Éditeur(s) : HAL CCSD
Résumé : Geothermal energy is considered as a green and infinite energy source at human scale. Currently, the yield of geothermal power plants is limited to temperatures of the operating fluid which 350 °C. From tectonic and volcanic activity at mid-ocean ridges, Iceland is a location where supercritical fluid extraction (T> 375 °C) can considered for the near future. Exploiting such fluids could theoretically multiply by a factor of ten the electrical power delivered by geothermal wells. Can such fluids circulate at the base of brittle oceanic crust? This work investigates the petrophysical properties of basalts in order to constrain geophysical observations in Iceland and predict the behavior of very high temperature geo-hydrothermal reservoirs. The first approach consisted in studying the physical properties of rocks that have hosted deep hydrothermal circulations at oceanic ridges. The study of these rocks at ODP Site 1256 shows that the porosity measured both in the field and in the lab is associated with amphibolite facies alteration minerals (T> 500 ° C). The second approach was to recreate in the laboratory the conditions of pressure, temperature and pore fluid pressure of high temperature to supercritical hydrothermal systems to predict the mechanical and electrical properties of basalts under these conditions. The mechanical results indicate that the brittle/ductile transition occurs at a temperature of about 550° C, where a strong permeability decrease is expected. The implementation and calibration of a new cell for measuring electrical conductivity at high temperature provide the first results for the interpretation of geophysical data. When applied to basaltic crustal conditions in Iceland, these results indicate that hydrothermal fluids could circulate, at least temporarily, in a supercritical state up to 5 km depth.
La géothermie est considérée comme une source d'énergie propre et inépuisable à échelle humaine. Actuellement, le rendement des centrales géothermiques est limité à l'exploitation de fluides de températures inférieures à 350 °C. L'association de l'activité tectonique et volcanique aux dorsales océaniques fait de l'Islande un lieu où l'extraction de fluides supercritiques (T> 375 °C) peut être envisagée. Cette exploitation pourrait multiplier par dix la puissance électrique délivrée par le système géothermal. Ces fluides peuvent-ils circuler dans la croûte océanique ? Ce travail propose de contraindre les observations géophysiques et de prédire le fonctionnement des réservoirs géo-hydrothermaux de très haute température par l'étude des propriétés physiques des basaltes. La première approche est focalisée sur l'étude de roches ayant accueilli une circulation hydrothermale par le passé. L'étude de ces roches au site ODP 1256, montre que leur porosité est associée à la présence de minéraux d'altération hydrothermale du facies amphibolite (T> 500 °C). La seconde approche a consisté à recréer, en laboratoire, les conditions des systèmes hydrothermaux, à très haute température, afin de prédire les propriétés mécaniques et électriques des basaltes dans ces conditions. Les résultats mécaniques indiquent que la transition fragile/ductile, souvent associée à une forte décroissance de perméabilité, intervient à une température d'environ 550 °C. La mise en place d'une cellule de mesure de la conductivité électrique de haute température a fourni les premiers résultats utiles à l'analyse des données géophysiques. Appliqués aux conditions de la croûte basaltique Islandaise, ces résultats indiquent que des fluides hydrothermaux pourraient circuler au moins transitoirement à l'état supercritique jusqu'à ~ 5 km de profondeur.
https://tel.archives-ouvertes.fr/tel-00591798

tel-00591798
https://tel.archives-ouvertes.fr/tel-00591798
https://tel.archives-ouvertes.fr/tel-00591798/document
https://tel.archives-ouvertes.fr/tel-00591798/file/THESE_MV_pro.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
During the early years of the Iceland Deep Drilling Project (IDDP), development of three distinctive technological and scientific approaches were formalised and then carried out until 2010 within a European funded project called HiTI (high temperature instruments for supercritical geothermal reservoir characterisation and exploitation). These approaches were: (1) development of several downhole instruments allowing them to function up to 300 ◦C and 400 ◦C, (2) identification of two new Na/Li cation ratio geothermometric relationships valid at very high temperature, (3) tracer testing with high temperature tolerant organic isomers and finally and (4) basalt rock deformation and petrophysical properties laboratory investigations at high temperature and pressure conditions.
ISSN: 0375-6505

hal-00921127
https://hal-brgm.archives-ouvertes.fr/hal-00921127
DOI : 10.1016/j.geothermics.2013.07.008

