[pt] A grande maioria dos problemas de estabilidade de poços de petróleo ocorre em trechos de folhelhos, rochas nas quais, uma especificação eficiente da pressão do fluido de perfuração requer previamente uma especificação correta da concentração salina e da temperatura. Todavia, para um dimensionamento adequado das características do fluido de perfuração necessárias à estabilidade do poço, é necessário o uso de modelos matemáticos que considerem um acoplamento adequado entre efeitos poroelásticos, químicos e térmicos. Entretanto, a complexidade matemática das equações de modelos acoplados normalmente leva à adoção de soluções numéricas, que consomem um tempo computacional muito grande e, por isso, esses modelos não são atrativos à aplicação na análise da estabilidade de poços. Este trabalho apresenta um modelo acoplado termo-químico-poroelástico representado por duas soluções, uma numérica, que utiliza o método dos elementos finitos, e outra analítica, baseada no método das transformadas de Laplace. Ao comparar ambas as soluções é demonstrado que a solução analítica consegue representar tão bem quanto à solução numérica os principais processos acoplados presentes durante a perfuração de folhelhos e que influenciam na sua estabilidade e, por esta razão, pode ser utilizada na análise de estabilidade de poços em folhelhos. Através de um estudo de caso, é verificado que um controle eficiente da estabilidade do poço é obtido especificando a pressão do fluido de perfuração em função da sua temperatura e concentração salina. Estes resultados também indicam as razões de alguns problemas não previstos por modelos desacoplados, e que quase sempre ocorrem durante a perfuração em folhelhos. / [en] Wellbore stability problems are most common when drilling through shales. In order to avoid such problems in this kind of rocks the solute concentration and temperature must be properly defined in the drilling fluid composition, which requires considering poroelastic, thermal and chemical effects in a coupled way. The equations complexity of coupled models usually results in numerical solutions that are very time consuming, thus, unattractive for stability analysis. In an opposite way, it is very difficult to develop closed- form solutions for coupled models. This work presents a thermochemoporoelastic model represented by a numerical solution based upon the finite element method and an analytical solution based upon the Laplace transform method. A comparison between the results of the numerical solution and analytical solution shows that the later can reproduce the coupled processes involved in the wellbore stability problem in shales as well as the former, and for this reason the closed-form solution can be applied as a practical tool in wellbore stability analysis. The analysis of a typical wellbore drilled through shales showed that an efficient control of wellbore stability can be obtained through an adequate specification of the drilling fluid pressure when taking in account its solute concentration and temperature. The model was also able to explain some problems not predicted by uncoupled models, but almost always seen while drilling through shales.

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Le Pb est omniprésent dans les échantillons terrestres et sa relation avec ses ascendants radioactifs, l’U et le Th, en fait un marqueur de choix des processus géodynamiques.L’équipe lyonnaise de Janne Blichert-Toft et Francis Albarède a démontré, à travers une vaste compilation de données bibliographiques accompagnée de la production de nouvelles mesures, une correspondance entre la répartition des valeurs de composition isotopique du Pb dans la croûte continentale et la localisation de figures tectoniques majeures sur plusieurs continents (Bouchet et al., 2014 ; Blichert-Toft et al., 2016 ; Delile et al., 2014). L’existence de ces "provinces géochimiques" démontre l’intérêt des isotopes du Pb comme outil pour mieux comprendre comment l’histoire tectonique d’une région façonne la géochimie de ses continents. Un premier volet de ces travaux de thèse visait à compléter la base de données existante des compositions isotopiques du Pb dans la croûte continentale européenne, grâce à l’analyse de 104 échantillons de feldspaths potassiques issus de granites principalement originaires de Catalogne, de Corse, de Galice et de Kabylie, jusqu’ici restées en blanc sur les cartes précédemment établies. Les cartes ainsi obtenues, illustrant la répartition à travers l’Europe et le bassin méditerranéen des valeurs des "paramètres géochimiques" définis par Albarède et al. (2012), exprimant à partir des rapports isotopiques du Pb mesurés l’âge modèle de la roche et les fractionnements entre l’U, le Th et le Pb enregistrés en son sein, confirment le potentiel des isotopes du Pb comme traceurs robustes de l’héritage tectonique d’une région.Mais le cœur de cette thèse a été d’appliquer cet outil reliant chimie et histoire géodynamique que sont les isotopes du Pb à un type d’échantillon géologique pour lequel