Gas hydrate is a naturally occurring crystalline compound formed by water molecules and encapsulated gas molecules. The interest in gas hydrate reflects scientific, energy and safety concerns - climate change, future energy resources and seafloor stability. Gas hydrates form in the pore space of sediments, under high pressure and low temperature conditions. This research focuses on the fundamental understanding of hydrate bearing sediments, with emphasis on mechanical behavior, thermal properties and lens formation. Load-induced cementation and decementation effects are explored with lightly cemented loose and dense soil specimens subjected to ko-loading; the small-strain stiffness evolution inferred from shear wave velocity measurement denounces stiffness loss prior to structural collapse upon loading. Systematic triaxial tests address the intermediate and large strain response of hydrate bearing sediments for different mean particle size, applied pressure and hydrate concentration in the pore space; hydrate concentration determines elastic stiffness and undrained strength when Shyd>45%. A unique sequence of particle-level and macro-scale experiments provide new insight into the role of interparticle contact area, coordination number and pore fluid on heat transfer in particulate materials. Micro-mechanisms and necessary boundary conditions are experimentally analyzed to gain an enhanced understanding of hydrate lens formation in sediments; high specific surface soils and tensile stress fields facilitate lens formation. Finally, a new instrumented high-pressure chamber is designed, constructed and field tested. It permits measuring the mechanical and electrical properties of methane hydrate bearing sediments recovered from pressure cores without losing in situ pressure (~20MPa).

Studying clathrate hydrates is, ideally, a simple task: one just have to keep water under a gas pressure. However, when trying to collect measurements in an accurate and repeatable way, things mess up. When, in particular, kinetic characterizations are required, not only pressure and temperature have to be measured: also particular parameters such as gas evolved/trapped during time, heat released/adsorbed during time, critical phenomena related to additive addition, etc, should be collected in a finer way. In the last years a growing interest has been devoted to investigations on the effects of a wide range of compounds capable to affect the thermodynamics and, in particular, kinetics of clathrate hydrate formation. The study of the effects of these compounds, called conditioners, requires an improvement of the performances of usual lab facilities by introducing a new strategy for the measurement of further characterizing parameters. Presently no standardization of the apparatus designed for clathrate hydrate studies exists, nor any commercial instrumentations are available. Generally, apparatus used are custom-made by the same research team according with the peculiar research requirements To do this we have designed, built, calibrated and tested a novel apparatus that, in addition to the ability of measuring usually unexplored parameters, is based on the idea of obtaining as many parameters as possible in a single formation batch. This in order to solve the problem of collecting a dataset that can be processed homogeneously, thus minimizing errors due stochastic behaviours. Using such an apparatus, several kinds of measurement are presented here, which are related directly to the clathrate hydrate investigation fields, but also more generally related to the study of equilibrium phases involving gaseous components.

Carbon dioxide hydrates were synthesized in a 0.10m I.D. and 1.22m tall bubble column equipped with a cooling jacket for heat removal. Visual observations at different driving forces (pressures between 2.75 and 3.60 MPa and temperatures between 0 and 8ºC) were recorded with a digital camera through a sight glass of 118.8 by 15.6 mm. The superficial gas velocity was varied from 20 to 50 mm/s to attain different levels of turbulence in the liquid. The growth rate was found to be dependent on the sequence/method used to reach the operating temperature and pressure. A greater supersaturation was obtained when the system temperature and pressure were reached with very low or no bubble-induced mixing. As a result, hydrates nucleated and grew immediately when starting the gas flow with the reactor volume being quickly filled with hydrates. Moreover, the hydrate growth rate and solution final density were higher when operating conditions partially condensed CO2 resulting in greater interphase mass transfer rates. In parallel, since hydrate formation is an exothermic process and the reaction is often limited by the rate of heat removal, heat transfer measurements were achieved in a simulated hydrate environment. The instantaneous heat transfer coefficient and related statistics gave insight on the role of bubbles on heat transfer and hydrodynamics.

