Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Random walk (RW) methods are recurring Monte Carlo methods used to modelconvective and diffusive transport in complex heterogeneous media. Many applications canbe found, including fluid mechanic, hydrology and chemical reactors modeling. These methodsare easy to implement, very versatile and flexible enough to become appealing for manyapplications because they generally overlook or deeply simplify the building of explicit complexmeshes required by deterministic methods. RWprovides a good physical understandingof the interactions between the space scales of heterogeneities and the transport phenomenaunder consideration. In addition, they can result in efficient upscaling methods, especiallyin the context of flow and transport in fractured media. In the present study, we review theapplications of RW to several situations that cope with diverse spatial scales and differentinsights into upscaling problems. The advantages and downsides of RW are also discussed,thus providing a few avenues for further works and applications.
ISSN: 0169-3913

insu-01308060
https://hal-insu.archives-ouvertes.fr/insu-01308060
DOI : 10.1007/s11242-016-0693-z

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
GenMol (TM) code is used to simulate Atomic Force Microscopy (AFM) tests at a kaolinite/brine/kaolinite contact, the confined fluid in sub-nanometre interspaces being in equilibrium with an external multi-species solution. The attraction/repulsion effort, i.e. the derivative versus the interspace aperture h of the interaction energy between both kaolinite faces, is computed versus the variable composition of the confined fluid (see for the method Part I of this work). Two external solutions are tested. Solution Si is a neutral brine (pH=7.5) leading to a possible attraction for apertures lower than 7 angstrom. Solution S2 is an acidified brine (pH=3.2) leading to repulsion whatever may be the aperture h. These two AFM simulations prove the existence of a critical pH value (3.2 < pH(crit) < 7.5) of the external solution, below which the acidification of a natural brine in a CO2 confinement inhibits adhesion between kaolinite aggregates.
ISSN: 0022-0248

hal-00544678
https://hal.archives-ouvertes.fr/hal-00544678
DOI : 10.1016/j.jcrysgro.2010.08.012

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
We study diffusion in a heterogeneous medium that is characterized by spatially varying diffusion properties from a random walk point of view. We show that an inhomogeneous continuous time random walk (CTRW) with a spatially variable exponential transition time distribution solves the spatially discretized heterogeneous diffusion equation. This demonstrates the equivalence of the widely used time-domain random walk (TDRW) scheme and spatially inhomogeneous CTRW and at the same time provides a demonstration of the formal equivalence of the TDRW particle formulation and the heterogeneous diffusion equation. Based on this equivalence, we develop a TDRW method for heterogeneous diffusion under spatially variable multirate mass transfer properties. We discuss the implementation of these schemes and study the diffusion behavior in the presence of traps that are characterized by a truncated power-law trapping time distribution.
ISSN: 0309-1708

hal-00767566
https://hal.archives-ouvertes.fr/hal-00767566
DOI : 10.1016/j.advwatres.2012.07.015

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 American Geophysical Union
Résumé : International audience
We aim at testing and validating a mobile-immobile mass transfer model from a set of single-well injection withdrawal tracer tests in a heterogeneous porous aquifer. By varying the duration of the injection phase, different volumes of aquifer are investigated by the tracer. Hence, we focus the transport model validation not only on reproducing a single breakthrough curve (BTC) but also on the model's capacity to predict the amount of mixing as a function of the volume visited by the tracer. All the BTCs are strongly asymmetric, as expected when dispersion is controlled by diffusive mass transfers between the mobile water and the immobile water part of the porosity. However, the BTC cannot be modeled by a conventional mobile-immobile mass transfer model with a simple power law memory function. To account for that, we implement a continuous time random walk model in which the transition time distribution y (t), which is related to the excursion time probability of the tracer in the immobile domain, is a dual-slope power law distribution. The model best fits the BTC data set with a transitional regime controlled by y(t) t2 and an asymptotic regime characteristic of the conventional double-porosity model with y(t) t1.5 . This work emphasizes that high-resolution concentration measurement and multiple-scale tracer tests are required for assessing solute dispersion models in heterogeneous reservoirs and for subsequently obtaining reliable predictions.
ISSN: 0043-1397

insu-00373698
https://hal-insu.archives-ouvertes.fr/insu-00373698
https://hal-insu.archives-ouvertes.fr/insu-00373698/document
https://hal-insu.archives-ouvertes.fr/insu-00373698/file/Borgne_et_al-2008-Water_Resources_Research.pdf
DOI : 10.1029/2007WR006279

