oceanization in the north (Ethiopia-Djibouti). Also, the Asal–Ghoubbet active rift, in the Republic of Djibouti, is composed of a magmatic crust and tends to evolve into an oceanic crust. It’s a site of interest for geothermal energy and natural hydrogen. Previous studies have indicated that dihydrogen (H2) emanates from this rift. However, the well-known serpentinization reaction is not the mechanism generating H2 at this site. Rather, the H2 is generated as follows: (1) by alteration of basaltic lava at depth via reaction with seawater flowing from Ghoubbet Bay towards Lake Asal; (2) by simple degassing of the volcanic chamber located a few kilometers below the Fiale Caldera in the rift axis; or (3) as a result of pyritization processes via the oxidation of H2S.Drill cuttings from the Fiale 1 (F1) and Gale le Goma 1 (Glc1) geothermal wells (located on the inner and outer rift margins, respectively) were analyzed to determine where H2 is generated. Total rock analyses indicated distinct zones at depths of 464 m and 280 m for F1 and Glc1, respectively, representing the boundary between the Asal and Stratoïd Basalts. 57Fe Mössbauer analyses show a decrease in the percentage of Fe3+ at depth, indicating that Fe2+-rich material, particularly in the Stratoïd Basalts, may be a source of H2.Based on well data from the rift center and the outer rift margin, it is evident that H2 is present at the surface in the rift axis and that this area offers good remnant potential because of the presence of Fe-rich chlorite. Conversely, few H2 emissions were measured at the surface on the outer rift margins, although well data showed some H2 (~0.25%) at depth. The presence of a cap rock in the rift axis has not yet been proven; however, the high loss on ignition and the mineralogy in well Glc1 may indicate that the rocks are sufficiently altered to offer potential as a seal. If so, the rift margins would offer greater exploration potential than the rift center.

The Asal–Ghoubbet active rift in the Republic of Djibouti is a site of interest for geothermal energy and natural hydrogen, and previous studies have indicated that dihydrogen (H2) emanates from this rift. However, the well-known serpentinization reaction does not appear to be the main mechanism generating H2 at this site. Rather, the H2 is generated as follows: (1) by alteration of basaltic lava at depth via reaction with seawater flowing from Ghoubbet Bay towards Lake Asal; (2) by simple degassing of the volcanic chamber located a few kilometers below the Fiale Caldera in the rift axis; or (3) as a result of pyritization processes via the oxidation of H2S. Analysis of microorganisms did not indicate any production or consumption of H2, CO2, or CH4; therefore, it is unlikely that microorganisms affected H2 gas contents measured at the surface. However, air contamination at fumaroles is typically considerable and may limit interpretation of such processes. Drill cuttings from the Fiale 1 (F1) and Gale le Goma 1 (Glc1) wells (located on the inner and outer rift margins, respectively) were analyzed to determine where H2 is generated. Total rock analyses indicated distinct zones at depths of 464 m and 280 m for F1 and Glc1, respectively, representing the boundary between the Asal and Stratoïd Basalts. 57Fe Mössbauer analyses show a decrease in the percentage of Fe3+ at depth, indicating that Fe2+-rich material, particularly in the Stratoïd Basalts, may be a source of H2. Based on well data from the rift center and the outer rift margin, it is evident that H2 is present at the surface in the rift axis and that this area offers good remnant potential because of the presence of Fe-rich chlorite. Conversely, few H2 emissions were measured at the surface on the outer rift margins, although well data showed some H2 (~0.25%) at depth. The presence of a cap rock in the rift axis has not yet been proven; however, the high loss on ignition and the mineralogy in well Glc1 may indicate that the rocks are sufficiently altered to offer potential as a seal. If so, the rift margins would offer greater exploration potential than the rift center.

International audience

Dihydrogen (H2) is generated by fluid–rock interactions along mid-ocean ridges (MORs) and was not, until recently, considered as a resource. However, in the context of worldwide efforts to decarbonize the energy mix, clean hydrogen is now highly sought after, and the production of natural H2 is considered to be a powerful alternative to electrolysis. The Afar Rift System has many geological features in common with MORs and offers potential in terms of natural H2 resources. Here, we present data acquired during initial exploration in this region. H2 contents in soil and within fumaroles were measured along a 200 km section across the Asal–Ghoubbet rift and the various intervening grabens, extending from Obock to Lake Abhe. These newly acquired data have been synthesized with existing data, including those from the geothermal prospect area of the Asal–Ghoubbet rift zone. Our results demonstrate that basalt alteration with oxidation of iron-rich facies and simultaneous reduction in water is the likely the source of the hydrogen, although H2S reduction cannot be ruled out. However, H2 volumes at the surface within fumaroles were found to be low, reaching only a few percent. These values are considerably lower than those found in MORs. This discrepancy may be attributed to bias introduced by surface sampling; for example, microorganisms may be preferentially consuming H2 near the surface in this environment. However, the low H2 generation rates found in the study area could also be due to a lack of reactants, such as fayalite (i.e., owing to the presence of low-olivine basalts with predominantly magnesian olivines), or to the limited volume and slow circulation of water. In future, access to additional subsurface data acquired through the ongoing geothermal drilling campaign will bring new insight to help answer these questions.