des analyses de haute précision de la compositions isotopique en Pb n’avaient jamais été entreprises jusqu’à maintenant : les pétroles bruts. Pour cela, il a fallu développer une méthode analytique novatrice permettant d’extraire le Pb de quelques millilitres de pétrole brut vers une solution aqueuse adaptée aux protocoles habituels de purification indispensables à des analyses isotopiques du Pb à haute précision par MC-ICP-MS (Fetter et al., 2019). Cette méthode a ensuite été appliquée à un total de 211 échantillons de pétrole brut issus de partout dans le monde. Des échantillons de roches mères d’hydrocarbures (schistes noirs) ont également été analysés afin de compléter les premières interprétations des résultats. Ce jeu de données unique met en évidence que le Pb contenu dans les pétroles bruts résultait du mélange d’au moins trois composantes d’âges modèles distincts : le pôle le plus radiogénique a été identifié comme associé aux roches mères des pétroles, tandis que les deux autres, d’âges modèles paléozoïque et protérozoïque, suggèrent des interactions conséquentes entre le pétrole et les roches encaissantes et sous-jacentes. Un nouveau modèle de migration du pétrole depuis sa roche mère a donc été proposé (Fetter et al., soumis), prenant en compte la forte implication des eaux circulant en profondeur dans les bassins sédimentaires en faisant intervenir un phénomène grandement négligé jusqu’à maintenant : la solubilité mutuelle de l’eau et du pétrole à haute température.La mise en évidence d’une dynamique complexe du Pb dans les pétroles bruts invalide une utilisation de ces derniers comme alternative aux feldspaths potassiques pour obtenir des données isotopiques en Pb fiables sur la croûte continentale européenne située sous les bassins sédimentaires. Cependant, elle ouvre de nouvelles portes quant à l’utilisation jusqu’ici inexplorée des isotopes du Pb comme traceurs de phénomènes de pollution associés à une prospection pétrolière peu responsable. / Lead is ubiquitous in terrestrial samples and its relationship to its radioactive ascendants, U and Th, makes it a prime tracer of geodynamic processes.The team of Janne Blichert-Toft and Francis Albarède, based in Lyon (France), has demonstrated on several continents, through large compilations of literature data supplemented by new measurements, a correspondence between the distribution of Pb isotopic compositions in the continental crust and major tectonic features (Bouchet et al., 2014 ; Blichert-Toft et al., 2016 ; Delile et al., 2014). The existence of these "geochemical provinces" has firmly established the potential of Pb isotopes as a tool for understanding how the tectonic history of a given region shaped its geochemistry. A first aspect of this PhD aimed at complementing the existing database of Pb isotopic compositions of the European continental crust through the analysis of 104 K-feldspar samples separated from granites originating mainly from Catalonia, Corsica, Galicia, and Kabylie, up until this PhD blank areas on the compiled map. The resulting updated maps showing the distribution throughout Europe and the circum-Mediterranean area of the "geochemical parameters" defined by Albarède et al. (2012), which derive a model age and fractionations between U, Th, and Pb from measured Pb isotopic ratios, confirm the potential of Pb isotopes as powerful tracers of the tectonic heritage of a given region.The core of this PhD, however, was to apply this tool connecting chemistry and geodynamic history to a type of geological sample so far never analyzed for high-precision Pb isotopic compositions: crude oil. To achieve this goal, a novel analytical method was developed which allows the extraction of Pb from a few milliliters of crude oil into an aqueous solution suitable for the standard Pb purification protocol essential for high-precision Pb isotope analysis by MC-ICPMS (Fetter et al., 2019). This method was then applied to a total of 211 crude oil samples from around the world. Hydrocarbon source rocks (black shales) also were analyzed. This unique data set reveals that Pb in crude oil results from the mixing of at least three endmembers of distinct model ages: the more radiogenic endmember is identified as the oil source rocks, while the other two components, of Paleozoic and Proterozoic ages, suggest considerable interactions between crude oil and the surrounding and underlying rocks. A new model was hence proposed for oil migration (Fetter et al., submitted), taking into account the key role of deep-seated waters circulating through the sedimentary basin by calling on a long-neglected phenomenon: mutual solubility of water and oil at high temperatures.Bringing to light the complex dynamics of Pb in crude oil invalidates the use of crude oil as an alternative to K-feldspars to obtain the Pb isotopic signature of the continental crust underlying sedimentary basins. However, it opens up new promising avenues for the yet unexplored use of Pb isotopes as tracers of irresponsible oil prospection related pollution.