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
We derive a general formulation of the time domain random walk (TDRW) approach to model the hydrodynamic transport of inert solutes in complex geometries and heterogeneous media. We demonstrate its formal equivalence with the discretized advection-dispersion equation and show that the TDRW is equivalent to a continuous time random walk (CTRW) characterized by space-dependent transition times and transition probabilities. The transition times are exponentially distributed. We discuss the implementation of different concentration boundary conditions and initial conditions as well as the occurrence of numerical dispersion. Furthermore, we propose an extension of the TDRW scheme to account for mobile-immobile multirate mass transfer. Finally, the proposed TDRW scheme is validated by comparison to analytical solutions for spatially homogeneous and heterogeneous transport scenarios.
ISSN: 0043-1397

hal-01356319
https://hal.archives-ouvertes.fr/hal-01356319
DOI : 10.1002/2015WR018511

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Several studies, both theoretical and experimental, show that sedimentary rocks have fractal pore-grain interface. The real rocks are 3-d structures with highly tortuous and often fractal pore spaces. Before attempting simulation of this daunting geometry, we present here, as a preliminary study, a simpler 2-d version. In this paper, a computer simulated 2-d sedimentary rock structure is generated by the relaxed bidisperse ballistic deposition model. Grains of two different sizes are dropped ballistically on a linear substrate. By changing the fraction of the two types of particles, the porosity of the rock structure can be tuned. The structure undergoes compaction through the relaxation of possible unstable overhangs. The micro structure of the pore space is investigated. The pore mass and the rock-pore interface show a fractal behaviour with the same fractal dimension indicating that the pore volume is a fractal. Our simulation results indicate that the process of compaction of grains during the deposition process seems to erase the dependency of the fractal dimension on the grain size distribution. The two point density correlation is measured for the pore space. It shows anisotropy which is an outcome of the growth rule. X-ray tomography of two-dimensional sections of real sedimentary rocks obtained from Mallorca Island is subjected to the same study and the results compared with those obtained from simulation. The simulation results agree qualitatively with the real rock sample. We also study diffusion on the pore space. Diffusion is found to be anomalous as is expected in fractal spaces. It also bears the signature of anisotropy of the structure. Diffusion studies on the real rock sample could not yield conclusive results as the system size is not large enough.
ISSN: 0926-9851

hal-00761818
https://hal.archives-ouvertes.fr/hal-00761818
DOI : 10.1016/j.jappgeo.2012.09.002

Éditeur(s) : HAL CCSD
Résumé : International audience
The injection of reactive mineral suspensions is a possible process to either reinforce or seal wells in geologic carbon sequestration sites. Among others, olivine slurries could be used as CO2-triggered cements, as they carbonate under the thermodynamic conditions of deep storage. However, injection of such slurries requires to control their initial fluidity and its evolution during the displacement. For this purpose, we have characterized the rheological evolution of olivine suspensions, of particle sizes 1−10 μm, sheared at 100 s−1, in the ranges of 10−40% for the volume fractions, 20−50 bars for the CO2 pressure, and 60-110°C for the temperature. The apparent viscosity, measured at 100 s−1, increases exponentially, with a characteristic time ranging from less than 1 h to more than 10 h, and decreasing with olivine concentration, CO2 pressure, and temperature. Moreover, a careful characterization of the slurry rheology carried out in the initial stages of slow evolution, shows that the slurry obeys a Bingham plastic law, with a yield stress ΣB, and a Bingham viscosity µB increasing from 1 to 20 Pa and from 4 to 110 mPa s, respectively, when the olivine volume fraction φ is increased from 10 to 30%. Such variations can be accounted by classical models (Wildemuth and Williams [1984]: Rheologica Acta, 23,627-635, Krieger [1972]: Advances in Colloid and Interface Science, 3, 111-136).
Environmental Progress & Sustainable Energy

hal-01054131
https://hal.archives-ouvertes.fr/hal-01054131
DOI : 10.1002/ep.11826