Natural hydrogen seeps called fairy circles have been identified in Mali, Brazil, Russia, and United-States. Natural hydrogen is produced from a field in Mali for 7 years. The natural hydrogen system is still poorly understood and needs to be studied in new geological contexts as to streamline hypotheses on the system dynamics and elements into concepts. In Australia, numerous circular surface features, commonly called salt lakes or swaps, are visible from the sky but no existing work shows nor quantifies any hydrogen content in those features. In this study, we reviewed the existing literature on fairy circles as to determine and directly test with soil-gas measurements if hydrogen surface-emitting features are present in Australia. We determined best candidates to test with a multi-disciplinary approach linking geology, multi-physical imaging, and seismic interpretation. Soil-gas measurements showed persistent hydrogen concentration localized in the external ring of circular depressions aligned along the Darling Fault, a major crustal boundary between the granitic, mafic and ultramafic rocks of the Yilgarn Craton from the sedimentary rocks of the Perth Basin. This work is the proof that fairy circles, in the meaning of H2 emitting structures, are present in Australia and opens the door to new prospectivity pathways by evaluating original hypotheses on natural hydrogen generation, migration pathways and entrapment. This geological setting promotes deep serpentinization of ultramafic rocks as well as oxidation of iron-rich Archean rocks and mafic dikes as potential hydrogen sources that are both of massive potential economic value. This hydrogen can circulate and be entrapped as aqueous hydrogen in low-salinity aquifers or migrate in gaseous phase in fault zones up to intermediate structural reservoir or to the surface.

International audience; The ophiolite of Sivas (Turkey) was studied in order to define the chronology of different alteration events related to a series of serpentinization and carbonation episodes. Six samples were investigated, representative of different types of ophicalcite (partially carbonated serpentinite). X-ray diffraction (XRD) and Mössbauer spectroscopy were used to determine the bulk mineralogy and the bulk Fe 3+ /Fe tot ratio, respectively. Electron microprobe and secondary ion mass spectrometer (SIMS) analyses were also conducted to identify the chemical composition of different mineral phases in addition to the carbon and oxygen isotopic compositions of calcite. An initial, i.e. pre-obduction, phase of olivine and pyroxene serpentinization was followed by a brecciation event associated with precipitation of massive serpentine. This first alteration event occurred during exhumation of the peridotites to the seafloor, followed by a carbonation event at temperatures in the range 35‒100 °C. A low-temperature (∼35 °C) carbonation event occurred between 90 and 65 Ma. Finally, a reheating of the system likely occurred after the obduction at 55‒40 Ma, resulting in a carbonation episode followed by late serpentinization. Our study presents the first direct evidence of serpentinization after obduction. In that geological context, the hydrogen produced during the proposed multiphase serpentinization may have been trapped by the salt deposits overlying the ophiolite but subsurface data will be necessary to define potential traps and reservoirs; further studies are also needed to determine whether the serpentinization process is still ongoing.; L’ophiolite de Sivas (Turquie) a été étudiée pour caractériser les différents épisodes de serpentinisation et de carbonatation. Pour cela, six échantillons représentatifs des différents types d’ophicalcite (serpentinite partiellement carbonatée) ont été analysés. La diffraction des rayons X et la spectroscopie Mössbauer ont été utilisées pour déterminer respectivement la minéralogie et le rapport Fe 3+ /Fe tot en roche totale. Les analyses en microsonde électronique et au spectromètre de masse à ions secondaires ont permis d’identifier la composition chimique des différentes phases et la signature isotopique en carbone et en oxygène des calcites. Ces mesures ont permis de proposer un modèle où l’olivine et le pyroxène ont été serpentinisés avant de subir une bréchification menant à la précipitation de serpentine massive dans les fractures. Ce premier épisode d’altération a eu lieu durant l’exhumation des péridotites, suivie par une carbonatation entre 35 °C et 100 °C. Une autre carbonatation basse température (∼35 °C) a ensuite eu lieu entre 90 et 65 Ma. Enfin, un réchauffement du système a probablement eu lieu après obduction entre 55 et 40 Ma menant à une carbonatation et une serpentinisation tardive. C’est ainsi la première évidence directe de serpentinisation post-obduction. Il n’est pas clair si l’hydrogène produit durant les différents épisodes de serpentinisation a été piégé par les dépôts de sel sus-jacents et d’autres études seront nécessaires pour comprendre si la serpentinisation est toujours en cours.

Hydrogen escaping from sedimentary basins has already been described in various parts of the world. Some of these leakages have been identified by superficial circular depressions, also called “fairy circles”. Gas detection measurements, randomly repeated after a few months have shown that the amount of hydrogen present in soils is not constant neither versus time nor versus position in a given structure. Permanent monitoring gas analyzers were installed in the ground to estimate hydrogen flow outgassing from a topographical circular depression located in Brazil. Data show that a hydrogen flux occurs during the hottest moment of the day, as shown with permanent sensors set at a regular spacing. The process may look like a soil evaporation. In that same structure, other detectors show much higher and irregular gas output which present an unclear correlation as a function of ambient temperature and atmospheric pressure. The relationship with temperature suggests a role of water saturation driving the overall hydrogen fluxes. The reported geochemical data imply that (1) one measurement taken at a given hour on a structure cannot be considered as quantitative, as it varies too much with time and is also probably related to the soil perturbation induced by the shallow drilling, (2) hydrogen released through the soils of the studied structure is recharged daily, (3) hydrogen flux is high enough to reach the surface without being buffered by water or bacterial activity within the soil and (4) soil cannot be solely considered as a hydrogen sink but also, at least in some areas, as a hydrogen emitter. This appears to highlight that the subsurface may be considered in this site as a source of natural hydrogen, clearly differentiated from a biochemical system of atmospheric H2 consumed by bacteria.

