Multi-scale distribution of fractures in crystalline basement,Influence of structural inheritance. Examples of the proximal oblique margins of the Gulf of Aden and Catalonia

La découverte de nombreux réservoirs fracturés dans le socle a considérablement relancé l'intérêt porté sur l'étude de la fracturation du socle. Une meilleure compréhension des relations d'échelles qui caractérisent la géométrie des systèmes fracturés estDevelopment of basement fractured reservoirs in and around igneous rocks have been carried out in recent years. Analyses of field rock analogues are thus required for a better understanding of the scaling characteristics of fracture systems, which coul

Distribution multi-échelle de la fracturation dans les réservoirs cristallins (Influence de l'héritage structural. Exemples des marges obliques proximales du golfe d'Aden et de Catalogne)

La découverte de nombreux réservoirs fracturés dans le socle a considérablement relancé l intérêt porté sur l étude de la fracturation du socle. Une meilleure compréhension des relations d échelles qui caractérisent la géométrie des systèmes fracturés est donc nécessaire, dans le but de guider l interprétation des données régionales et de les extrapoler à d autres échelles. Une cartographie multi-échelle des systèmes fracturés des socles cristallins du Yémen et de Catalogne a été décrite à travers des analyses statistiques des différents paramètres géométriques. Le réservoir fracturé analogue est défini suivant un modèle à double porosité dans lequel les systèmes tectoniques et les systèmes de joints correspondent respectivement à la colonne vertébrale et à la matrice du réservoir. Ces deux entités montrent des propriétés géométriques, réservoir et d échelle contrastées. Dans les systèmes tectoniques, les géométries multi-échelles sont auto-similaires, montrent des comportements fractals et les zones de failles présentent une organisation hiérarchique. Dans les systèmes de joints, le réseau de fractures est dépendant de l échelle et les espacements sont réguliers ou aléatoires. De plus, le rôle de l héritage structural a été investigué. Les principaux résultats montrent que (i) la dimension et l orientation des structures héritées sont des paramètres majeurs qui contrôlent la compétition entre réactivation et néoformation et (ii) le découplage structural entre deux niveaux crustaux possédant un héritage structural hétérogène (e.g. le socle et sa couverture sédimentaire) est contrasté et peut être efficace sans niveau de décollement.Development of basement fractured reservoirs in and around igneous rocks have been carried out in recent years. Analyses of field rock analogues are thus required for a better understanding of the scaling characteristics of fracture systems, which could guide both the interpretation of regional data, and its extrapolation to other different scales. Multi-scale mappings of extensional fracture systems in the crystalline basements of Yemen (panafrican) and Catalonia (hercynian) are described through statistical analyses of several geometrical parameters. The fractured reservoir analogue is defined with a dual porosity model in which tectonic and joint systems correspond to the basement reservoir backbone and matrix respectively. These two end-members reveal contrasting geometrical, reservoir, and scaling properties. In tectonic systems, multi-scale geometries are self-similar , the fracture network shows fractal behavior, and fault zones show hierarchical organization of geometrical parameters such as length, thickness, and spacing. In joint systems, the fracture network is scale dependent with negative exponential length distribution, and shows anti-clustered spacing. In addition, the role of structural inheritance in basement fracture systems has been investigated. Main results show that (i) size and orientation of inherited structures are major parameters which controlled competition between reactivation and neoformation and (ii) structural decoupling between layered crustal levels having heterogeneous structural inheritance (e.g. basement versus sedimentary cover) is contrasting and could be effective without an intermediate decollement level.STRASBOURG-Géologie (674822251) / SudocSudocFranceF

P/T ratio in high-pressure rocks as a function of dip and velocity of continental subduction

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Geometry and kinematics of continental subduction inferred from 1D thermal modelling of prograde PT path

International audienc

Evolution of the NW Zagros Fold-and-Thrust Belt in Kurdistan Region of Iraq from balanced and restored crustal-scale sections and forward modeling

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Physical properties of fault zones within a granite body: Example of the Soultz-sous-Forêts geothermal site

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TMS and neuronavigation in treatment of depression: a view into the future

National audienc

A multiscale analysis of a fracture pattern in granite: A case study of the Tamariu granite, Catalunya, Spain

International audienceThe in-depth investigation of fractured reservoirs is mainly limited to geophysical data that is in 3D and mostly on the scale of hundred meters to several kilometers or boreholes data that is in 1D and at meter to lower scale. The study of outcropping analogues of buried reservoirs is therefore a key tool for the characterization of the fault and fracture network at the reservoir scale. Tamariu granite has been the subject of this study with the aim to analyse faults and fractures from seismic to borehole scale. With the combination of satellite picture at different resolution and field study, we perform a statistical analysis focused of the length and orientation from infra centimeter crack to hundred kilometer length fault. On the whole range of scale studied, i.e. on 7 orders of magnitude, we have defined a length distribution following a power-law with an exponent a ¼ À2. On the contrary to the length that can be modelled with a unique law, the orientation data shows a variation depending on the scale of observation: as the fault and fracture sets are suitable from the regional faults to the centimeter crack, the proportion of the sets varies at each scale of observation

Structural control of weathering processes within exhumed granitoids: Compartmentalisation of geophysical properties by faults and fractures

In the latter stages of exhumation processes, rocks undergo weathering. Weathering halos have been described in the vicinity of structures such as faults, veins or dykes, with a lateral size gradually narrowing with depth, symmetrically around the structures.In this paper, we describe the geophysical characterisation of such alteration patterns on two granitoid outcrops of the Catalan Coastal Ranges (Spain), each of which is affected by one major fault, as well as minor faults and fractures. Seismic, electric and ground penetrating radar surveys were carried out to map the spatial distribution of P-wave velocity, electrical resistivity and to identify reflectors of electromagnetic waves. The analysis of this multi-method and complementary dataset revealed that, at shallow depth, geophysical properties of the materials are compartmentalised and asymmetric with respect to major and subsidiary faults affecting the rock mass. This compartmentalisation and asymmetry both tend to attenuate with depth, whereas the effect of weathering is more symmetric with respect to the major structure of the outcrops. We interpret such compartmentalisation as resulting from the role of hydraulic and mechanical boundaries played by subsidiary faults, which tend to govern both the chemical and physical alterations involved in weathering. Thus, the smoothly narrowing halo model is not always accurate, as weathering halos can be strongly asymmetrical and present highly irregular contours delimiting sharp contrasts of geophysical properties.These results should be considered when investigating and modelling fluid storage and transfer in top crystalline rock settings for groundwater applications, hydrocarbon or geothermal reservoirs, as well as mineral depositsWe are grateful to ADEME (France) and EIfER (Germany) for funding this study. We would also like to thank Julien Guillemoteau (Université de Strasbourg) and Hagen Dekert (IGEM) for their help in carrying out the “espectacular” field work that provided the datasets used in this study.Peer reviewe

Scaling and geometric properties of extensional fracture systems in the proterozoic basement of Yemen. Tectonic interpretation and fluid flow implications

International audienc