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Saline aquifers in deep sedimentary formations are considered the primary candidates for geological storage of CO2, due to their large volumetric capacity that would be sufficient to meet the needs for CCS storage space in a global scale. In comparison to depleted oil and gas reservoirs the deep saline aquifers are, however, less investigated as there has previously been little economic interest in them. Effective methods for characterizing the storage aquifers are crucial for a successful implementation of any CCS project and therefore being developed and transferred from other applications in a various CCS projects.The objective of EU FP7 funded project MUSTANG project (A multiple space and time scale approach for the quantification of deep saline formations for CO2 storage, www.co2mustang.eu) has been to develop methods for characterizing saline aquifers and for understanding their properties. An essential part of this was establishment of a CO2 injection site at Heletz, Israel, where small-scale scientifically motivated injection experiments are planned to be carried out in presently ongoing continuation projects TRUST (http://trust-co2.org/) and CO2QUEST (www.co2quest.eu).While a large number of publications has been already produced based on the work in the MUSTANG project and its successors, and published in different journals, including this one, the objective of this Special Edition has been to gather some of the concluding work in the same journal issue. The focus has in particular been in summarizing the site characterization work carried out at the Heletz site, thereby providing readers an easy overview of the findings and characteristics of the site. In addition, some related work from some of the other sites investigated in MUSTANG project is also included, namely work from the sites Hontomin, Maguelone and a natural analog site in the North Sea. The results are intended to add to our understanding on relevant properties of geological formations as candidates for CO2 geological storage.
ISSN: 1750-5836

hal-01356326
https://hal.archives-ouvertes.fr/hal-01356326
DOI : 10.1016/j.ijggc.2016.02.007

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
In this paper we solve the Navier Stokes’ equation using finite difference method, on a simulated porous rock structure in 2-D, to study the velocity distribution of fluid flowing through it under a constant pressure gradient. A reactive solute carried through the fluid is allowed to interact with the minerals in the rock. Depending on the rock composition, both dissolution and precipitation reactions may occur. However precipitation occurs only through the cations that are released in the solution due to dissolution. These combined dissolution–precipitation reactions change the porosity, permeability and pore geometry of the sedimentary rock. We study the temporal changes of these properties as functions of Peclet number, concentration of the reactive solute and ratio of Damkholer numbers of dissolution to precipitation. The final flow property is decided by a combination of these parameters.
ISSN: 0022-1694

hal-01115291
https://hal.archives-ouvertes.fr/hal-01115291
DOI : 10.1016/j.jhydrol.2014.10.019

Éditeur(s) : HAL CCSD Elsevier
Résumé : We investigate experimentally the alteration of fractured class-G cement flowed by CO2-rich brine. The experiment mimics a mechanically damaged rough-walled fractured cement annulus at temperature 60 °C and pressure 10 MPa. The experiment consists of flowing a reservoir-equilibrated brine mixed with CO2 (partial pressure of 2.3 MPa) through the fracture of average aperture 14 μm at constant flow rate (100 μL min−1). This flow rate corresponds to pressure gradient representative of an average in situ hydrodynamic condition. Results indicate an intense alteration of the cement with a large removal of mass at the scale of the sample. However, the fracture alteration patterns are triggered by the initial heterogeneity of the fracture aperture; the aperture of the low aperture zones tends to decrease due to calcite precipitation whereas preferential paths develop in the zones of higher aperture associated. Nevertheless, the expected large permeability increase triggered by the mass removal is mitigated by the precipitation of a low density Si-rich amorphous material. The alteration rate will decrease with time because of the increasing distance of diffusion between the fracture where the reactants are actively renewed by advection and the portlandite and C-S-H dissolution fronts. The different zones of reaction can be adequately modeled by a simple 1D diffusion-reaction model using published kinetics coefficients and extrapolation to larger times than the experiment time can be drawn. Altogether, and in addition to the previous studies of the alteration of fractured well cement annulus, this study shows that the leakage potential is strongly controlled by the initial distribution of the aperture along the fracture: low aperture zones will tend to self-heal while localized flow in connected high aperture paths will be perennial.
ISSN: 1750-5836

hal-01346006
https://hal.archives-ouvertes.fr/hal-01346006
DOI : 10.1016/j.ijggc.2016.01.032

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
An analytical solution in the Laplace domain is derived for modeling anomalous pressure diffusion during pumping tests in aquifer displaying hierarchical fractal fracture networks. The proposed solution generalizes all of the analytical models for fractal flow published previously by combining multifractal diffusion and nested multiporosity with transient exchanges, interface skin effects, and well storage effect. Solutions are derived for fracture-delimited blocks with planar, cylindrical, and spherical shapes, as well as with any fractional dimensional shapes. Any combinations of these shapes can be defined in order to model a large range of situations. Within each permeability level, the fractal properties of the fracture network can be specified and the fractal dimension can be distinct from the shape dimension of the block.
ISSN: 0043-1397

hal-00411549
https://hal.archives-ouvertes.fr/hal-00411549
DOI : 10.1029/2008WR007125