Deeply buried sandstone reservoirs are targeted in the Upper Rhine Graben (URG) for geothermal and hydrocarbon resources. These reservoirs are affected by a convective heat flow along fault zones and have a complex diagenetic and deformation history recorded in their paragenetic sequence. Here, the focus is made on siderite and barite cementation characterisation, which trace paleo geothermal circulations within the fracture network affecting the Buntsandstein Gp. sandstones. A double approach on geochemistry and fracture network features is used to characterise fluid-flow episodes in the rift basin and on its shoulders. Barite sulphur isotopic signature suggests a common source for all the locations. However, Rare Earth Elements distribution patterns, oxygen isotopic ratios, and fluid inclusion study suggest two distinct flow regimes for fluids associated with barite precipitation along the shoulders and at depth in the middle of the graben. The barite has a higher content in total REE and contains non-saline fluid inclusions on the graben shoulders, suggesting that fluid circulations within the border faults interact with sulphate rich layers and precipitate at temperature above 150 °C. In deep-seated samples from the central part of the basin, barite fluid inclusions show a wide range of salinities, suggesting a higher contribution of sedimentary brines and precipitation at lower temperatures (

In many basins, hydrogen-emitting structures are now observed, but the estimation of the H2 flow leading to their formation remains poorly constrained since all data show that the H2 emissions are variable in space and time. We present here the data of a long-term monitoring campaign with a high density of permanent hydrogen detectors installed in 2 structures in the Minas Gerais State (Brazil). Results show that two kinds of signals are recorded, large sporadic pulses that affect the H2 content of the soil for one or two days and smaller ones, with a daily periodicity, that last 6 h and during which the near surface soil concentration usually does not exceed 200 ppm. This last signal is very regular in frequency, less in amount, and the daily maximum happens around noon or in the early afternoon. We interpret the large pulses as evidences of a deep hydrogen flux, leaking either from a reservoir located in the subsurface, from an aquifer which is degassing or, although it seems unlikely, directly from the H2 generation area. The time correlation between the pulse and the increase of the daily signal suggests that this last one corresponds to the slow release of the gas that has been captured by the soil during its transport towards the surface. This daily signal is most likely influenced by external factors such as atmospheric pressure and sub-surface bacterial activity. In map view, the lack of correlation between the highest hydrogen concentrations over time suggests that the soil is very heterogeneous and that preferential pathways exist. The results confirm that long-term monitoring, over a few months, is mandatory to catch a certain number of high pulses and so to have a better estimation of the real flow. Data also suggests that sensors with a large concentration range should be used (from 10 to several 104 ppm). Even if quantification of leakage doesn't help to quantify the subsurface reserves, these new data allow a more precise evaluation of the quantity of H2 released in surface by these structures, few hundred of kilo per day, and confirm the high H2 prospectivity of this basin.

International audience

National audience; Les territoires multiplient leurs efforts pour atteindre les objectifs de la loi de transition énergétique pour la croissance verte, parmi lesquels figure la nécessité de porter la part des énergies renouvelables à 32 % de la consommation finale brute d’énergie en 2030. Cet article vise à recenser les risques industriels et environnementaux liés à l’émergence à la fois de nouveaux acteurs impliqués dans le déploiement des énergies renouvelables et de nouveaux matériaux et technologies. Associées à ces risques, des solutions techniques et organisationnelles sont proposées pour les maîtriser et tenter de faire de la transition une opportunité pour les territoires.

The back arc extensional area of Tuscany is characterized by anomalously high heat flow as a result of lithospheric thinning facilitated by locally intruded granite, which ultimately led to the occurrence of numerous fumaroles and other manifestations of geothermal activity. The present study builds up on molecular and isotopic geochemical analyses of fumarolic gases discharging near Larderello geothermal field in order to report on their origin and generation mechanisms. The fumarole gases are rich in CO2 (15.65–92.5 vol%), poor in CH4 (0.08–3.70 vol%) and highly-depleted in C2+ ( −4.2‰VPDB) reflect thermo-metamorphic of CO2, however magmatic-volcanic contribution cannot be ruled out. This work tests various hypotheses of the origin of H2: the intruded granite, the ophiolite and/or a deeper source. Petrographic and electron microbeam investigations performed on the Ligurian ophiolite and plutonic granite, which outcrops in the vicinity of the study area, revealed serpentinization of ophiolite (in contact with geothermal fluids at 200 °C) as the most probable source of the measured H2. Hydrogen that forms deeper, potentially near or within the granitic intrusion, at higher temperatures, is likely consumed to form abiotic methane.

