Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
A set of four reactive flow-through experiments at temperature T = 100 degrees C and total pressure P=12 MPa was performed in limestone reservoir samples. By using various ranging from 0.7 to 10 MPa, these experiments mimic mass transfers occurring (1) near the injection well, where the brine is almost saturated with CO2 (i.e. P-CO2 approximate to P), and (2) at increasing distances from the injection well, where the fluid displays lower values and higher divalent cation concentrations due rock dissolution along the fluid pathway. Results for P-CO2 = 10 MPa show non-uniform dissolution features associated with transport-controlled mass transfer, while reaction-controlled uniform dissolution is observed for P-CO2 = 2.5 MPa. The experiment with P-CO2 = 6 MPa allows investigating in detail the transition from transport-to reaction-controlled dissolution. Conversely, the experiment reproducing conditions far from the injection well (P-CO2 = 0.7 MPa), shows a decrease of porosity triggered by the precipitation of Mg-rich calcite. For all the dissolution experiments, the time-resolved porosity phi(t) can be modeled by a simple non-linear equation including parameters that characterise the dissolution regime triggered by the reactivity of the inlet fluid (measured by the Damkohler number, Da). Furthermore, all dissolution experiments display power scaling between permeability (k) and porosity (phi) with distinctly different scaling exponents characterising the reactivity of the fluid percolating the sample, independently from the decrease with time of the reactive surface area. It is shown also that dissolution at moderate positive values of Da seems the most efficient to increase permeability and promote a rapid spreading of the reaction front, while inducing minimal modification of the porosity in the vicinity of the CO2 injection well. These results can be used to parameterize the k-phi function for modeling the earliest dissolution processes occurring in the vicinity of the reaction front.
ISSN: 0009-2541

hal-00445277
https://hal.archives-ouvertes.fr/hal-00445277
DOI : 10.1016/j.chemgeo.2009.03.028