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Carbonation of peridotite is a widespread process in nature, with emerging societal and environmental implications through geological storage of CO2. We studied the micro- and nano-scale structures associated with the carbonation of peridotite pervaded by a CO2-rich water and the induced changes of its hydrodynamic properties. Focused ion beam (FIB) nanotomography was coupled with scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. An experimental sample of dunite core percolated by a CO2-rich fluid (pCO2 = 11 MPa) at 160 °C was compared with a naturally carbonated sample from the Atlantic Ridge (Exp. IODP 304). Results of the 8-days percolation experiment show continuous alteration of olivine into magnesite locally associated with a poorly crystalline serpentine-type mineral referred to as proto-serpentine. The experiment is also characterized by an overall decrease in rock porosity (from 7.7 to 6.4%) and permeability (from 8.5 × 10− 16 to 1.7 × 10− 16 m2). The primary inter-granular porosity (1 to 10 μm) is progressively filled with magnesite, leading to the overall decrease of permeability. At the same time, a secondary small-scale porosity (10 nm to 1 μm) is created at the tip of the dissolution features along the (010) cleavage planes of olivine grains. Carbonate crystals grow within these etch-pit structures behind the dissolution front. Dissolution and precipitation occur at a relative rate that maintains the secondary porosity over the timescale of the experiment (i.e. carbonate growth has to be the slowest one). This process is interpreted as an interface coupled dissolution-precipitation mechanism of olivine carbonation. Proto-serpentine is only formed in highly reduced flow areas, such as small olivine etch-pits (10 to 500 nm wide), which are more isolated from CO2 input. SEM-FIB analyses show the 3D preferential orientation of the dissolution-precipitation planes within a given olivine grain. It suggests the formation of lateral connections between the etch-pits (infra-micrometric “channels”) providing access to reactants and removing reaction products at the reaction sites. The experimental results show that olivine dissolution and magnesite precipitation converge to a quasi-steady state resulting in a constant carbonation rate controlled by reaction kinetics and not by mass transfer for this flow regime. The system self-regulates, independently of the porosity change at least during this incipient stage of olivine carbonation. Similar textures are observed in natural samples collected at 170 m-depth in the vicinity of veinlets driving late fluids down into the cooling oceanic lithosphere. This suggests that similar mechanisms are active in nature and can play an important role in the late, low temperature alteration stages of fractured peridotite. These results also highlight the critical role of nm-scale spatial arrangement of dissolution and precipitation features on mass transfers and on the sustainability of olivine carbonation through coupled dissolution-precipitation processes.
ISSN: 0009-2541

hal-01684733
https://hal.archives-ouvertes.fr/hal-01684733
DOI : 10.1016/j.chemgeo.2017.11.013

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
The main goal of the monitoring stage of Carbon Capture and Storage (CCS) is to obtain an accurate estimation of the subsurface CO2 accumulation and to detect any possible leakage. Laboratory experiments are necessary to investigate the small scale processes governing the CO2–brine–rock interaction. They also provide a means to calibrate the results coming from field scale geophysical methods. In this work we set up an experimental system which is able to perform Electrical Resistivity Tomography (ERT) measurements on centimeter-scale rock samples at various P–T conditions. We present the results of two new experiments related to CO2 monitoring, performed on a cylindrical (4 × 8 cm) Fontainebleau rock sample. In the first one, we have quantified the CO2 saturation at different volume fractions, representing zones from a deep saline aquifer with varying degrees of saturation. In the second one, we have monitored and quantified the effect of CO2 dissolution in the brine at a pressure of 40 bar during eight days, emulating the invasion of CO2 into a shallow aquifer. Results highlight the importance of accounting for the contribution of surface conductivity in highly CO2-saturated regions, even in clay-free rocks, and also for brine conductivity variation due to CO2 dissolution. Ignoring any of these effects will end up in a CO2 saturation underestimation. We present a modified CO2 saturation equation to account for these two influences.
ISSN: 0926-9851

hal-01356323
https://hal.archives-ouvertes.fr/hal-01356323
DOI : 10.1016/j.jappgeo.2016.03.039