The source rock characteristics (e.g. thickness, lateral extension, richness) are known to be highly variable in both time and space. The Lower Jurassic formations of north-western Europe contain source rocks with organic-rich intervals showing different characteristics from one region to another: the Paris Basin differs from the South-East Basin of France, but organic content and hydrogen index also vary within a single basin. During the Early Jurassic, the overall depositional environment of north-western Europe corresponded to an epicontinental domain at the western extremity of the Tethys Ocean. The early transgressive phase of the Jurassic induced flooding of this European realm. Because of the evolution of the connections and threshold of the European basins and their associated sedimentary settings, this domain occupied a key position for the deposition of organic-rich layers. Using a forward modelling approach, we aim to predict the heterogeneous characteristics of such sediments. It is widely accepted that primary productivity and preservation are key factors favouring the accumulation of organic-rich layers. However, the roles of these factors remain to be assessed and the processes leading to accumulation and preservation need to be quantified. We focus on the Lower Jurassic (Hettangian to Toarcian) in France, since this provides a vast amount of data to calibrate the 100-kyr time step model in terms of an accurate framework including paleogeography, stratigraphy, lithology, palaeontology, mineralogy and geochemistry. Results show that favourable conditions for the deposition of organic-rich sediment can occur even with moderate primary productivity and without requiring anoxic conditions. These windows are firstly dependent on internal factors directly linked to the basin morphology, such as sedimentation rate, bathymetry and distance from the coastline. We do not need to evoke external factors such as oceanic anoxic events or enhancement of primary production to account for the deposition of organic-rich sediments.

International audience; Sandy kaolinite-rich soils, collected in a H2-emitting circular depression (ca. 500 m in diameter), located in the São Francisco basin (Brazil), were exposed to H2 gas concentrations in the 500–5000 ppm range for up to eight weeks. The samples were found to consume H2 at a rate of approximately 0.05–0.1 mmol H2/soil kg/day due to the microbial activity. DNA extraction from these soil samples before and after H2 exposure, followed by Ribosomal Intergenic Spacer Analysis (RISA) and 16S rRNA gene amplicon sequencing, indicated that (i) the bacterial community is dominated by phyla that have been previously recognized to scavenge atmospheric H2, and (ii) H2 exposure leads to a significant modification of the bacterial community distribution. Measured H2 uptake rates were fitted to the integrated form of the Michaelis-Menten equation and were further implemented in a 1-D reactive transport model. The model simulates gas-soil interactions in a 1-m vertical soil column, assuming homogeneous distribution of H2-consuming bacteria. The evolution of the H2 concentration in the unsaturated soil porosity along the column was simulated considering two different scenarios: a deep H2 source (Case 1) and a biogenic surface source (Case 2). It was shown that, in the case of diffusion-dominated H2-transport as considered in this study, bacterial activity will control the amplitude of the H2 flux across the column. Moreover, we determined that bacterial activity can dramatically decrease the H2 concentration in the soil porosity, by a factor of two compared to the source concentration. According to the simulation, the time-resolved concentration data collected in the São Francisco depression [Prinzhofer et al., 2019; International Journal of Hydrogen Energy] are consistent with the combination of a deep (Case 1) and a surficial biogenic (Case 2) H2 source in this locality

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The active debate about the processes governing the organic-rich sediment deposition generally involves the relative roles of elevated primary productivity and enhanced preservation related to anoxia. However, other less spotlighted factors could have a strong impact on such deposits, e.g., residence time into the water column (bathymetry), sedimentation rate, transport behavior of organo-mineral floccules on the sea floor. They are all strongly interrelated and may be obscured in the current conceptual models inspired from most representative modern analogues (i.e., upwelling zones and stratified basins). To improve our comprehension of organic matter distribution and heterogeneities, we conducted a sensitivity analysis on the processes involved in organic matter production and preservation that have been simulated within a 3D stratigraphic forward model. The Lower-Middle Toarcian of the Paris Basin was chosen as a case study as it represents one of the best documented example of marine organic matter accumulation. The relative influence of the critical parameters (bathymetry, diffusive transport, oxygen mixing rate and primary production) on the output parameters (Total Organic Carbon, and oxygen level), determined performing a Global Sensitivity Analysis, shows that, in the context of a shallow epicontinental basin, a moderate primary productivity (&gt, 175 gC&middot, m&minus, 2&middot, year&minus, 1) can led to local anoxia and organic matter accumulation. We argue that, regarding all the processes involved, the presence and distribution of organic-rich intervals is linked as a first-order parameter to the morphology of the basin (e.g., ramp slope, bottom topography). These interpretations are supported by very specific ranges of critical parameters that allowed to obtain output parameter values in accordance with the data. This quantitative approach and its conclusions open new perspectives about the understanding of global distribution and preservation of organic-rich sediments.