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The mechanism for tree orientation in angiosperms is based on the production of high tensile stress on the upper side of the inclined axis. In many species, the stress level is strongly related to the presence of a peculiar layer, called G-layer, in the fibre wall. The structure of G-layer has been recently described as a hydrogel thanks to N2 adsorption-desorption isotherms of supercritically dried samples showing a high mesoporosity (pores size from 2 to 50 nm). This led us to revisit the concept of G-layer that was until now only described from anatomical observation. Adsorption isotherms of both normal wood and tension wood have been measured on six tropical species. Measurements show that mesoporosity is high in tension wood with typical thick G-layer while it is much less with thinner G-layer, sometimes no more than normal wood. The mesoporosity of tension wood species without G-layer is as low as in normal wood. Not depending on the amount of pores, the pore sizes distribution are always centred around 6-12 nm. These results suggest that, among species producing fibres with G-layer, large structural differences of G-layer exist between species
ISSN: 0022-0957

hal-00387861
https://hal.archives-ouvertes.fr/hal-00387861
DOI : 10.1093/jxp/erp133

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Fromthe Proterozoic to the Quaternary, the evolution of the Earthwas characterised by recurrent periods of glaciation.However, the margins of many ancient ice-sheets are poorly defined on palaeogeographic reconstructions.The extent and outlines of ancient ice sheets can be better understood through careful documentation ofsediments deposited at the ice-sheet margin. An outstanding example is provided herein based on an end-Ordovician archive in Libya (Tihemboka area, Murzuq Basin). The four sets of structures include: i) subglacialglaciotectonic structures and soft sediment deformations from flowing glacier ice, such as intraformational glacialstriae, intraformational deformation (shear planes, sheath folds), normal microfaults, and large-scaleglaciotectonic folds-and-thrusts; (ii) structures resulting from overpressured subglacial (meltwater) flowssuch as clastic dykes and tunnel valleys; (iii) proglacial depositional structures and facies related to highmagnitudemeltwater floods such as sandstone intraclasts, large-scale bedforms resulting from supercriticalflows, climbing-dune cross-stratification and kettle holes; and (iv) deformation structures resulting from freefloating and nonglacier ice such as ice-keel scours and ice-crystal marks. Such a set of structures points to anice-marginal (essentially continental) depositional setting, and provides an excellent suite of criteria to identifymargins of ancient ice sheets in the stratigraphic record. At a regional scale, a reconstruction through time andspace of the related depositional wedge is proposed. This corresponded to a seismic-scale (N120 m in thickness,40 km in length) ice-marginal wedge in front of an essentially warm-based ice-sheet inducing concomitantlarge-scale glaciotectonic deformation, glacial basin and tunnel valley downcuttings. The related ice-front wasassociated with high-energy meltwater flows feeding a network of deeply incised proglacial channels downstreamand, beyond them, a fluvioglacial deltaic system. Shallow ice-marginal permafrost most likely affectedthe depositional wedge. At a larger scale, the Tihemboka ice-marginal wedge is interpreted as related to a stillstandperiod over the Gondwana platform, developed over an estimated interval of a few thousands of years.Based on these data, the conditions that arose in a particularly favourable context for the development, the preservationand the identification of ice-marginal wedges in the geological record are reviewed. Significantmeltwater-derived sediment deposition and aggradation in an accommodation space resulting either frompreglacial inheritance, glacial downcuttings and/or glacio-isostatic lithospheric flexure, or active tectonic subsidence(>1 Myr) are required for their formation and subsequent preservation.
ISSN: 0012-8252

insu-01184739
https://hal-insu.archives-ouvertes.fr/insu-01184739
DOI : 10.1016/j.earscirev.2015.06.006