Éditeur(s) : HAL CCSD
Résumé : In order to minimize CO2 atmospheric concentration, a solution consists in sequestrating CO2 in geological reservoirs. To estimate long term risks, it is necessary to quantify the couplings between reaction processes as well as structural and hydrodynamical modifications. We realised two experimental benches enabling injecting CO2-enriched-brine in conditions corresponding to in situ storage (T < 200 oC and P < 200 bar) and developed
an experimental protocol using X-Ray microtomography and fluid and rock analyses in order to measure the variations of physical and chemical parameters.
The study of carbonated reservoirs near the injection well, allows quantifying different k-phi relationships depending on the dissolution processes and triggered by the local fluid chemical composition and initials conditions. Away from the injection well, we observe carbonate precipitation decreasing the permeability. The study of fracturated caprock samples shows that alternative percolation of CO2-enriched-brine and CO2 gas increases the fracture permeability.
The study of silicated rocks indicates carbonate precipitation in zeolite sandstone and sintered dunite grains. Nevertheless, in zeolite sandstone we also observe the precipitation of clay particles located in the uid pathways which decrease strongly the permeability.
Afin de minimiser la concentration en CO2 dans l'atmosphère une solution consiste à le séquestrer dans les réservoirs géologiques. Pour évaluer les risques à long terme, il est nécessaire de quantifier les couplages entre les processus réactionnels et les modifications structurales et hydrodynamiques. Dans cette optique, nous avons construit deux dispositifs expérimentaux permettant d'injecter des saumures chargées en CO2 dans les conditions de stockage (T < 200 °C et P < 200 bar) et mis en oeuvre un protocole expérimental utilisant la microtomographie RX et l'analyse des roches et des fuides pour quantifier les variations des paramètres physiques et chimiques. Dans le cas des réservoirs carbonatés, on observe, près du puits d'injection, une forte variabilité des relations k-phi en fonction du régime de dissolution contrôlé par la chimie locale du fluide, ainsi que par les conditions initiales. A plus grande distance, on observe des processus de précipitation diminuant fortement la perméabilité. L'étude des roches de couverture fracturées (argilite) a montré qu'une percolation alternée d'une saumure chargée en CO2 et de CO2 gaz augmentait la perméabilité de fracture. Dans le cas des roches silicatées, la précipitation de carbonates est mise en évidence aussi bien dans les grès à zéolites que dans les frittés de dunite de San Carlos. Cependant, dans les grès à zéolites, la précipitation d'une phase argileuse est observée dans les chemins d'écoulement et engendre une forte diminution de la perméabilité.
https://tel.archives-ouvertes.fr/tel-00416408

tel-00416408
https://tel.archives-ouvertes.fr/tel-00416408
https://tel.archives-ouvertes.fr/tel-00416408/document
https://tel.archives-ouvertes.fr/tel-00416408/file/These_Luquot.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
Résumé : International audience
RST 2008
Nancy, France

hal-00569242
https://hal-mines-paristech.archives-ouvertes.fr/hal-00569242

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Numerical programs for simulating flow and reactive transport in porous media are essential tools for predicting reservoir properties changes triggered by CO2 underground injection. At reservoir scale, meshed models in which equations are solved assuming that constant macroscopic properties can be defined in each cells, are widely used. However, the parameterization of the dissolution-precipitation problem and of the feedback effects of these processes on the flow field is still challenging. The problem arises from the mismatch between the scales at which averaged parameters are defined in the meshed model and the scale at which chemical reactions occur and modify the pore network geometry. In this paper we investigate the links between the dissolution mechanisms that control the porosity changes and the related changes of the reactive surface area and of the permeability. First, the reactive surface area is computed from X-ray microtomography data obtained before and after a set of dissolution experiments of pure calcite rock samples using distinctly different brine-CO2 mixtures characterizing homogeneous to heterogeneous dissolution regimes. The results are used to validate the power law empirical model relating the reactive surface area to porosity proposed by Luquot and Gauze (2009). Second, we investigate the spatial distribution of the effective hydraulic radius and of the tortuosity, two structural parameters that control permeability, in order to explain the different porosity-permeability relationships observed for heterogeneous and homogeneous dissolution regimes. It is shown that the increase of permeability is due to the decrease of the tortuosity for homogeneous dissolution, whereas it is due to the combination of tortuosity decrease and hydraulic radius increase for heterogeneous dissolution. For the intermediate dissolution regime, identified to be the optimal regime for increasing permeability with small changes in porosity, the increase of permeability results from a large increase in the mean effective hydraulic radius of the sample.
ISSN: 0169-7722

hal-00617671
https://hal.archives-ouvertes.fr/hal-00617671
DOI : 10.1016/j.jconhyd.2010.07.004