The Paleozoic intracratonic North African Platform is characterized by an association of arches (ridges, domes, swells or paleo-highs) and low subsidence rate syncline basins of different wavelengths (75–620 km). The structural framework of the platform results from the accretion of Archean and Proterozoic terranes during the Pan-African orogeny (750–580 Ma). The Ahnet and Mouydir basins are successively delimited from east to west by the Amguid El Biod, Arak-Foum Belrem, and Azzel Matti arches, bounded by inherited Precambrian sub-vertical fault systems which were repeatedly reactivated or inverted during the Paleozoic. Major unconformities are related to several tectonic events such as the Cambrian–Ordovician extension, Ordovician–Silurian glacial rebound, Silurian–Devonian “Caledonian” extension/compression, late Devonian extension/compression, and “Hercynian” compression. The deposits associated with these arches and syncline basins exhibit thickness variations and facies changes ranging from continental to marine environments. The arches are characterized by thin amalgamated deposits with condensed and erosional surfaces, whereas the syncline basins exhibit thicker and well-preserved successions. In addition, the vertical facies succession evolves from thin Silurian to Givetian deposits into thick Upper Devonian sediments. Synsedimentary deformations are evidenced by wedges, truncations, and divergent onlaps. Locally, deformation is characterized by near-vertical planar normal faults responsible for horst and graben structuring associated with folding during the Cambrian–Ordovician–Silurian period. These structures may have been inverted or activated during the Devonian compression and the Carboniferous. The sedimentary infilling pattern and the nature of deformation result from the slow Paleozoic reactivation of Precambrian terranes bounded by vertical lithospheric fault zones. Alternating periods of tectonic quiescence and low-rate subsidence acceleration associated with extension and local inversion tectonics correspond to a succession of Paleozoic geodynamic events (i.e. far-field orogenic belt, glaciation).

International audience; The understanding of fluid flow in faulted sandstones is based on a wide range of techniques. These depend on the multi-method determination of petrological and structural features, porous network properties and both spatial and temporal variations and interactions of these features. The question of the multi-parameter analysis on fluid flow controlling properties is addressed for an outcrop damage zone in the hanging wall of a normal fault zone on the western border of the Upper Rhine Graben, affecting the Buntsandstein Group (Early Triassic). Diagenetic processes may alter the original pore type and geometry in fractured and faulted sandstones. Therefore, these may control the ultimate porosity and permeability of the damage zone. The classical model of evolution of hydraulic properties with distance from the major fault core is nuanced here. The hydraulic behavior of the rock media is better described by a pluri-scale model including: 1) The grain scale, where the hydraulic properties are controlled by sedimentary features, the distance from the fracture, and the impact of diagenetic processes. These result in the ultimate porous network characteristics observed. 2) A larger scale, where the structural position and characteristics (density, connectivity) of the fracture corridors are strongly correlated with both geo-mechanical and hydraulic properties within the damage zone.

International audience; Middle Pleistocene Gilbert-type delta in the Gulf of Corinth, Greece, has been investigated combining field methods and photo acquisition by drone to generate a high-resolution 3D model. This study case can be used to document four different dynamics in Gilbert-type bottomset deposits, each one of which is characterized by a specific range of facies, facies associations and geometries: (1) the sandy-gravelly bottomset, (2) the erosional-bypass stage, (3) the fine-grained bottomset and (4) the massive-sandy bottomset. By comparing the typologies of the bottomset, we propose a conceptual model that predicts the occurrence of these four different bottomset stage dynamics depending on the stratigraphic context.During highstand normal regression, the gravelly bottomset develops under subcritical flow. The supercritical flow undergoes a stationary hydraulic jump in the toeset due to the slope break. As a result, a low-relief channel-levees system is formed in the bottomset. The channels are filled/reworked by backstepping conglomeratic lenses interbedded with silty concave-up and concave-down levees. During normal regression, the foreset beds are steeper than during previous stage and scoured in the upper part. In the bottomset, significant erosion recording sediment bypass downstream toward the pro-delta can be observed. During lowstand normal regression, a starved fine silt to shale bottomset onlaps onto the major erosional surface. The bulk of the coarse-grained sediments is stored in the delta topset and foreset. During the transgressive to highstand stage, the former topset and foreset are eroded by high-density turbidity currents and massive-sandy turbidites are deposited in the bottomset, which onlap onto the foreset beds and form a slope apron geometry in the delta toe.The stratigraphic model improves the prediction for the sand distribution within the various parts of the bottomset. This approach is particularly relevant for clastic depositional systems with high sediment discharge and a high accommodation rate.

La faille d’Aigion appartient à un système de failles normales à pendage nord affectant la bordure sud du golfe de Corinthe, témoin d’une extension active d’échelle régionale caractérisant la région égéenne. Les carottes du forage AIG-10, qui a traversé cette faille, montrent la présence d’une zone endommagée et d’une gouge. Ce travail présente une analyse des lames minces faites à partir de ces carottes. Il confirme la zonation en termes de fracturation à l’approche de la faille. Loin de cette dernière, la fracturation héritée de la phase compressive de l’orogenèse hellénique est dominante, bien qu’il existe aussi une famille E-W liée à l’extension actuelle. Toutes ces fractures sont scellées et le remplissage est similaire d’un point de vue luminescence au calcaire hôte. A l’approche du coeur, la quantité de fractures liées à la faille augmente; le remplissage de ces fractures indique, en cathodoluminescence, le passage de plusieurs fluides qui seraient d’origine externe, et la dernière génération de fractures est encore ouverte. Au mur de la faille, sous 5 m d’épaisseur verticale de cataclasite et d’ultracataclasite dans les calcaires et radiolarites (coeur de faille) et 13 m d’épaisseur verticale de gouge dans les radiolarites, les observations sont plus limitées, car la présence d’un karst a restreint les possibilités de carottage. Néanmoins, on peut observer que le remplissage des fractures liées à l’extension est différent de ce qui nous a été dévoilé au toit. Ceci suggère que la faille, transversalement imperméable aujourd’hui, l’a toujours été. L’analyse de la succession des ciments met en évidence une perméabilité parallèle à la faille à la faveur d’un système de fractures et fentes jeunes et ouvertes, pendant qu’est discuté le transfert de fluides par rapport aux stades de propagation de la faille.