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Despite a relatively 'uniform' fertile composition (Al2O3 = 2 center dot 19-4 center dot 47 wt %; Fo% = 89 center dot 2 +/- 0 center dot 3%; Cr#(Spl) = 8 center dot 9 +/- 1 center dot 5%), the Montferrier peridotite xenoliths show a wide range of S contents (22-590 ppm). Most sulphides are interstitial and show peculiar pyrrhotite-pentlandite intergrowths and low abundances of Cu-rich phases. Sulphide-rich samples are characterized by strong enrichment in the light rare earth elements and large ion lithophile elements without concomitant enrichment of the high field strength elements. Such trace-element fractionation is commonly ascribed to metasomatism by volatile-rich melts and/or carbonatitic melts. S and Se (11-67 ppb), as well as S/Se (up to approximate to 12 000), are correlated with La/Sm. Cu, however, remains broadly constant (30 +/- 5 ppm). These features strongly suggest that the percolation-reaction of such volatile-rich fluids has led to sulphide enrichment with an atypical signature marked by strong fractionation of the chalcophile elements (i.e. S vs Se and Cu). S-rich xenoliths are also characterized by high (Pd/Ir)(N) (1 center dot 2-1 center dot 9; where subscript N indicates normalized to chondrite), (Pd/Pt)(N) between 1 center dot 5 and 2 center dot 2, and (Os/Ir)(N) up to 1 center dot 85. Despite the relative uniform fertile composition of the xenoliths, Re/Os ranges between 0 center dot 02 and 0 center dot 18. Os-187/Os-188 is extremely variable even within a single sample and can be as high as 0 center dot 1756 for the most S-rich samples. Sulphides show highly fractionated and variable abundances of the highly siderophile elements (HSE) [0 center dot 03 (Pd/Ir)(N) < 1283] and Re-Os isotopic composition (0 center dot 115 < Os-187/Os-188 < 0 center dot 172). Such variation can be observed at the thin-section scale. Whole-rock and in situ sulphide data demonstrate that chalcophile and HSE systematics and the Os isotopic composition of the upper mantle could be significantly modified through metasomatism, even with volatile-rich fluids. These features highlight the complex behaviour of the HSE in fluid-rock percolation-reaction models and suggest a complex interplay between sulphide addition (crystallization or sulphidation) and partial equilibration of pre-existing sulphide. The specific fractionations observed in chemical proxies such as S and Se, Os and Ir, and Pd and Pt, as well as the low abundance of Cu-rich sulphides, suggest that sulphide addition may not have occurred via sulphide melts. Rather, we infer that S was present as a dissolved species in a (supercritical) oxidizing, volatile-rich fluid (C-O-H-S +/- Cl) along with other chalcophile and siderophile elements such as Os, Pd, Re and Au. The highly radiogenic Os composition of this fluid ( Os-187/ Os-188 > 0 center dot 17) would imply that such fluids are derived from an uncommon type of mantle source possibly related to carbonatite melts.
ISSN: 0022-3530

hal-00644524
https://hal.archives-ouvertes.fr/hal-00644524
DOI : 10.1093/petrology/egr038

Éditeur(s) : HAL CCSD Oxford University Press (OUP): Policy B - Oxford Open Option A
Résumé :  
The mechanism for tree orientation in angiosperms is based on the production of high tensile stress on the upper side of the inclined axis. In many species, the stress level is strongly related to the presence of a peculiar layer, called the G-layer, in the fibre cell wall. The structure of the G-layer has recently been described as a hydrogel thanks to N2 adsorption-desorption isotherms of supercritically dried samples showing a high mesoporosity (pores size from 2-50 nm). This led us to revisit the concept of the G-layer that had been, until now, only described from anatomical observation. Adsorption isotherms of both normal wood and tension wood have been measured on six tropical species. Measurements show that mesoporosity is high in tension wood with a typical thick G-layer while it is much less with a thinner G-layer, sometimes no more than normal wood. The mesoporosity of tension wood species without a G-layer is as low as in normal wood. Not depending on the amount of pores, the pore size distribution is always centred around 6-12 nm. These results suggest that, among species producing fibres with a G-layer, large structural differences of the G-layer exist between species.
Journal of Experimental Botany

hal-01032161
https://hal.archives-ouvertes.fr/hal-01032161
DOI : 10.1093/jxb/erp133

