Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Diffusion parameters for HTO, 36Cl−, and 125I− were determined on Upper Toarcian argillite samples from the Tournemire Underground Research Laboratory (Aveyron, France) using the through diffusion technique. The direction of diffusion was parallel to the bedding plane. The purpose of the present study was 3-fold; it was intended (i) to confirm the I− interaction with Upper Toarcian argillite and to verify the effects of initial I− concentration on this affinity, as previously observed by means of radial diffusion experiments, (ii) to highlight any discrepancy between Cl− and I− diffusivity, and (iii) to investigate the effect of an increase of the ionic strength of the solution on the anionic tracers' diffusive behaviour. The results show that the effective diffusion coefficient (De) and diffusion accessible porosity (εa) values obtained with an ionic strength (I.S.) synthetic pore water of 0.01 eq L−1 are: De = 2.35-2.50 × 10−11 m2 s−1 and εa = 12.0-15.0% for HTO, and De = 14.5-15.5 × 10−13 m2 s−1 and εa = 2.5-2.9% for 36Cl−. Because of anionic exclusion effects, anions diffuse slower and exhibit smaller diffusion accessible porosities than HTO, taken as a water tracer. The associated effective diffusion coefficient (De) and rock capacity factor (α) obtained for 125I are: De = 7.00-8.60 × 10−13 m2 s−1 and α = 4.3-7.2%. Such values make it possible to calculate low 125I distribution ratios (0.0057 < RD < 0.0192 mL g−1) which confirm the trend indicating that the 125I rock capacity factor increases with the decrease of the initial I− concentration. Additional through-diffusion experiments were carried out with a higher ionic strength synthetic pore water (I.S. = 0.11 eq L−1). No evolution of HTO diffusion parameters was observed. The anionic tracers' effective diffusion coefficient increased by a factor of two but no clear evolution of their accessible porosity was observed. Such a paradox could be related to the particularly small mean pore size of the Upper Toarcian argillite of Tournemire. The most significant finding of this study is the large discrepancy (factor of two) between the values of the effective diffusion coefficient for 125I and 36Cl. Whatever the ionic strength of the synthetic solution used, 125I exhibited De values two times lower than those of 36Cl. A detailed explanation for this difference cannot be given at present even if a hypothesis based on ion-pairing or on steric-exclusion cannot be excluded. This makes questionable the assumption usually made for quantifying 125I sorption and postulating that 36Cl and 125I would diffuse in the same porosity. In other terms, at Tournemire, 125I sorption could be more pronounced than previously indicated.
ISSN: 0883-2927

hal-00757749
https://hal.archives-ouvertes.fr/hal-00757749
DOI : 10.1016/j.apgeochem.2011.12.017

Éditeur(s) : HAL CCSD
Résumé : The coastal intrusion of brine threatens populations. This is particularly prejudicial in carbonate environments. We have studied the Miocene coral reef of S-E Majorca for better understanding the relation between geological structure and intrusion. For that purpose, we have used multi-scalar and multi-disciplinary methods. The measurements in 25 boreholes over the whole coral platform have allowed defining the stratigraphic structure and some elements of the regional tectonic. The reef progrades in the NE-SW direction, starting from the Aquitanian to terminates at the Messinian. The Messinian Salinity Crisis involves a disappearance of the Mediterranean corals and results in a Terminal Carbonate Complex which overlays a great part of the previously living corals of Majorca. At the experimental site scale, the study of the mineral composition, the texture, and the diagenesis have allowed characterization of the carbonate sequence heterogeneity. Layers of mineralization accompanied by dolomitization and low porosity correspond to postdepositional eustatic levels. The causes for the existence and the orientation of fractures are studied. The permeability to porosity relation is approached. The porosity structure is studied by comparison between primary and secondary porosity. This study contributes to the knowledge of the world best documented site for the evolution of carbonate reef reservoirs, with applications for brine intrusion and for hydrocarbon extraction.
Les intrusions d'eau salée en zone côtière constituent une menace pour la population. Celles-ci sont particulièrement dommageables en contexte carbonaté. Nous avons étudié le récif corallien Miocène du sud-est de Majorque afin de comprendre la relation entre structure géologique et intrusion. Pour cela nous avons utilisé des méthodes multi-scalaires et multi-disciplinaires. Les mesures dans 25 forages sur l'ensemble de la plateforme corallienne ont permis de préciser la structure stratigraphique et certains éléments de la tectonique régionale. Le récif prograde dans la direction NE-SO, en partant de l'Aquitanien pour aboutir au Messinien. La Crise de Salinité Messinienne entraîne une disparition des coraux méditerranéens et se traduit par un Complexe Carbonaté Terminal qui s'étend sur une grande partie des coraux autrefois vivants de Majorque. A l'échelle du site expérimental, l'étude de la composition minérale, de la texture et de la diagenèse ont permis de caractériser l'hétérogénéité de la séquence carbonatée. Des couches de minéralisation accompagnées de dolomitisation et de faible porosité correspondent à différents niveaux eustatiques post-dépositionnels. Les causes de l'existence et de l'orientation des fractures sont étudiées. La relation de perméabilité à porosité est précisée. La structure de porosité est étudiée par comparaison entre la porosité primaire et la porosité secondaire. Cette étude contribue à la connaissance du site le mieux documenté au monde pour l'évolution des réservoirs carbonatés récifaux, avec applications pour les intrusions d'eau salée et l'extraction des hydrocarbures.
https://tel.archives-ouvertes.fr/tel-00440019