International audience

International audience; Due to the multiple controlling factors involved, it is a challenging task to identify and quantify theprocesses influencing the distribution and heterogeneity of marine organic-rich rocks. To improveour understanding of these deposits, we model their burial history and stratigraphic evolution as wellas processes linked to marine organic matter history throughout the Lower Jurassic in of the NorthernLusitanian Basin (Western Iberian Margin). This 15-Ma-long interval is modelled using 100-kyrtime steps to simulate lithologies and organic matter heterogeneity as layers with a thickness of 2–5 m, depending on the sedimentation rate in the basin. The model is calibrated by well and outcropdata which provide structural and biostratigraphic constraints, as well as information on the depositionalfacies and geochemistry of the sediments. The results show that the presence of organic-richintervals is linked to first-order variations in the basin geometry and sedimentation rates. Withoutconsidering any variation of primary productivity or oxygen content in surface sea waters, theparameters of basin geometry and sedimentation rate are sufficient to predict the main characteristicsof source rocks, i.e. their occurrence, thickness and mineralogy at the basin scale. However, to fit themeasured organic carbon contents, we need to take account of other parameters such as variations ofprimary productivity or changes in dissolved oxygen concentration.

Summary Hydraulic behaviour is controlled, in fault zones, by fracture and pore network properties but the interactions between parameters of the pore, fracture and fault networks and fluid-flow are not fully understood, due to the strong dependence to rock characteristics and external conditions (stress and pressure field, physical and chemical conditions of fluid-flow). To determine the control of these factors on fractured sandstone hydraulic behaviour, an outcrop was selected on the Upper Rhine Graben western border, in the footwall of a normal fault affecting Triassic sandstones. On samples belonging to the damage zone of this fault, pore and petrophysical properties were determined using mercury intrusion porosimetry (MIP), NMR relaxometry and petrography (SEM, cathodoluminescence). The matrix pore network dimensions vary depending on the distance between the sample and the closest fracture plan, and the behavior is different for the two facies identified. These variations are linked with differing mechanisms of deformation and diagenesis for each facies, but both result in an enhanced drainage in the “damage” zone around the fracture. At the fault scale, the hydraulic behaviour can be determined by combining the global fracture intensity and the effect of each single fracture damage zone.

International audience; Gravity-driven processes produce turbiditic systems with an overall downslope direction. Slope, nature of the sea floor and bottom-currents are key parameters constraining the sediment transfer from the delta to the deep-sea fan. They are extensively described in the literature mainly from seismic and in less proportion from outcrop and modern data. Involved internal processes are also intensively studied by numerical modeling. To bridge the gap between the marginal coarse-grained delta and the basin axis depocenter in highsediment supply, we propose to study outcrops of the Ilias Gilbert-type pro-delta along the southern margin of the gulf of Corinth in Greece. An entire sedimentological profile is documented from source-to-Sink based on standard field observations enhanced by 3D photogrammetric models (UAV acquisition), and with a focus on the facies distributions, the facies associations, the internal architectures and the morphologies. The Gilbert-type delta bottomset reveals four bottomset-dynamics under specific processes integrated within a stratigraphic frame. During highstand normal regression, the gravelly bottomset mainly develops under subcritical flow. The supercritical flow undergoes a stationary hydraulic jump in the toeset due to the slope break and becomes subcritical. As a result, a " low-relief channel-levees " system is formed in the bottomset. The channels are reworked by backstepping conglomeratic lenses interbedded with silty concave-up and concave-down levees. During normal regression, the foreset beds are steeper and scoured in the upper part. In the bottomset, significant erosion recording sediment bypass downstream toward the prodelta. During lowstand normal regression, starved fine silt to shale bottomset onlaps onto the major erosional surface. During the transgressive stage, the topset and foreset are eroded by high-density turbidity currents and massive coarse-grained sandy turbidites are deposited in the bottomset, which onlap onto the foreset beds and form a slope apron geometry in the delta toe. Downstream of the Gilbert-type delta bottomsets, the sedimentary system is dominated by conglomeratic channels with an axis of 60° from the delta axis (fault controlled. The channels are limited by both external and internal levee with specific facies and architecture. They are commonly characterized by low sinuosity geometries. The external levee could locally include sediment waves. This study provides the key elements to recognize the specific facies and architectures of the different bottomset typologies in relation with the associated turbiditic system. These sedimentary and stratigraphic models improve the prediction for the sand and conglomerate distribution and their connectivity within the various parts of the delta toe in a clastic depositional profile induces by a high-sediment discharge.

