Éditeur(s) : HAL CCSD Oxford University Press (OUP)
Résumé : International audience
Previous work has demonstrated that geoelectrical measurements, acquired either along the Earth’s surface or in boreholes, can be sensitive to the presence of fractures. However, a lack of numerical approaches that are well suited to modelling electric current flow in fractured media prevents us from systematically exploring the links between geoelectrical measurements and fractured rock properties. To address this issue, we present a highly computationally efficient methodology for the numerical simulation of geoelectrical data in 2.5-D in complex fractured domains. Our approach is based upon a discrete-dual-porosity formulation, whereby the fractures and rock matrix are treated separately and coupled through the exchange of electric current between them. We first validate our methodology against standard analytical and finite-element solutions. Subsequent use of the approach to simulate geoelectrical data for a variety of different fracture configurations demonstrates the sensitivity of these data to important parameters such as the fracture density, depth, and orientation.
ISSN: 0956-540X

hal-01622151
https://hal.archives-ouvertes.fr/hal-01622151
https://hal.archives-ouvertes.fr/hal-01622151/document
https://hal.archives-ouvertes.fr/hal-01622151/file/sanzGJI2017.pdf
DOI : 10.1093/gji/ggx080

Éditeur(s) : HAL CCSD American Geophysical Union
Résumé : International audience
The Iberian Massif is the best exposed segment of the European Variscan Belt. It includes relatively well preserved terranes that were accreted by transpression along time and resulted in a number of geotectonic units that formed part of the Late Paleozoic assembly of the Pangaea Supercontinent. In SW Iberia, these units are the Central Iberian Zone (CIZ), Ossa Morena Zone (OMZ), and the South Portuguese Zone (SPZ). A 210 km long NE-SW magnetotelluric profile was carried out through the CIZ, from the OMZ-CIZ boundary toward the north, reaching the Tagus (Cenozoic) basin. Data dimensionality analysis resulted in a suitable 2-D electrical resistivity structure, allowing a 2-D inversion of the data set. Complementary available geophysical data (deep seismic, gravity and aeromagnetic) and a comparison with a detailed geological cross section led us to constrain the interpretation of the 2-D electrical resistivity structure of the CIZ crust. The results show, for the upper crust, the existence of diverse conductive/resistive bodies that correlate well with known geological features (sedimentary basins, faults, granitic plutons, mineralized systems). A mild but steady conductive band is located along the middle and lower crust that is interpreted as a mafic granulite basement. The upper section of this band connects with several elongated shallow conductors, providing further evidence for the existence, in the Central Iberian Zone, of a complex decollement system where the major faults are rooted. Such a crustal architecture is viewed as the northward continuation of the Variscan large-scale structures previously recognized in the southern sectors (OMZ and SPZ).
ISSN: 0148-0227

hal-00671036
https://hal.archives-ouvertes.fr/hal-00671036
DOI : 10.1029/2010JB007538

Éditeur(s) : HAL CCSD Springer Verlag
Résumé : International audience
Electrical resistivity soundings are used by geophysicists to determine the structure and composition of the Earth's crust and mantle and to explore natural resources (ore, oil, gas, water). Their interpretations in terms of composition and in-situ physical conditions depend mainly on laboratory measurements of electrical conductivity of rocks at simulated crustal conditions of temperature, pressure, saturation and pore pressures. These measurements present a numbers of limitations, in particular, in the case where conductive pore fluids are present, as in the case of deep reservoir conditions, where temperature exceeds 250 A degrees C. Here, we present a new cell capable of measuring electrical conductivity of large saturated samples at confining pressure up to 200 MPa, pore pressure up to 50 MPa, and temperature up to 500 A degrees C. The measurement cell has been developed in a commercial, internally heated, gas pressure apparatus (Paterson press). It is based on the concept of "guard ring" electrode, which is adapted to samples that are jacketed by a very conductive, metallic material. Numerical modeling of the current flow in the electrical cell allowed defining the optimal cell geometry. Calibration tests have been performed on Fontainebleau sandstones saturated with electrolytes of different conductivities, up to 350 A degrees C. The resulting electrical formation factor and temperature dependence of electrical conductivity are in very good agreement with previous studies. This new cell will improve the exploration and exploitation of deep fluid reservoirs, as in unconventional, high enthalpy geothermal fields. In particular, the investigations address possible effects of fluid-rock interactions on electrical resistivity of a reservoir host rock.
ISSN: 0169-3913

hal-00681997
https://hal.archives-ouvertes.fr/hal-00681997
DOI : 10.1007/s11242-011-9846-2