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
Résumé : This study provides additional constraints on the relations between deformation, hydration and percolation of fluids and melts in the subcontinental lithospheric mantle beneath a craton and a rift, as well as their implication on its geodynamical behaviour. I have analysed the microstructures, the CPOs, and the hydrogen content of mantle xenoliths from the Kaapvaal craton, and two sets of xenoliths from different localities along the East African Rift (North Tanzanian Divergence and SE Ethiopia).The coarse-granular microstructures and the well-defined CPOs in Kaapvaal peridotites suggest a deformation followed by a long quiescence time. Orthorhombic olivine CPOs predominates, but axial-[100] and axial-[010] are also measured. Cratonic peridotites record multiple metasomatic episodes, leading to a significant compositional heterogeneity, which cannot be imaged by seismic studies. Olivine hydrogen contents are variable, but tend to increase until 150 km depth, reaching up to 50 ppm wt. H2O. The deeper samples are almost dry. Piston-cylinder experiments on hydrogen diffusion between a volatile-rich kimberlitic melt and forsterite suggest that the presence of CO2 in the system could significantly decrease water fugacity and thus forsterite hydration. These experimental results indicate that the hydrogen contents measured in olivine were acquired during a metasomatic event rather than during xenolith extraction by kimberlites. However, this metasomatism was not followed by remobilization of the cratonic root.In the North Tanzanian Divergence, localities within the rift axis and the volcanic transverse belt (Lashaine and Olmani) show significant differences in microstructures and olivine CPO patterns. In Lashaine, coarse-granular microstructures and orthorhombic to axial-[100] CPO patterns in olivine can be explained by transpressional deformation during the formation of the Mozambique belt, or by the occurrence of a remnant of a cratonic domain embedded within the Mozambique belt. Within the rift axis, porphyroclastic to mylonitic microstructures suggest a recent rift-related deformation accompanied by syn-kinematic melt-rock reactions, and followed by variable annealing. The strong heterogeneity in microstructures and olivine CPO suggests that this deformation was acquired during multiple tectonic events probably linked to episodic magma percolation, separated by quiescence episodes. The axial-[100] patterns in olivine and the oblique fast directions reported by SKS studies are coherent with transtensional deformation within the lithospheric mantle beneath the rift.The peridotites from SE Ethiopia are less recrystallized than the rift-axis Tanzanian peridotites, displaying coarse-porphyroclastic microstructures. Microstructures and orthorhombic CPOs in olivine suggest syn- to post-metasomatic deformation. S-waves polarization anisotropies calculated for these samples cannot explain alone the delay times reported by SKS studies in this part of the East-African Rift.
Les travaux réalisés durant cette thèse apportent de nouvelles contraintes sur les relations entre déformation, hydratation et percolation de fluides et/ou de magmas dans le manteau subcontinental sous un craton et sous un rift, et leurs implications sur son comportement rhéologique. Il repose sur l'analyse des microstructures, des OPRs et des teneurs en hydrogène de xénolites mantelliques du craton du Kaapvaal, et sur deux séries de xénolites provenant de différentes localités le long du rift Est-Africain (Divergence Nord Tanzanienne et SE de l'Ethiopie). Les microstructures granulaires à gros grains et les OPRs bien définies des péridotites du craton du Kaapvaal sont cohérentes avec un épisode de déformation suivi d'une longue période de quiescence. Les OPRs de l'olivine sont majoritairement à symétrie orthorhombique, mais des symétries axiale-[100] et axiale-[010] sont aussi mesurées. Les péridotites cratoniques enregistrent de multiples épisodes métasomatiques, ayant entraîné une hétérogénéité de compositions à petite échelle ne pouvant être détectée par les études sismiques. Les teneurs en hydrogène mesurées dans l'olivine sont variables, mais ont tendance à augmenter jusqu'à 150 km de profondeur, atteignant alors jusqu'à 50 ppm wt. H2O. En dessous de cette profondeur, les échantillons montrent des teneurs en hydrogène très faibles. Les expériences réalisées en piston-cylindre sur la diffusion de l'hydrogène issue d'un liquide kimberlitique vers de la forstérite suggèrent que la fugacité en eau pourrait fortement être diminuée par la présence de CO2, empêchant l'hydratation de l'olivine durant extraction des xénolites par les kimberlites. Ces résultats expérimentaux suggèrent que les teneurs en hydrogène dans l'olivine des péridotites du craton du Kaapvaal ont été acquises durant un épisode métasomatique en profondeur et non pendant leur extraction par les kimberlites. Ces teneurs n'ont toutefois pas à ce jour entraîné de remobilisation de la racine cratonique. Enfin, le calcul des propriétés sismiques des péridotites cratoniques révèle que les anisotropies générées par les OPRs de ces échantillons sont suffisantes pour expliquer les anisotropies mesurées par les ondes SKS et les ondes de surface.Les xénolites de la Divergence Nord-Tanzanienne, montrent des variations significatives de microstructures et d'OPR de l'olivine entre les péridotites des localités dans l'axe du rift et celles de la chaîne volcanique transverse (Lashaine et Olmani). A Lashaine, les microstructures granulaires à gros grains et les OPRs de type orthorhombique et axial-[010] peuvent être expliquée par une déformation en transpression liée à la formation de la chaîne Mozambique ou par la présence d'une relique d'un domaine cratonique à l'intérieur de la chaîne Mozambique. Dans l'axe du rift, les microstructures porphyroclastiques à mylonitiques suggèrent une déformation plus récente, accompagnée de réactions magma-roche sous des conditions proches du solidus, suivie d'un recuit variable. L'hétérogénéité des microstructures enregistrées par les échantillons du rift suggère de multiples épisodes de déformation localisée, probablement liés à l'injection percolation épisodique de magmas, espacés de périodes d'accalmie. Les OPRs de l'olivine de type axial-[100] et l'orientation des directions de polarisation des ondes SKS suggère que le rift s'est formé en régime de transtension Les péridotites du Sud-Est de l’Éthiopie présentent des microstructures porphyroclastiques à gros grains moins recristallisées qu'en Tanzanie. Les microstructures et les OPRs principalement de type orthorhombique suggèrent une déformation syn- à post-métasomatisme. Les anisotropies de polarisation des ondes S calculées pour ces échantillons sont insuffisantes pour expliquer à elles seules les déphasages des ondes SKS dans cette partie du rift.
https://tel.archives-ouvertes.fr/tel-01684759