Capturer le CO2 est devenu un domaine de recherche important en raison principalement des forts effets de serre dont il est jugé responsable. La formation d'hydrate de gaz comme technique de séparation montre un potentiel considérable, d'une part pour sa faisabilité physique et d'autre part pour une consommation énergétique réduite. En bref, les hydrates de gaz (clathrates) sont des composés ″cages″ non-stoechiométriques, cristallins comme la glace et formés par une combinaison de molécules d'eau et de molécules hôtes convenables, à basses températures et pressions élevées. Puisque la pression exigée pour la formation d'hydrate de gaz est généralement forte, il est judicieux d'ajouter du bromure tétra-n-butylique d'ammonium (TBAB) comme promoteur de formation d'hydrate de gaz. En effet, le TBAB permet généralement de réduire la pression exigée et/ou d'augmenter la température de formation aussi que de modifier la sélectivité des cages d'hydrates au profit des molécules de CO2. TBAB participe à la formation des cages par liaisons ″hydrogène″. De tels hydrates sont nommés "semi-clathrate hydrates". Évidemment, des données d'équilibres de phase fiables et précises, des modèles thermodynamiques acceptables, et d'autres études thermodynamiques sont requises pour concevoir des procédés de séparation efficaces utilisant la technologie mentionnée ci-dessus. Dans ce but, des équilibres de phase de clathrate/semi-clathrate hydrates de de divers mélanges avec des gaz contenant CO2 (CO2 + CH4/N2/H2) ont été mesurés, ici, en présence d'eau pure et de solutions aqueuses de TBAB. La partie théorique de la thèse présente un modèle thermodynamique développé avec succès sur la base de la théorie des solutions solides de van der Waals et Platteeuw (vdW-P) associée aux équations modifiées de la détermination des constantes de Langmuir des promoteurs d'hydrates pour la représentation/prédiction des équilibres en présence de ″semi-clathrate hydrates″ de CO2, CH4, et N2. Plusieurs tests de cohérence thermodynamique basés soit sur l'équation de Gibbs-Duhem, soit sur une approche statistique ont été appliqués aux données d'équilibre de phase des systèmes de ″clathrate hydrates″ simples/mélanges afin de statuer sur leur qualité. / CO2 capture has become an important area of research mainly due to its drastic green-house effects. Gas hydrate formation as a separation technique shows tremendous potential, both from a physical feasibility as well as an envisaged lower energy utilization criterion. Briefly, gas (clathrate) hydrates are non-stoichiometric, ice-like crystalline compounds formed through a combination of water and suitably sized guest molecule(s) under low-temperatures and elevated pressures. As the pressure required for gas hydrate formation is generally high, therefore, aqueous solution of tetra-n-butyl ammonium bromide (TBAB) is added to the system as a gas hydrate promoter. TBAB generally reduces the required hydrate formation pressure and/or increases the formation temperature as well as modifies the selectivity of hydrate cages to capture CO2 molecules. TBAB also takes part in the hydrogen-bonded cages. Such hydrates are called "semi-clathrate" hydrates. Evidently, reliable and accurate phase equilibrium data, acceptable thermodynamic models, and other thermodynamic studies should be provided to design efficient separation processes using the aforementioned technology. For this purpose, phase equilibria of clathrate/semi-clathrate hydrates of various gas mixtures containing CO2 (CO2 + CH4/N2/H2) in the presence of pure water and aqueous solutions of TBAB have been measured in this thesis. In the theoretical section of the thesis, a thermodynamic model on the basis of the van der Waals and Platteeuw (vdW-P) solid solution theory along with the modified equations for determination of the Langmuir constants of the hydrate formers has been successfully developed to represent/predict equilibrium conditions of semi-clathrate hydrates of CO2, CH4, and N2. Later, several thermodynamic consistency tests on the basis of Gibbs-Duhem equation as well as a statistical approach have been applied on the phase equilibrium data of the systems of mixed/simple clathrate hydrates to conclude about their quality.

Les hydrates de gaz sont des cristaux composés de molécules d’eau formant des cages, piégeant des molécules de gaz. A l’état naturel, ces hydrates se forment en présence de mélanges gazeux dans les fonds océaniques et seraient impliqués dans la formation des comètes et des planètes. Comprendre la sélectivité moléculaire et la stabilité des hydrates mixtes (co-incluant plusieurs espèces gazeuses) est primordiale et constitue le coeur de ce travail de doctorat. En s’appuyant sur la spectroscopie Raman et la diffraction des neutrons, complétés de calculs de chimie quantique, les hydrates formés à partir de mélanges de CO, N2 et de CO2 ont été étudiés.Outre leur intérêt astrophysique, ces systèmes permettent d’appréhender l’impact de propriétés physico-chimiques (moment dipolaire,solubilité, adsorption sur la glace) sur la sélectivité.La cinétique de formation et les signatures vibrationnelles des molécules encapsulées dans différents types de cages ontété analysées pour la première fois dans les hydrates purs de CO et de N2. En variant pression et température, une capacité exceptionnelle de diffusion des molécules gazeuses à travers les cages est révélée. La sélectivité moléculaire, la stabilité structurale et l’occupation des cages ont été étudiées dans les hydrates mixtes CO-N2, CO-CO2 et CO2-N2.L’affinité aqueuse et le moment dipolaire des molécules gazeuses pilotent la sélectivité des gaz piégés (encapsulation préférentielle du CO et du CO2). De plus, l’azote joue un rôle de promoteur cinétique des structures formées. Ces résultats fondamentaux ouvrent de nouvelles perspectives tant appliquées (séparation des gaz) que fondamentales (hydrates en milieu naturel). / Gas hydrates are crystalline compounds consisting of water molecules forming cages within which gas molecules are encapsulated. In natural environments, gas hydrates are formed in the presence of gaseous mixtures in the ocean floor and would be involved in the formation of comets and planets. Understanding the molecular selectivity and the stability of mixed hydrates (co-including several gaseous species) is crucial and constitutes the core of this research work. With the help of Raman spectroscopy and neutron diffraction,supplemented by quantum chemistry calculations, hydrates formed from mixtures of CO, N2 and CO2 have been investigated. In addition to their astrophysical interest, these systems offer the opportunity to better understand the impact of physical-chemistry properties (dipolar moment, water solubility,adsorption on ice) on the selectivity.The formation kinetics and the vibrational signatures of the encapsulated molecules in various types of cage have been analyzed in pure CO and N2 hydrates for the first time. By varying pressure and temperature, the gaseous molecules exhibit an exceptional ability for diffusing through the cages. Molecular selectivity, structural stability and cage occupancy have been studied in the mixed hydrates CO-N2, CO-CO2 and CO2-N2. The aqueous affinity and the dipolar moment of the gas molecules trigger the selectivity of the trapped gases (preferential encapsulation of COand CO2). In addition, the nitrogen molecule acts as a kinetic promoter of the formed structure. These fundamental results open new opportunities on both applied (gas separation)and fundamental (hydrates in natural environment) aspects.