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
A shallow field experimental site for CO2 injection was established at Maguelone (Languedoc, France), in order to test in an integrated manner a suite of surface and downhole hydrogeophysical monitoring methods. The objective is to improve monitoring of gas transport in the shallow subsurface and to determine the sensitivity of CO2 monitoring systems for leakage detection. The site offers a natural laboratory to study the processes associated with CO2 injection in a clastic and clay-rich context saturated with saline fluids. Prior to CO2 injection, three nitrogen (N2) injections were undertaken in 2012 to measure the site response to neutral gas injection. In 2013, a volume of 111 m3 (mass of 220 kg) of CO2 was injected during 3.5 h at 15 m depth. During each experiment, the gas plumes were successfully detected from pressure monitoring, time-lapse induction logging and downhole resistivity monitoring with dipole–dipole array. Increases in resistivity are attributed to free gas propagation (either N2 or CO2) whereas decreases in resistivity correlate with CO2 dissolution in the pore fluid. Chemical analyses confirm this hypothesis with a decrease in pH and an increase in the concentration of dissolved species in the latter case.
ISSN: 1750-5836

hal-01355943
https://hal.archives-ouvertes.fr/hal-01355943
DOI : 10.1016/j.ijggc.2015.12.005

Éditeur(s) : HAL CCSD
Résumé : International audience
Understand the dynamics of the fresh-salt water interface in aquifers is a key issue to comprehend mixing processand to quantity the discharge of nutrients in to coastal areas. In order to go beyond the current knowledge inthis issue an experimental site has been set up at the alluvial aquifer Riera Argentona (Barcelona – Spain). Thesite comprises 16 shallow piezometers installed between 30 and 90 m from the seashore, with depths rangingbetween 15 and 25 meters. The seawater interface is being monitored using several techniques, the combinationof which will help us to understand the spatial and temporal behaviour of the mixing zone and the geochemicalprocesses occurring there. Specially the deepest piezometers are equipped with electrodes in order to performcross-hole electrical resistivity tomography (CHERT). In addition, all piezometers are also equipped with FiberOptic cable to perform distributed temperature measurements. Two single steel armoured fibre optic cable lines ofaround 600m length were installed in all boreholes. The objective is to use the cable both as passive and activetemperature sensor. The first is being done for the continuous monitoring of temperature whereas; the secondprovides a higher temperature resolution used to monitor field experiments.Periodic CHERT measurements are carried out between the piezometer equipped with electrodes, resultingin parallel and perpendicular vertical cross sections of the site resistivity. The position of the fresh-salt waterinterface can be identified due to the resistivity contrast between the saline and fresh water. Preliminary resultsof periodic distributed temperature measurements will be also be used to monitor the position of the mixing zonethanks to the contrast and seasonal temperature changes. Periodic down-hole EC profiles will be used to validatethe method.AcknowledgementsThis work was funded by the projects CGL2013-48869-C2-1 y CGL2013-48869-C2-2-R of the Spanish Government.We would like to thank SIMMAR (Serveis Integrals de Manteniment del Maresme) and the ConsellComarcal del Maresme in the construction of the research site
European Geosciences Union General Assembly 2016
Vienne, Austria