Droits : info:eu-repo/semantics/OpenAccess
NNT : 2014MON20139
tel-01684759
https://tel.archives-ouvertes.fr/tel-01684759
https://tel.archives-ouvertes.fr/tel-01684759/document
https://tel.archives-ouvertes.fr/tel-01684759/file/43443_BAPTISTE_2014_archivage_cor.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Underground CO2 sequestration is highly recommended as an effective means of significantly decreasing CO2 concentration in the atmosphere. Mineral storage is the more secure technology, but requires the presence of high concentration of divalent cations in the pore-fluid. Results from CO2 percolation experiments through chlorite/zeolite-rich sandstone samples from the Pretty Hill Formation (Otway Basin, Australia) are presented. The dissolution of the laumontite (7 wt.%) and chamosite (7 wt.%) are the potential sources of calcium, iron and magnesium required for carbonate precipitation. The percolation experiment was setup to reproduce, at laboratory scale, the in situ temperature and pressure conditions (T = 95 degrees C and P = 10 MPa). The fluid injected at constant flow rate is a rock-equilibrated brine subsequently enriched in CO2 up to partial pressure of 6 MPa. We observe feldspars, laumontite and chamosite dissolution, kaolinite and silica precipitation and a noticeable sink of CO2 in the sample which is attributed to the precipitation of both amorphous carbon due to the reduction of CO2 and Fe-rich carbonate. Permeability decreases of about one order of magnitude due to the localization of the kaolinite precipitation in the main flow paths, while porosity increases. The high reactivity of this sandstone makes this reservoir a valuable target for CO2 mineralization, but the associated permeability decrease may limit the injection rate and the spreading of the CO2 in the reservoir.
ISSN: 0009-2541

hal-00712829
https://hal.archives-ouvertes.fr/hal-00712829
DOI : 10.1016/j.chemgeo.2011.11.018

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We report chlorine (Cl) and fluorine (F) abundances in minerals, interstitial glasses, and melt inclusions in 12 andesite-hosted, spinel harzburgite xenoliths and crosscutting pyroxenite veins exhumed from the sub-arc lithospheric mantle beneath Avacha volcano in the Kamchatka Arc (NE Russia). The data are used to calculate equilibrium mineral-melt partition coefficients (Dmineral/meltDmineral/melt) for Cl and F relevant to subduction-zone processes and unravel the history of volatile depletion and enrichment mechanisms in an arc setting.Chlorine is ∼100 times more incompatible in pyroxenes (View the MathML sourceDClmineral/melt = 0.005–0.008 [±0.002–0.003]) than F (View the MathML sourceDFmineral/melt = 0.50–0.57 [±0.21–0.24]), which indicates that partial melting of mantle sources leads to strong depletions in Cl relative to F in the residues. The data set in this study suggests a strong control of melt composition on View the MathML sourceDCl,Fpyroxene/melt, in particular H2O contents and Al/(Al + Si), which is in line with recent experiments. Fluorine is compatible in Ca-amphibole in the ‘wet’ sub-arc mantle (View the MathML sourceDFamphibole/melt = 3.5–3.7 [±1.5]) but not Cl (View the MathML sourceDClamphibole/melt = 0.03–0.05 [±0.01–0.03]), indicating that amphibole may fractionate F from Cl in the mantle wedge. The inter-mineral partition coefficients for Cl and F in this study are consistent amongst different harzburgite samples, whether they contain glass or not. In particular, disseminated amphibole hosts much of the Cl and F bulk rock budgets of spinel harzburgites (View the MathML sourceDClamphibole/pyroxene up to 14 and View the MathML sourceDFamphibole/pyroxene up to 40). Chlorine and fluorine are variably enriched (up to 1500 ppm Cl and 750 ppm F) in the parental arc picrite and boninite melts of primitive pyroxenite veins (and related melt inclusions) crosscutting spinel harzburgites.Based on the data in this study, the main inferences on the behaviour of Cl and F during melting and metasomatic processes in the sub-arc mantle are as follow:(i) Melting models show that most depleted mantle protoliths of intra-oceanic arc sources can have extremely low Cl/F (0.002–0.007) before being overprinted by subduction-derived components.(ii) Chlorine has a higher percolation distance in the mantle than F. Even for small fluid or melt volumes, Cl and F signatures of partial melting are overprinted by those of pervasive percolation, which increases Cl/F in percolating agents and bulk peridotites during chromatographic interaction and/or amphibole-forming metasomatic reactions. These processes ultimately control the bulk Cl and F compositions of the residual mantle lithosphere beneath arcs, and likely in other tectonic settings.(iii) Fluxed melting models suggest that Cl enrichment in arc picrite and boninite melts in this study, and in many arc melt inclusions reported in the literature, could be related to the infiltration of high Cl/F fluids derived from subducted serpentinite or altered crust in mantle wedge sources. However, these high Cl/F signatures should be re-evaluated with new models in light of the possible overprint of pervasive percolation effects in the mantle. The breakdown of amphibole (and/or mica) in the deep metasomatised mantle at higher pressure and temperature conditions than in the slab may explain, at least in part, the positive correlations between F abundances and Cl/F in primitive arc melt inclusions and slab depth.
ISSN: 0016-7037

hal-01553610
https://hal.archives-ouvertes.fr/hal-01553610
DOI : 10.1016/j.gca.2016.10.035