tel-00440019
https://tel.archives-ouvertes.fr/tel-00440019
https://tel.archives-ouvertes.fr/tel-00440019/document
https://tel.archives-ouvertes.fr/tel-00440019/file/thesemariasube.pdf

Éditeur(s) : HAL CCSD
Résumé : International audience
In most rock mechanical testing devices, the texture developed during deformation is only observed after the failure, and the detailed mapping of cracks and pore structure evolution, just before or after rupture, remains speculative. Computerized X-ray tomography (CT X-ray) offers a way to observe 'in vivo' some characteristics of a tested sample in the course of its deformation. Therefore we developed an X-ray transparent tri-axial cell that was included in a medical purpose X-ray scanner with a volumetric resolution of the order of 1 mm3. This technique is described and applied to a porous calcarenite, which is regularly scanned for porosity evolution during mechanical testing. The experiment is performed at low confining pressure (2-10 MPa). During testing, an axial load is applied until failure and is then progressively decreased. In these experiments, the peak stress is preceded by phase of diffuse dilatancy. After failure localization, the axial stress is unloaded until the stress reaches isotropy. During this unloading phase, the previous diffuse dilatancy is lost due to an elastic relaxation. Then, the stress is completely relaxed. At this moment the dilatancy increases again and the residual dilatancy is larger than that reached at the peak stress. When observed "post mortem" at microscopic scale, the dilatant structures are comprised of cataclastic deformation bands and cracks in some larger crystals.
International Journal of Rock Mechanics and Mining Science

hal-00767563
https://hal.archives-ouvertes.fr/hal-00767563
DOI : 10.1016/j.ijrmms.2012.07.020