Sedimentary rocks are characterized with very low permeability (in the order of 10-22 m2), low diffusivity, a possible self-healing of fractures, and a good capacity to retard radionuclide transport. In recent years, sedimentary rocks are investigated by many research groups for their suitability for the disposal of radioactive waste. Development of deep geologic repositories (DGRs) for the storage of radioactive waste within these formations causes progressive modification to the state of stress, to the groundwater regime, and to the chemistry of the rock mass. Thermal effects due to the ongoing nuclear activity can cause additional disturbances to the system. All these changes in the system are coupled and time-dependent processes. These coupled processes can result in the development of an excavation damaged zone (EDZ) around excavations. More permeable than the undisturbed rock, the EDZ is likely to be a preferential pathway for water and gas flow. Consequently, the EDZ could be a potential exit pathway for the radioactive waste to biosphere. An investigation of the Hydraulic-Mechanical (HM) and Thermal-Hydraulic-Mechanical-Chemical (THMC) behaviour of sedimentary rock formations is essential for the development of DGRs within such formations. This research work consists of (1) an experimental investigation of the mechanical behaviour of the anisotropic Tournemire argillite, (2) modeling of the mechanical behaviour of the Tournemire argillite, and (3) numerical simulations of the mechanical and hydromechanical behavior of two host sedimentary rocks, the Tournemire argillite and Cobourg limestone, for deep geological repository for nuclear wastes. The experimental program includes the measurements of the physical properties of the Tournemire argillite and its mechanical response to loading during uniaxial compression tests, triaxial compression tests with different confining pressures, unconfined and confined cyclic compression tests, Brazilian tests, and creep tests. Also, acoustic emission events are recorded to detect the initiation and propagation of microcracks within the rock during the uniaxial testing. The approach for modeling the mechanical behaviour of the Tournemire argillite consists of four components: elastic properties of the argillite, a damage model, the proposed concept of mobilized strength parameters, and the classical theory of elastoplasticity. The combination of the four components results in an elastoplastic-damage model for describing the mechanical behaviour of the Tournemire argillite. The capabilities of the model are evaluated by simulating laboratory experiments. Numerical simulations consist of: (1) a numerical simulation of a mine-by-test experiment at the Tournemire site (France), and (2) numerical simulations of the mechanical and hydromechanical behaviour of the Cobourg limestone within the EDZ (Canada). The parameters influencing the initiation and evolution of EDZ over time in sedimentary rocks are discussed.

Sedimentary rocks are characterized with very low permeability (in the order of 10-22 m2), low diffusivity, a possible self-healing of fractures, and a good capacity to retard radionuclide transport. In recent years, sedimentary rocks are investigated by many research groups for their suitability for the disposal of radioactive waste. Development of deep geologic repositories (DGRs) for the storage of radioactive waste within these formations causes progressive modification to the state of stress, to the groundwater regime, and to the chemistry of the rock mass. Thermal effects due to the ongoing nuclear activity can cause additional disturbances to the system. All these changes in the system are coupled and time-dependent processes. These coupled processes can result in the development of an excavation damaged zone (EDZ) around excavations. More permeable than the undisturbed rock, the EDZ is likely to be a preferential pathway for water and gas flow. Consequently, the EDZ could be a potential exit pathway for the radioactive waste to biosphere. An investigation of the Hydraulic-Mechanical (HM) and Thermal-Hydraulic-Mechanical-Chemical (THMC) behaviour of sedimentary rock formations is essential for the development of DGRs within such formations. This research work consists of (1) an experimental investigation of the mechanical behaviour of the anisotropic Tournemire argillite, (2) modeling of the mechanical behaviour of the Tournemire argillite, and (3) numerical simulations of the mechanical and hydromechanical behavior of two host sedimentary rocks, the Tournemire argillite and Cobourg limestone, for deep geological repository for nuclear wastes. The experimental program includes the measurements of the physical properties of the Tournemire argillite and its mechanical response to loading during uniaxial compression tests, triaxial compression tests with different confining pressures, unconfined and confined cyclic compression tests, Brazilian tests, and creep tests. Also, acoustic emission events are recorded to detect the initiation and propagation of microcracks within the rock during the uniaxial testing. The approach for modeling the mechanical behaviour of the Tournemire argillite consists of four components: elastic properties of the argillite, a damage model, the proposed concept of mobilized strength parameters, and the classical theory of elastoplasticity. The combination of the four components results in an elastoplastic-damage model for describing the mechanical behaviour of the Tournemire argillite. The capabilities of the model are evaluated by simulating laboratory experiments. Numerical simulations consist of: (1) a numerical simulation of a mine-by-test experiment at the Tournemire site (France), and (2) numerical simulations of the mechanical and hydromechanical behaviour of the Cobourg limestone within the EDZ (Canada). The parameters influencing the initiation and evolution of EDZ over time in sedimentary rocks are discussed.