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Heletz sandstone (Israel) reactivity is studied by means of CO2-rich brine percolation experiments and modeling. Experiments are performed at in situ temperature and pressure conditions with two distinctly different injection flow rates and for two different brine compositions: the genuine Heletz brine and a similar brine but in equilibrium with gypsum. The Heletz sandstone is composed of quartz, dolomite, ankerite, K-feldspar, clay minerals and minor amounts of gypsum and pyrite. The main reaction is the dissolution of the carbonates which is fastest for the highest flow rate injection and for the genuine Heletz brine. Permeability increases during the five percolation experiments, regardless of flow rate and brine type. This increase in permeability is associated to a decrease in porosity during the gypsum-equilibrated brine experiments due to gypsum precipitation. The precipitation of secondary minerals (kaolinite, muscovite and smectite) is mainly controlled by the dissolution of K-feldspar and largest at low flow rate injection, indicating that these precipitation processes are diffusion-controlled and localized in immobile zones where favorable chemical micro-environments exist. These processes are quantified by means of a reactive transport model. These results indicated that the CO2 injection at the Heletz site should trigger both permeability increase in interface between brine and CO2, which may extend over a large extension and where mixing processes are very active, especially near the well under intermittent injection conditions.
ISSN: 1750-5836

hal-01356329
https://hal.archives-ouvertes.fr/hal-01356329
DOI : 10.1016/j.ijggc.2015.10.023

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
To test the impact of fluid flow on the reactivity of porous (ultra-)mafic rocks, reactive percolation experiments were realized during which CO2-enriched water was injected at two different injection rates (Q = 0.1 and 1 mL h−1) through sintered analogues of olivine-accumulation zones in basaltic flows at temperature and fluid composition conditions (T = 180 °C; NaHCO3 buffered solution) favorable for CO2-mineralization (carbonation).All experiments resulted in silicate dissolution, carbonate precipitation upstream and (proto-)serpentine formation downstream indicating a decrease in the fluid reactivity along flow paths. The measured bulk carbonation rates ranged from 4 to 7 × 10−8 s−1; these values were significantly lower than previously published values of olivine carbonation rate obtained on powders in closed batch and flow-through reactors. Our study show complex couplings, at pore scale, between fluid flow, localization of reaction zones, and chemical reaction kinetics which in turn control hydrodynamic properties, carbonation rate and efficiency and fluid reactivity. This results in carbonation rates being higher when injection rates are high and permeability ultimately controlling carbonation reactions by limiting fluid input. During experiments, notable changes in permeability occurred for only minor changes in porosity indicating a control by the geometry of the porous network: heterogeneities in the distribution of flow paths favored the localization of precipitated minerals which in turn resulted in the closure of flow paths. This mechanism was particularly efficient at low injection rates. These results imply that controlling the injection rate could allow enhancing/limiting the efficiency of in situ carbonation.
ISSN: 0883-2927

hal-01115284
https://hal.archives-ouvertes.fr/hal-01115284
DOI : 10.1016/j.apgeochem.2014.11.024