insu-01308757
https://hal-insu.archives-ouvertes.fr/insu-01308757

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
To evaluate the performance of downhole and surface geophysical monitoring methods, a series of shallow gas injection-monitoring experiments has been performed in a coastal saline aquifer at Maguelone, France. The recorded data include pressure measurements with a Westbay multilevel completion and CO2 saturation at an observation well derived from electrical resistivity with a modified Waxman-Smits (MWS) model. In this work, the aim is to develop a simulation model capturing the gas transport behavior and consistent with field data. For this purpose, the simulation of the CO2 injection experiment is carried out with two conceptual models, a homogeneous model and a heterogeneous model treated with multiple realization Monte Carlo simulations. Numerical simulator TOUGH2 with the equation of state module EOS7C is used for the simulations. Comparison of the model results with field data suggests that the pressure responses are captured with relatively good accuracy. Similarly, the model also provides an overall reasonable agreement and correct order of magnitude for predicted gas saturation values. However, as the heterogeneity pattern in the field data remains largely unknown, the model predictions can only be used to capture the mean behavior as well as to provide insights into how heterogeneity can influence the system behavior, by means of sensitivity analyses of the influence of heterogeneities on individual realizations.
ISSN: 1750-5836

hal-01467240
https://hal.archives-ouvertes.fr/hal-01467240
DOI : 10.1016/j.ijggc.2016.09.006

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

Résumé : Les aciers inoxydables à haute teneur en molybdène présentent une excellente résistance à la corrosion et ont été récemment utilisés dans des applications marines. L'acier inoxydable de type 254 SMO contient du molybdène (6% Mo) et des quantités plus élevées en éléments d'alliages que les aciers inoxydables plus classiques tels que 304, 316 et 316L. Alors que Anees Uddin Malik et al. montrent que l’acier 254 SMO est moins sensible à la corrosion par piqûre en eau de mer du golfe persique, Abdulsalam et al. démontrent que bien que cet acier présente une bonne résistance à la corrosion, il reste encore sensible à une corrosion caverneuse (surtout en milieu à 16% en masse d’ion chlorure ou à plus de 30°C).La première partie de ce travail traite du comportement électrochimique de l’acier inoxydable 254 SMO immergé dans l’eau de mer naturelle en laboratoire. Ainsi deux sites de la Guyane ont été choisis pour effectuer des prélèvements d’eau. Des analyses physicochimiques de ces eaux sont réalisées et montrent que l’eau du site du Port Larivot contient une quantité en ions chlorures plus importante que celle de l’eau du site du Mahury. Une colonisation par des bactéries et crustacés (balanes) a été mise en évidence, à l’aide du microscope électronique à balayage environnemental. Les mesures électrochimiques, notamment la voltammétrie cyclique a montré l’existence d’une zone de passivation et l’augmentation du courant de passivation par un facteur de 10 en présence d’un biofilm pour l’acier inoxydable immergé en eau du Mahury durant 22 jours. La deuxième partie propose une étude approfondie du comportement de l’interface complexe métal/couche passive/biofilm. Trois différents coupons d’aciers inoxydables (brut, poli et grenaillé) ont été déposés sur site (in-situ) dans un premier temps. Dans une seconde étape, nous avons réalisé des expérimentations mixtes (incubation in-situ et croissance en laboratoire). L’évolution du potentiel d’abandon de ces aciers est très proche pour l’acier brut et l’acier poli. En revanche, celui de l’acier grenaillé, de par la présence des grains d’alumine à sa surface, affiche un comportement différent. Une étude comparative des deux expérimentations montre des différences concernant les paramètres électriques de l’interface complexe métal/couche passive/biofilm.
Stainless steels with high content in molybdenum present an excellent corrosion resistance and were recently used in marine applications. The stainless steel 254 SMO contains molybdenum (6 %) and higher amounts of alloying elements than conventional stainless steels such as 304, 316 and 316L. While Anees Uddin Malik et al. show that 254 SMO steel is less likely to be susceptible to pitting corrosion in Arabian Gulf sea water, Abdulsalam et al. demonstrate that although this steel has good resistance to corrosion, it remains still susceptible to crevice corrosion (especially in environment with 16 chloride percent weight or more than 30 ° C).The first part of this work deals with the electrochemical behaviour of stainless steel 254 SMO immersed in natural seawater at laboratory. Two sites in French Guyane were chosen to take samples of seawater. Physicochemical analyses of these waters are made and show than the in Port Larivot site seawater contains a higher quantity of chloride ion than to Mahury seawater. Colonization by bacteria and crustaceans (barnacles) was highlighted, using the environmental scanning electron microscope. The electrochemical measurements, including cyclic voltammetry showed the existence of a passivation region and increasing the passivation current by a factor of 10 in the presence of biofilm on stainless steel immersed in Mahury seawater during 22 days.The second part offers a detailed study of the behaviour of the interface metal/passive film/biofilm. Three different coupons of stainless steel (crude, polished and blasted) were deposited on the site (in-situ) in the first time. In a second step, we performed experiments mixed (in-situ incubation and growth in the laboratory). The evolution of the free potential of these steels is very close for crude steel and polished steel. Conversely, the blasted steel, by the presence of alumina grains on its surface, shows a different behaviour. A comparative study of those two experiments shows differences in the electrical parameters of the interface metal/passive film/biofilm.