Éditeur(s) : HAL CCSD
Résumé : Geological storage of CO2 is one of diverse technologies being explored to reduce atmospheric carbon fromindustrial processes (i.e. fossil fuel combustion). One of the specific features of CO2 injection is the possibility ofgeochemical reactions (dissolution – precipitation) between mobile reactive brine (e.g. formation water enrichedin CO2) and the host rock during the spatial and temporal evolution of CO2. That leads to modifications in thepore structure, which in turn change the flow dynamics of the reservoir (e.g. the permeability k). Then, thesesstructural modifications can largely control the injectivity, so that the pressure field in the reservoir and also theCO2 propagation. Accordingly, it is crucial to explore the changes in the reservoir properties (e.g. structural andhydrodynamic) induced during a CO2 injection and specially the relationships between them (e.g. k or reactivesurface-Sr versus porosity-φ , k versus rock heterogeneity), for developing predictive modelling tools of thetransport and reaction processes occurring during a CO2 injection and reliable risk assessment. In the case ofcarbonate rocks, the application of the predictive models of transport and reaction is still challenging, because oftheir high heterogeneity so that the incertitude in the reaction kinetics of carbonate minerals.From this perspective, we realized brine-enriched in CO2 percolation experiments through carbonate rocksamples in thermodynamic conditions expected during CO2 injection in deep reservoirs (T = 100°C et P =12MPa). The permeability changes k(t) is monitored during the experiments and the porosity variationφ (t) iscalculated from chemical analyses of the sampled outlet fluids, using ICP-EAS. The pore structure modificationsare investigated from high resolution X ray micro tomography images acquired from the synchrotron ofGrenoble (ESRF). Depending to the dissolution regime, controlled by the reservoir rock fabric and the chemicalcomposition of the brine (e.g. PCO2), we observed that a modification of pore structure can either improve(atypical result in dissolution context) or impair the value of the permeability k.
Le stockage géologique du CO2 est l’une des diverses technologies étant explorées afin deréduire les émissions de carbone atmosphérique des processus industriels (i.e. combustion del’énergie fossile). L’une des spécifiques caractéristiques de l’injection du CO2 en profondeurreste la possibilité de réactions géochimiques (dissolution-précipitation) entre la saumureréactive mobile (e.g. eau de formation enrichie en CO2) et la roche encaissante durantl’évolution spatiale et temporelle du CO2, conduisant à des modifications dans la structure despores et par conséquent dans les propriétés d’écoulement du réservoir (e.g. la perméabilité k).Donc, ces changements structuraux peuvent largement contrôler l’injectivité, ainsi que lechamp de pression dans le réservoir et aussi la propagation du CO2. Il demeure ainsi cruciald’explorer les changement dans les propriétés de réservoirs (e.g. structurales ethydrodynamiques) induits durant une injection de CO2 et explicitement les relations existantesentre eux (e.g. k ou surface réactive-Sr versus porosité-φ , k versus hétérogénéité de la roche),afin de développer des outils de modélisation prédictive des processus de transport etréactionnels se produisant durant une injection de CO2 et d’évaluer de façon fiable les risques.Dans le cas des réservoirs carbonatés, l’application des modèles prédictifs de transport réactifdemeure toujours un enjeu, car contrainte par la forte hétérogénéité en leur sein ainsi que parl’incertitude dans la cinétique de réactions des minéraux carbonatés dans ce contexte. Danscette optique, nous avons réalisé des expériences de percolation à travers des échantillons deroches carbonatées dans les conditions thermodynamiques de stockage en profondeur (T =100°C et P =12 MPa). L’évolution de la perméabilité k(t) est suivie au cours desexpériences ; et la variation de la porosité φ (t) est calculée à partir des résultats d’analyseschimiques au ICP-AES des fluides de sortie échantillonnés. L’investigation des modificationsapportées à la structure des pores est réalisée par le biais de la Micro-Tomographie hauterésolution à rayon X, acquise au synchrotron de Grenoble (e.g. ESRF).Dépendant du régime de dissolution, contrôlé par la fabrique de la roche réservoir et lacomposition chimique de la saumuré chargée en CO2 (e.g. PCO2 engagée), on a observéqu’une modification de la structure de la roche peut soit améliorer soit détériorer (résultatatypique en contexte de dissolution) la valeur de la perméabilité k.
https://hal.archives-ouvertes.fr/tel-01142136

tel-01142136
https://hal.archives-ouvertes.fr/tel-01142136
https://hal.archives-ouvertes.fr/tel-01142136/document
https://hal.archives-ouvertes.fr/tel-01142136/file/thesemangane2013.pdf