Éditeur(s) : HAL CCSD
Résumé : In coastal carbonate aquifers submitted to a saline intrusion, water - rock interactions processes at the interface between freshwater and saltwater are a cause for heterogeneities development within the porous media. The dissolutions and precipitations induced by the mixing zone play a major role in the transport properties of the reservoir and so in the long term evolution of the saltwater intrusion. The characterization and the in situ observation of a current saline intrusion in the Llucmajor carbonate platform at the experimental site of Ses Sitjoles (South-Easth of Mallorca Island, Spain), allowed to study the temporal evolution of the saltwater intrusion and the biogeochemical processes active in the mixing zone. The influence of microstructure, characterized using X-Ray microtomography, on the petrophysical and flow properties was investigated in laboratory and flow-through experiments were also conducted to study the modifications of the microstructures when submitted to water - rock interactions processes. The mixing zone at the Ses Sitjoles site appears as quite thick and not very sensitive to climate and anthropic stress and is proved to be the locus of active microbiological activity. Laboratory studies highlight a strong control of the microporosity on transport processes and of pCO2 on water - rock interactions. The percolation experiments of slightly reactive waters reveal calcite dissolution together with a decrease in permeability due to a rearrangement of micro-grains within the microporous network.
Les processus d'interactions fluide-roche à l'interface eau douce-eau salée, dans les aquifères carbonatés côtiers soumis à une intrusion saline, sont une des causes du développement d'hétérogénéités dans la structure du milieu poreux. Les dissolutions et/ou précipitations engendrées par la présence de cette zone de mélange jouent un rôle déterminant pour les propriétés de transport du réservoir et donc l'évolution à long terme de l'intrusion d'eau salée. En prenant l'exemple de la plateforme carbonatée de Llucmajor au niveau du site expérimental de Ses Sitjoles (Sud-Est de Majorque, Espagne), un travail de caractérisation et d'observation in situ à moyen terme de l'intrusion saline actuelle de ce réservoir permet de décrire son évolution temporelle et les processus biogéochimiques actifs dans la zone de mélange. L'influence de la microstructure du milieu poreux, caractérisée par microtomographie RX, sur les propriétés pétrophysiques et hydrodynamiques est étudiée en laboratoire et des expériences de percolations d'eaux réactives (mélanges eau douce - eau salée et eau pure chargée en CO2) sont réalisées afin d'étudier les modifications de ces microstructures lorsqu'elles sont soumises à des interactions eau - roche. La zone de mélange eau douce - eau salée rencontrée au niveau du site de Ses Sitjoles est large et peu sensible aux contraintes extérieures (climatologiques et anthropiques) et constitue un lieu d'activité microbiologique particulièrement actif. En laboratoire, on observe un fort contrôle des phénomènes de transport par la microporosité et des processus d'interactions eau - roche par la pCO2. Dans le cas d'une percolation de fluides moyennement réactifs, les expériences mettent en évidence une dissolution de calcite accompagnée par une diminution de la perméabilité, liée à un réarrangement des micro-grains à l'intérieur du réseau microporeux.
https://tel.archives-ouvertes.fr/tel-00767152

tel-00767152
https://tel.archives-ouvertes.fr/tel-00767152
https://tel.archives-ouvertes.fr/tel-00767152/document
https://tel.archives-ouvertes.fr/tel-00767152/file/thesegaring.pdf

Éditeur(s) : HAL CCSD
Résumé : The main purpose of this thesis was to characterize and to model the hydrodynamic and thermochemical processes leading to the alteration of the wellbore cement materials under borehole conditions. Percolation experiments were performed on fractured cement samples under CO2 storage conditions (60°C and 10MPa). Injection flow rate was dictated by the fracture aperture of each sample. CO2 enriched brine was flowed along the fracture aperture, and permeability changes as well as chemical evolution of major cations were continuously acquired during the experiment time. Reaction paths developed by the alteration of the cement were characterized using microtomography and ESEM images. The experiments conducted using samples presenting large fracture apertures during 5h showed that permeability was maintained constant during the experiment time. Three reacted layers were displaying by the alteration of portlandite and CSH. Long term experiment (26h) conducted with large initial fracture aperture showed a decrease of the permeability after 15hours of CO2 exposure. Otherwise, experiments performed on samples presenting narrow apertures indicated the conversion of portlandite and CSH to calcite leading to the permeability reduction and the fracture clogging. Assemblages of phases and chemical changes were modelled using GEMS-PSI speciation code. We studied also using a coupled transport-reactive model the conditions leading to the cement alteration and the formation of associated layers.
L'objectif de cette thèse était de modéliser à partir des expériences de percolation-réactive, les processus hydrodynamique et réactionnel qui gouvernent l'altération des ciments de puits. Différentes expériences ont été réalisées dans des conditions représentatives de celles du stockage du CO2. Des échantillons fracturés ont été utilisés pour injecter une saumure enrichie en CO2 à 60°C et 10MPa et à différentes pressions partielles de CO2. Le débitd'injection variait en fonction des propriétés hydrauliques de l'échantillon exposé. L'injection d'une saumure enrichie en CO2 à débit constant à travers une fracture supposée plane a permis d'étudier les modifications des propriétés hydrodynamiques et ces conséquences sur la géochimie et la microstructure du ciment altéré. L'impact dynamique de l'évolution microstructurale a été mis en évidence. Les expériences conduites sur des échantillons présentant de larges ouvertures, réalisées sur une durée de 5 h, ont montré que la perméabilité était maintenue constante le long de l'expérience. Trois couches d'altération se sont développées consécutivement à la dissolution de la portlandite et la décalcification des CSH. L'altération a entrainé la précipitation des carbonates et de la silice amorphe à proximité de la fracture. Dans le cas d'une expérience longue durée appliquant les mêmes conditions que précédemment on a observé que la croissance de la silice amorphe a entrainé la diminution de la perméabilité. Par ailleurs les expériences effectuées sur des échantillons présentant de faibles ouvertures, ont indiqué que la conversion de la portlandite en calcite conduit au colmatage de la fracture. L'évolution des assemblages de phases conduisant à la formation des carbonates et de la silice amorphe a été modélisée à partir du code géochimique GEMS. Les mécanismes de diffusion et les processus de mise en place des couches d'altération ont été étudiés à partir d'un modèle analytique et d'un modèle de transport réactif à partir du code géochimique PHREEQC.
https://tel.archives-ouvertes.fr/tel-01038034