http://www.theses.fr/2013AGUY0598/document

Éditeur(s) : HAL CCSD
Résumé : This thesis has been conducted on a fractured crystalline basement located in Ploemeur (South of Brittany, France). The detailed study of this basement requires a good understanding of their internal structures, namely their intrinsic properties, flow mode, density and fractures distribution. This work is focused on the petrophysical characterization of the granitic formations. Physical properties were determined from downhole geophysical measurements and images, and petrophysical measurements with thin sections made for each mini-core in the laboratory. Fresh-altered schist and fresh-altered granite separated by a normal angle fault are the main lithology of the Ploemeur crystalline basement. The results showed that the petrophysical properties were function of both porosity variation and degree of alteration and that the pore-space topology was found to be porositydependent. This thesis introduces a new formula between electrical resistivity and porosity. In addition, the laboratory measurements of Ploemeur revealed that seismic wave velocity was a function not only of porosity, but also of the predominant pore type. In general, the pore aspect ratio inverted from velocity measurements were classified roughly into crack shape. In the Ploemeur crystalline basement, the downhole geophysical measurements and images were used to measure changes in physical and chemical properties in the borehole fluid and the bedrock surrounding the boreholes. The effective integration of different geophysical methods, hydrogeological tests and lithological description was the best way to characterize the fractures in the crystalline basement, and is critical for a suitable estimation of fluid circulation.
Le socle cristallin fracturé, situé à Ploemeur (Bretagne sud, France) est l'objet de ce travail de thèse. L'étude détaillée du socle nécessite une bonne compréhension de la structure interne, à savoir les propriétés intrinsèques, le mode d'écoulement, la densité et la distribution des fractures. Ce travail de thèse est consacré à la caractérisation pétrophysique des formations granitiques. Les propriétés physiques ont été déterminées à partir de l'interprétation des données de mesures de géophysique en forage, des images de paroi du puits et des mesures pétrophysiques réalisées sur carottes en laboratoire. Afin de replacer les mesures dans leur contexte lithologique, une lame mince a été analysée pour chaque mini-carotte. Les formations lithologiques rencontrées dans le socle cristallin de Ploemeur sont des schistes et granites sains et altérés, ces deux lithologies étant séparées par une zone de faille. Les résultats ont montré que les propriétés pétrophysiques des roches étaient fonction à la fois de la variation de la porosité et du degré d'altération des roches et que la topologie de l'espace poreux était fortement dépendante de la porosité. Cette thèse introduit une nouvelle formule entre la résistivité électrique et la porosité. De plus, les mesures en laboratoire sur les échantillons de Ploemeur révèlent que les vitesses sismiques ne sont pas seulement fonction de la quantité de porosité, mais aussi fonction de facteur de forme. Ce dernier a été calculé sur les échantillons du socle de Ploemeur à partir des vitesses acoustiques. Les résultats ont montré que la porosité est de forme fissurale. L'intégration des données issues des images optiques et acoustiques, des mesures de géophysique en forage, et de la description des carottes a permis d'étudier de façon détaillée la géologie et l'hydrodynamique du socle de Ploemeur. L'intégration effective de ces différentes méthodes avec les tests hydrogéologiques ressort comme la meilleure façon de caractériser les fractures et les circulations en eau dans le socle.
https://tel.archives-ouvertes.fr/tel-00444175