This study presents the results of two field tests that aimed at evaluating two countermeasures (WESP and GGH) to avoid acid mist formation. A WESP is shown to be very efficient for the removal of nuclei from the flue gas (100 % efficient) and thus can prevent aerosol formation inside an amine based absorber. This is however only valid in the absence of SO2 in the flue gas entering the WESP. A decreasing WESP efficiency is noted in the presence of SO2 with increasing voltages as a result of newly formed aerosols inside the WESP. This implies that no or very low levels of SO2 should be present in the flue gas entering the WESP. Since most of the amine carbon capture installations have a pre-scrubber (usually using NaOH to remove residual SO2 in the flue gas leaving the power plant's Flue Gas Desulphurisation) in front of their amine absorber, the WESP must be installed behind this pre-scrubber and not in front of it. Having a Gas-Gas Heater (or any type of flue gas cooling such as a Low Temperature Heat Exchanger) installed upstream of the wet scrubbing may prevent homogenous nucleation and thus prevent the conversion of H2SO4 into sulfuric acid aerosols and consequently mist formation issues in the amine based carbon capture installation. Which option to choose amongst the two countermeasures presented in this study will depend on whether a new built installation is being considered or whether a carbon capture is planned as a retrofit into an existing installation. (C) 2017 The Authors. Published by Elsevier Ltd.

Shale reservoirs have not benefited from advanced modeling tools to the extent of conventional resources. Thus an approach is proposed to integrate key parameters, such as total organic carbon (TOC) content, methane adsorption and organic porosity in a basin simulator. Original TOC has an impact on both gas generated volume and gas retention within source rocks. The conversion of organic matter into hydrocarbons also creates additional intraparticle kerogen porosity in which oil and gas can be stored. In this work, a method is proposed to calculate the evolution of TOC, organic porosity and gas retention capacity (free versus adsorbed) through time in shale gas by means of petroleum system modeling. Gas adsorption potential on organic material is calculated using a Langmuir model, which accounts for pressure, temperature and remaining solid TOC. Organic porosity is calculated as the result of the change of the organic matter from solid immature kerogen to less dense fluid hydrocarbons during thermal maturation. The method is tested on a 3D basin model of the Mississippian Barnett Shale in Texas (USA). The computed organic porosity varies from 0% in immature zones, to a maximum of 4% of rock volume in organic-rich and mature zones. Computed retained methane in the Lower Barnett Shale ranges between 20 and 60 scf/t (from 1 to nearly 3 kg/m3) and is mainly concentrated in mature areas of the basin. Simulated results are consistent with available Barnett Shale data. Possible effects of assumptions made in the approach and perspectives are discussed.

The overall rifting history of the Corinth basin in Greece is still debated due to (1) the lack of deep wells to constrain the offshore domain, (2) sparse dating available onshore and (3) the only few integrated basin-scale studies covering both offshore and onshore data providing an homogeneous overview of its stratigraphic architecture. This paper provides an update to the structural and stratigraphic architecture of the Corinth rift through the results of field mapping, geological and structural map synthesis, outcrop stratigraphic characterization and seismic sequence stratigraphic correlations. A comparison with the surrounding basins to extrapolate ages and a correlation between onshore stratigraphic architecture and offshore seismic stratigraphy in the Corinth rift are proposed to establish time lines of the key stages during the rift evolution, and its relationship with the previous Hellenic compressive phase and the Aegean back-arc opening eastward. The rift history can be subdivided into two major syn-rift phases. A Syn-rift 1 including (a) the rift initiation at around 5.3 Ma with continental to lacustrine sediments deposited in km-scale isolated depocenters. (b) The rift widening (ca. 5.3–3.0 Ma) combined with a rift propagation from east to west. First marine incursions were recorded along the Corinth Isthmus. At that time, the rift was still subdivided into numerous 2–10 km-wide depocenters controlled by active faults where continental to lacustrine deposits occurred. The depocenters progressively grew and became linked. (c) The Syn-rift 1 “climax” (ca. 3.0–2.6 Ma) with 15–25 km-long fault segments subdivided the rift into 5–10 km wide fault blocks. Sedimentation was characterized by thick alluvial fans and large Gilbert-type deltas along the active fault segments and a starved basin along the basin axis. Marine connection with the Mediterranean Sea was dominantly established thought the Corinth Isthmus. (d) The Syn-rift 1 phase ended with a basinward fault migration phase (ca. 2.6–0.8 Ma) characterized by a progressive demise of the rift border fault and a rapid forced regressive trend recorded by the large Gilbert-type deltas. Bathymetry continued to increase along the basin axis. An additional phase of rifting (Syn-rift 2) ensued, and was characterized by the Peloponnesus margin uplift combined with an increase of both tectonic and total subsidences in the basin axis (ca. 0.8 Ma to present day). The depositional profile was shorter than during the previous stages, the rift progressively narrowed and the sedimentation rate strongly increased in the depocenter. The short lived duration of each phase and the peculiarity of the present phase are discussed in relation to the inherited structures and relative influence of the far field stress changes within the global context of the Hellenic subduction.