tel-01038034
https://tel.archives-ouvertes.fr/tel-01038034
https://tel.archives-ouvertes.fr/tel-01038034/document
https://tel.archives-ouvertes.fr/tel-01038034/file/theseabdoulghafour.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We studied the deformation in a partially molten mantle through detailed petrostructural analysis of plagioclase lherzolites from the northwestern part of the central Lanzo massif. These peridotites display a pervasive anastomosed network of millimetre to centimetre-scale plagioclase-rich bands, which grades locally into a planar layering marked by an intercalation of plagioclase-rich and olivine-rich layers up to tens of centimetres wide. Both the anastomosed and the planar layering are subparallel to the deformation fabric, characterized by a foliation defined by the shape-preferred orientation of olivine and by crystal preferred orientation (CPO) of olivine, orthopyroxene, and clinopyroxene. This parallelism, the coexistence of microstructural evidence for melt-rock reactions and for deformation by dislocation creep, and the predominance of axial-[010] olivine CPO patterns, characterized by [010] axes clustered normal to the layering, indicate that deformation and the reactive melt percolation that formed the layering were coeval. Strong heterogeneity in mineral composition in the planar layering domains, with Fe-enrichment in olivine and spinel and highly variable Ti content in spinel in cm-scale plagioclase-rich bands, implies that the latter interacted with higher melt volumes. High Ti contents in pyroxenes and spinel in the anastomosed layering domains point to changes in melt composition, hinting to less effective melt transport. We propose therefore that the planar layering records melt segregation in layers parallel to the shear plane, whereas the anastomosed layering results from melt alignment along grain boundaries subparallel to the shear plane, without segregation. Finite strain in the different layers cannot be quantified, but comparison of the present observations with data from experiments and from other mantle outcrops displaying shear-controlled melt organization suggests that the transition from the anastomosed to the planar layering might record an increase in finite strain, that is, strain localization associated with variations in the instantaneous melt fraction.
ISSN: 0040-1951

hal-01053509
https://hal.archives-ouvertes.fr/hal-01053509
DOI : 10.1016/j.tecto.2014.01.007

Éditeur(s) : HAL CCSD American Chemical Society
Résumé : International audience
Carbonation of ultramafic rocks in geological reservoirs is, in theory, the most efficient way to trap CO2 irreversibly; however, possible feedback effects between carbonation reactions and changes in the reservoir permeability must be considered to realistically assess the efficiency and sustainability of this process. We investigated changes in the hydrodynamic properties of sintered dunite samples by means of percolation experiments, under conditions analogous to that of in situ carbonation. Our results show that carbonation efficiency is controlled by the local renewal of the reactants and the heterogeneity of the pore structure. Preferential flow zones are characterized by the formation of magnetite and of a silica-rich layer at the olivine surfaces, which eventually inhibits olivine dissolution. Conversely, sustainable olivine dissolution together with coprecipitation of magnesite, siderite, and minor Mg-TOT-phyllosilicates, occur in reduced-flow zones. Thus carbonate precipitation only decreases porosity in zones where diffusion-controlled transport is dominant. Consequently, while high flow rates will decrease the carbonation efficiency of the reservoir and low flow rates may reduce the permeability irreversibly close to the injection point, moderate injection rates will ensure a partial carbonation of the rock and maintain the reservoir permeability.
ISSN: 0013-936X

hal-00424540
https://hal.archives-ouvertes.fr/hal-00424540
DOI : 10.1021/es8018429

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