Droits : info:eu-repo/semantics/OpenAccess
tel-00444175
https://tel.archives-ouvertes.fr/tel-00444175
https://tel.archives-ouvertes.fr/tel-00444175/document
https://tel.archives-ouvertes.fr/tel-00444175/file/thesebelghoul.pdf

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
An original karstic system in a coastal alluvial plain located in a carbonate environment (Cassis, Provence -- SE France) was studied using a multi-method approach (electrical resistivity tomography, gravimetric, passive seismic survey), combined with geomorphologic methods, surface observations and drilling. Limestone dissolution and/or cavity collapse led to the development of a polje, which was filled rapidly by erosion of Aptian marls. The combination of several dating and paleoenvironmental proxies indicates that the polje was filled during a glacial period (MIS 6, 8 or 10, i.e. in the 130-360 ka age range). This discovery has implications for the understanding of karst processes. The connection between the polje and the three km-long Bestouan underwater karstic conduit with submarine outlet is strongly suggested by sedimentological studies and geophysical prospections.
ISSN: 0169-555X

hal-01054334
https://hal.archives-ouvertes.fr/hal-01054334
DOI : 10.1016/j.geomorph.2014.02.021

Éditeur(s) : HAL CCSD Elsevier
Résumé : Adequate hydrogeophysical monitoring of CO2 geological storage remains a challenge as different parameters might be modified during storage. That implies to compare real-time measurements to an adequate baseline. At the Maguelone shallow experimental site a representative baseline for electrical resistivity was built from a large number of downhole geophysical measurements. At this coastal site this issue is particularly important due to the production of biogenic gas from the subsurface sediments. For this, a modified petrophysical model based on the Waxman-Smits model is proposed to estimate gas saturation found to vary from 2 to 7% within shallow sand layers.
ISSN: 1876-6102

hal-01412685
https://hal.archives-ouvertes.fr/hal-01412685
https://hal.archives-ouvertes.fr/hal-01412685/document
https://hal.archives-ouvertes.fr/hal-01412685/file/pezard2015.pdf
DOI : 10.1016/j.egypro.2015.07.910

Éditeur(s) : HAL CCSD Elsevier
Résumé : International audience
Active faults from the Campo de Dalías (SE Betic Cordillera) allow us to constrain the deformation styles involved in the development of segmented oblique-slip faults. This sector constitutes the widest outcrop of Plio-Quaternary sediments in the northern boundary of the Alboran Sea. It has emerged since the Late Pliocene, and therefore provides recent deformation markers that are not disturbed by erosive processes. The faults started to grow during the Pleistocene, reactivating previous hybrid joints, with a normal-dextral slip. We present a detailed map of the largest fault in the area, the Loma del Viento fault, comprising six onshore segments. Based on field work and aerial photography, the distributions of the contiguous joints have been mapped, and the joints reactivated as faults are identified. Some of these fault segments are hard-linked, and fault slip enhances toward the linkage sectors between them with associated sedimentary depocenters. An electrical tomography profile reveals the wedge geometry of a unit of Pleistocene conglomerates and red silts that were coevally deposited during the fault movement. Long-term slip rate in the central part of the fault is estimated at 0.07 ± 0.03 mm/y. In addition, a seismic crisis nucleated close to the Loma del Viento fault during November 2010 was recorded. Moment tensor analysis of the two mainshocks (Mw 3.5 and 4.2) provides a focal solution indicating a N120°E striking right-lateral strike-slip fault. The corrugated morphology of the Loma del Viento fault may have influenced its seismic behavior. Some of the fault segments are oblique to the general motion of the fault. These oblique segments would provide higher resistance against the general fault motion and could lock the fault, leading to accumulate elastic energy.
ISSN: 0040-1951

hal-00750357
https://hal.archives-ouvertes.fr/hal-00750357
DOI : 10.1016/j.tecto.2011.12.001