Éditeur(s) : HAL CCSD Springer Verlag (Germany) Springer Verlag
Résumé : International audience
The dissolution of carbonate rocks usually leads to both porosity (ϕ) and permeability (k) increase. We present experimental evidences and physical-based models of positive and anti-correlated dynamics of k and ϕ observed during dissolution experiments of carbonate rocks. We study the way the rate of change of ϕ and k is controlled by the degree of undersaturation of the percolating solution for two different types of carbonate rocks. We document the occurrence of an anti-correlated k−ϕ trend when the flowing fluid (deionized water) has a weak capacity of dissolution. A positive correlation is found when CO2 is added to the deionized water to increase the potential dissolution rate. Detailed analyses of the microstructures of the rock performed by X-ray microtomography reveal that low dissolution rate favors detachment of solid particles and their subsequent accumulation at the pore-throat inlet. Particles are detached from the rock matrix due to the differential dissolution rate of the indurated grains and the microporous cement. We then propose a simple phenomenological model to interpret the effect of the pore-throat clogging by the accumulation of partially dissolved carbonate particles. We conjecture that permeability is controlled by the decrease of the effective hydraulic radius and the increase of the tortuosity due to partial and localized obstruction of the pore network. Conversely, increasing the level of undersaturation of the flowing solution leads to an augmented potential of dissolving most of the transported particles before they reach the throats. In this case, both k and ϕ increase and display power-law correlations.
ISSN: 0169-3913

hal-01174145
https://hal.archives-ouvertes.fr/hal-01174145
DOI : 10.1007/s11242-015-0456-2

Éditeur(s) : HAL CCSD Wiley-Blackwell
Résumé : Combined petrographic study and apatite fission track analysis (apatite FTA) across the Gres d'Annot basin document maximum temperatures reached by this turbiditic sandstone formation, from around 60 degrees C at the SW basin margin up to around 200 degrees C below the Penninic frontal thrust, in relation to burial below the front of Alpine nappes. Increasing diagenetic grade across the basin is primarily expressed by the development of silica transfer by pressure solution and correlated porosity loss. We infer the nappe thickness profile, from the nappe front in the SW up to around 8-10 km in the NE. Apatite FTA dates exhumation of the Gres d'Annot during the Late Miocene, in relation to thrusting of the underlying Argentera and Barrot Palaeozoic massifs. This study illustrates the influence of thrust front propagation on foreland basin diagenesis and exhumation, and highlights potential implications for the evolution of sediment reservoir properties in this context.
ISSN: 0954-4879

hal-00411860
https://hal.archives-ouvertes.fr/hal-00411860
DOI : 10.1111/j.1365-3121.2008.00793.x

Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
The Ronda orogenic peridotite (southern Spain) contains a variety of pyroxene-rich rocks ranging from high-pressure garnet granulites and pyroxenites to low-pressure plagioclasespinel websterites. The 'asthenospherized' part of the Ronda peridotite contains abundant layered websterites ('group C' pyroxenites), without significant deformation, that occur as swarms of layers showing gradual modal transitions towards their host peridotites. Previous studies have suggested that these layered pyroxenites formed by the replacement of refractory spinel peridotites. Here, we present a major- and trace-element, and numerical modelling study of a layered outcrop of group C pyroxenite near the locality of Tolox aimed at constraining the origin of these pyroxenites after host peridotites by pervasive pyroxene-producing, refertilization meltrock reactions. Mg-number [=Mg/(Mg + Fe) cationic ratio] numerical modelling shows that decreasing Mg-number with increasing pyroxene proportion, characteristic of Ronda group C pyroxenites, can be accounted for by a melt-consuming reaction resulting in the formation of mildly evolved, relatively low Mg-number melts (similar to 0.65) provided that the melt fraction during reaction and the time-integrated melt/rock ratio are high enough (>0.1 and >1, respectively) to balance Mg-Fe buffering by peridotite minerals. This implies strong melt focusing caused by melt channelling in high-porosity domains resulting from compaction processes in a partial melted lithospheric domain below a solidus isotherm represented by the Ronda peridotite recrystallization front. The chondrite-normalized rare earth element (REE) patterns of group C whole-rocks and clinopyroxenes are convex-upward. Numerical modeling of REE variations in clinopyroxene produced by a pyroxene-forming, melt-consuming reaction results in curved trajectories in the (Ce/Nd)(N) vs (Sm/Yb)(N) diagram (where N indicates chondrite normalized). Based on (Ce/Nd)(N) values, two transient, enriched domains between the light REE (LREE)-depleted composition of the initial peridotite and that of the infiltrated melt may be distinguished in the reaction column: (1) a lower domain characterized by convex-upward REE patterns similar to those observed in Ronda group C pyroxeniteperidotite; (2) an upper domain characterized by melts with strongly LREE-enriched compositions. The latter are probably volatile-rich, small-volume melt fractions residual after the refertilization reactions that generated group C pyroxenites, which migrated throughout the massifincluding the unmelted lithospheric spinel-tectonite domain. The Ronda mantle domains affected by pyroxenite- and dunite- or harzburgite-forming reactions (the 'layered granular' subdomain and 'plagioclase-tectonite' domain) are on average more fertile than the residual, 'coarse granular' subdomain at the recrystallization front. This indicates that refertilization traces the moving boundaries of receding cooling of a thinned and partially melted subcontinental lithosphere. This refertilization process may be widespread during transient thinning and melting of depleted subcontinental lithospheric mantle above upwelling asthenospheric mantle.
ISSN: 0022-3530