Éditeur(s) : HAL CCSD
Résumé : International audience
The carbon capture and storage is considered as one of the solutions of reducing the effects of global warming. It consists in injecting large quantities of CO 2 in supercritical form directly into deeply located geological formations. One of the methods involves sequestration in the carbonate sedimentary rocks (sandstones and limestones) which are considered as a promising solution. The morphology of the pore network and solid skeleton defines important macroscopic prop-erties of the rock (permeability, stiffness). Modelling at micro scale of random heterogeneous materials (porous media) should be based on morphological and statistical characterisation 1,2 of the investigated microstructure. The work is focused on a reconstruction method by grains deposit 3 , for various range of pa-rameters, to obtain equivalent model of natural rock samples (oolitic limestone and fontainebleau sandstone). Generated samples satisfy morphological and statistical informations 4 which were obtained by 3D image analysis of X-ray tomography of the natural rock samples. For validation of the modelling numerical computations of mechanical and transfer properties are also provided.
14th European Mechanics of Materials Conference - EMMC14
Gothembourg, Sweden

hal-01103163
https://hal.archives-ouvertes.fr/hal-01103163

Éditeur(s) : HAL CCSD
Résumé : International audience
The purpose of our study is to model a geothermal reservoir. When geothermal reservoir are assumed to be composed of pure water, the transfer of mass and energy is classically described by two balance equations: mass balance equation and the energy balance equation. In addition to those equations, fluid velocity ist classically given by the Darcy law while thermodynamic properties, inferred from theoretical or empirical equations of state, are used to close the mathematical system. Once this system is closed, there exist different solutions. The first one is to solve for pressure and temperature with a variable switch to saturation in the two-phase region (e.g. TOUGH2). The second one is to solve for pressure and enthalpy to increase stability of phase transition between single and two-phase states (e.g. Hydrotherm). We adopted the second option and chose te use a splitting method to get rid of the complexity of coupling equations and a finite volume method for the spatial discretization. Selecting object-oriented languages, we developed a multi-language framework, combining Python, Fortran and a C++ implementation of IAPWS (from the freesteam project) including the supercritical equations, in porous media velocity is given by Darcy law and to close the system physical properties are determined by the IAPWS-IF97 thermodynamic formulation. We resolve the equations in pressure and enthalpy instead of pressure and temperature in order to increase stability and to handle easier the passage from a single-phase to a two-phase system. We solve the system by using a splitting method - to get rid of the complexity of coupling equations - and a finite volume method. We offer some freedom to users thanks to the implementation of several methods like explicit or implicit Euler, Runge-Kutta or BDF2 for time solvers or GMRES and BICGSTAB for the linear solver. We can handle several boundary conditions like no-flow - describing a boundary which can not exchange matter with the exterior - or like a mixed-therm condition - a Dirichlet condition to the pressure and a Dirichlet or an outflow condition to the temperature in order to describe a recharge or a discharge zone - ... We're developing a multi-language framework, combining Python, Fortran and the C++ implementation of IAPWS (from the freesteam project). All these languages are object-oriented. We've applied this simulation model to the dogger in Paris, France, to several one-dimensional systems and a two-dimensional one made by Coumou with the CSMP++ platform. The dogger is a reservoir exploited to produce heat by pumping water at 70 and reinjecting it in the reservoir at 40. In the one-dimensional systems we wanted to observe the process of heat transfer from a higher temperature boundary to a smaller one in a high-energy domain. The last simulation shows the natural convection of water in a fault. For every simulation we compared the solutions we found with an other code (TOUGH2 or CSMP++) and they agreed. The next step will be to model the geothermal plant in Guadeloupe, West Indies. It's the only place in France - and in the West Indies so far - producing electricity with the earth power. The temperature can reach up to 1000 and the pressure range is around a few hundreds MPa. In some surface zones we can see two-phase water at atmospheric pressure. In the 1980s Bouillante was a laboratory for France. Since 1995 Bouillante has given 30GWh electricity a year to the Guadeloupeans.
PROCEEDINGS, Thirty-Ninth Workshop on Geothermal Reservoir Engineering
Stanford, United States

Droits : info:eu-repo/semantics/OpenAccess
hal-00944133
https://hal-brgm.archives-ouvertes.fr/hal-00944133
https://hal-brgm.archives-ouvertes.fr/hal-00944133/document
https://hal-brgm.archives-ouvertes.fr/hal-00944133/file/Copol.pdf