We propose a basin-scale (∼300 × 100 km) study of the pre-salt to salt sedimentary fill from the Suez rift based on outcrop and subsurface data. This study is a new synthesis of existing and newly acquired data using an integrated approach with (1) basin-scale synthesis of the structural framework, (2) stratigraphic architecture characterization of the entire Suez rift using sequence stratigraphy concepts, (3) lithologic maps reconstruction and interpretation, (4) isopach/depocenter maps interpolation to quantify sedimentary volumes, and (5) quantification of the sediment supply, mean carbonate and evaporite accumulation rates, and their integration into the rift dynamic. The Gulf of Suez is ca. 300-km-long and up to 80-km-wide rift structure, resulting from the late Oligocene to early Miocene rifting of the African and Arabian plates. The stratigraphic architecture has recorded five main stages of rift evolution, from rift initiation to finally tectonic quiescence characterized by salt deposits. Rift initiation (ca. 1–4 Myr duration): the Suez rift was initiated at the end of the Oligocene along the NNW-SSE trend of the Red Sea with evidences of active volcanism. Continental to lacustrine deposits only occurred in isolated depocenters. Sediment supply was relatively low. Rift widening (ca. 3 Myr duration): the rift propagated from south to north (Aquitanian), with first marine incursions from the Mediterranean Sea. The rift was subdivided into numerous depocenters controlled by active faults. Sedimentation was characterized by small carbonate platforms and associated sabkha deposits to the south and shallow open marine condition to the north with mixed sedimentation organized into an overall transgressive trend. Rift climax (ca. 5 Myr duration): the rift was then flooded during Burdigalian times recording the connection between the Mediterranean Sea and the Red Sea. The faults were gradually connected and reliefs on the rift shoulders were high as evidenced by a strong increase of the uplift/subsidence rates and sediment supply. Three main depocenters were then individualized across the rift and correspond to the Darag, Central, and Southern basins. Sedimentation was characterized by very large Gilbert-type deltas along the eastern margin and associated submarine fans and turbidite systems along the basin axis. Isolated carbonate platforms and reefs mainly occurred in the Southern basin and along tilted block crests. Late syn-rift to rift narrowing (ca. 4 Myr duration): during the Langhian, the basin recorded several falls of relative sea level and bathymetry in the rift axis was progressively reduced. The former reliefs induced during the rift climax were quickly destroyed as evidenced by the drastic drop in sediment supply. Stratigraphic reconstruction indicates that the Central basin was restricted during lowstand period; meanwhile, open marine conditions prevailed to the north and south of the Suez rift. The Central basin, Zaafarana, and Morgan accommodation zones thus acted as a major divide between the Mediterranean Sea and the Red Sea. During Serravalian times, the Suez rift also recorded several disconnections between the Mediterranean and Red seas as evidenced by massive evaporites in major fault-controlled depocenters. The Suez rift was occasionally characterized by N–S paleogeographic gradient with restricted setting to the north and open marine setting to the south (Red Sea). Tectonic quiescence to latest syn-rift (ca. 7 Myr duration): the Tortonian was then characterized by the deposition of very thick salt series (>1000 m) which recorded a period of maximum restriction for the Suez rift. The basin was still subdivided into several sub-basins bounded by major faults. The basin with a N-S paleogeographic gradient was totally and permanently disconnected from the Mediterranean Sea and connected to open marine condition via the Red Sea. The Messinian was also characterized by a thick salt series, but the evaporite typology and sedimentary systems distribution suggest a more humid climate than during Tortonian times. Pre-salt to salt transition was not sharp and lasted for ca. 4 Myr (Langhian-Serravalian). It was initiated as the result of the combined effect of (1) climatic changes with aridization and low water input from the catchments and (2) rift dynamic induced by plate tectonic reorganization that controlled the interplay between sea level and accommodation zones constituting sills.

The Colombian Andean foreland is a rich petroleum province, where various source rocks and an active circulation of fresh water are present in the subsurface, resulting in a complex fluid mixture within the reservoirs. Moreover, some of the traps are shallow, and low °API gravity oils are found. Massive meteoric water infiltration and local biodegradation have been proposed to explain these observations, but require some in-depth investigation to be confirmed. In order to provide some new insights into the Llanos Basin petroleum system, we performed a natural gas geochemical survey over different areas of the basin, including stable isotopes of hydrocarbon, non-hydrocarbon and noble gases. Results show that the influence of meteoric water infiltration is dominant in the shallow area eastward, but decreases towards the deepest part of the basin westward. A general gas/oil phase separation differentiates gas-depleted biodegraded, shallow reservoirs from deep gas-rich less-altered reservoirs. Data suggest that there is a shallow biodegradation associated with meteoric water circulation in the Carbonera Fm, while some of the deeper heavy oils (Mirador, Une fms) were more likely produced by an early mature source rock. However, biodegraded oil later mixed with less altered oil and associated gas are plausible. This study also indicates a contribution of mantle fluids in the deepest parts of the basin near the contact with the Guaycaramo Fault System. There, older rift sequences may have recorded mantle fluid fluxes, or alternately the presence of diffuse mantle fluxing along the deep-rooted thrust front during the formation of the Llanos Basin.