hal-00412200
https://hal.archives-ouvertes.fr/hal-00412200
DOI : 10.1093/petrology/egn014

Éditeur(s) : HAL CCSD Wiley
Résumé : Clay shale landscapes are sensitive to landslide, erosion, and re-sedimentation processes. In this context, tectonized clay shales have peculiar hydrological and mechanical behaviours. In order to improve our understanding of the processes involved in such systems, an experimental site has been settled in the Draix Observatory (ORE DRAIX) on a black marl hill slope of the Southern Alps (France) in the framework of the ECOU-PREF project. The site is a natural laboratory to study the evolution of clay shale landscapes at several scales (regional to µm). In this study, we aim to characterize the internal structure and fissure patterns of a stable interfluve, in order to locate preferential water flows within the system, and anticipate its evolution. This work is based on a series of mutli-disciplinary approaches including petrophysical analyses, well pulse injection tests and downhole geophysical measurements. Borehole geophysical results were combined with laboratory measurements on core plugs (permeability, density, porosity, and acoustic velocity). Optical and acoustical images have been used as an original tool for internal discontinuities characterisation and potential active flow path detection. They allowed the identification of three main lithological units interpreted as several stages of shale alteration. In addition, several main structural plane discontinuities (open fractures, schistosity planes, and fractures infilled with calcite or clays) were identified from the images and their potential transmissivity discussed with regard to piezometric and tracer measurements. In all, the integration of measurements leads to propose a simple scenario of fluid circulation and chemical alteration of the interfluve.
ISSN: 0885-6087

hal-00757581
https://hal.archives-ouvertes.fr/hal-00757581
DOI : 10.1002/hyp.7997

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
Torsion experiments (inline image =3 × 10−4 s−1) were performed to investigate the large strain (γmax = 15) rheology on quartz-muscovite aggregate as analogue to pelitic rocks undergoing melting and crystallization during deformation at 300 MPa confining pressure and 750°C temperature. Microstructures reveal four distinct but gradational stages of crystal-melt interactions during deformation--(a) solid state deformation, (b) initiation and domination of partial melting, (c) simultaneous partial melting and crystallization, and (d) domination of crystallization. The microstructural stages are linked to the rheology of the deforming samples. Partial melting starts at relatively low finite shear strains (γ = 1-3) showing approximately 60% strain softening. At γ = 4-10 the partially molten bulk material shows a steady state flow at low stress. Further crystallization of new crystals at the expense of melt between γ = 10 and 15 causes weak strain hardening until the material fails by developing brittle fractures. The stress exponent (n), calculated at γ = 1, 5, and 10, increases from ∼ 3 to ∼ 43, indicating a transition from power to power law breakdown or exponential flow of the bulk system. Hydrostatic experiments for equivalent times and conditions of the torsion experiments were also conducted to evaluate the reaction kinetics and microstructures under static conditions. The new experimental data establish that partially molten rock does not flow according to a constant strain rate-dependent power law (steady state) rheology. The rheological transition from strain rate sensitive to strain rate insensitive flow is interpreted as a function of melt-crystal ratio, their mutual interactions, and the evolution of microstructures in the partially molten rock.
ISSN: 0148-0227

hal-01053709
https://hal.archives-ouvertes.fr/hal-01053709
DOI : 10.1002/2013JB010777