Les hydrates de gaz sont des composés cristallins stables à haute pression et à basse température, très répandus sur terre, notamment dans les fonds marins au niveau des marges continentales, où ils contribuent à la stabilité des sédiments par leur cohésion et leur adhésion aux surfaces minérales. Cependant, le comportement mécanique des hydrates en soi a été peu ou pas étudié à l’échelle du pore. L’objectif de cette thèse est d’étudier les conditions de stabilité et les propriétés mécaniques en traction de l’hydrate de méthane à l’échelle du pore, dans une configuration comparable à celle qu’on peut trouver dans les milieux poreux sédimentaires.Ici, nous étudions d’abord par microscopie optique les conditions de formation, de croissance et de dissociation de l’hydrate de méthane à l’interface eau/CH4 dans un micro-capillaire en verre utilisé à la fois comme un pore modèle et comme une cellule optique résistante à haute pression et à basse température. Ensuite, en développant une méthode originale in situ et sans contact : "dépression thermo-induite" on détermine les propriétés mécaniques en traction d’une coquille polycristalline d’hydrate de méthane. L’hydrate est nucléé à basse température sur l’interface eau/CH4, qui est rapidement recouverte d’une "croûte" polycristalline d’hydrate. À partir de cette croûte, l’hydrate pousse de part et d’autre de l’interface : dans l’eau sous forme "d’aiguilles" cristallines, dans le gaz, sous forme de "filaments" cristallins, et enfin entre le substrat et le gaz sous forme d’un "halo". Le halo qui est un film polycristallin avançant sur le substrat, en chevauchant un film d’eau, ralentit et finit par s’immobiliser et s’accrocher au substrat. À partir de ce moment, "la coquille" polycristalline, constituée de la croûte et du halo, forme une barrière entre l’eau et le gaz. Les tests de traction sont effectués par génération d’une dépression dans le compartiment eau en augmentant la température à pression de méthane constante.Les propriétés élastiques en traction de la coquille (module élastique et contrainte de rupture) sont déterminées en fonction de la taille des grains, contrôlée ici par les deux paramètres : le sous-refroidissement par rapport à la température d’équilibre, et le temps de mûrissement. On trouve un comportement élastoplastique à caractères ductile et fragile mélangés. Nos données de contrainte de rupture s’insèrent dans un écart de cinq ordres de grandeurs de taille de grain, et de trois ordres de grandeurs de la contrainte de rupture (entre des données de simulation à l’échelle nanomètrique et des données expérimentales à l’échelle millimétrique). L’effet de taille de grain sur la contrainte de rupture de l’hydrate de méthane peut être un facteur contribuant à la déstabilisation des pentes continentales. / Gas hydrates are ice-like crystals stable at high pressure and low temperature. They are ubiquitous on earth, notably at the edges of continental shelves, where they contribute to the mechanical stability of marine sediments, by hydrate cohesion and hydrate adhesion to mineral particles. However, the mechanical behavior of gas hydrates at pore scale has been hardly or not at all studied. The purpose of this thesis is to study the stability conditions and the tensile mechanical properties of methane hydrate at pore scale in a representative pore habit of gas hydrate in a sedimentary medium.Here, using optical microscopy, first the formation, growth and dissociation conditions of methane hydrate are investigated across a water/CH4 interface in glass micro-capillaries used both as a pore model and as an optical cell resisting high pressure and low temperature. Then by developing a contactless and an in situ method, "thermally induced depressing", tensile mechanical properties of polycrystalline methane hydrate shell are determined. At low enough temperature, the hydrate nucleates as a polycrystalline "crust" over the water/CH4 interface. From this crust, the hydrate continues growing on both sides of the interface: in the water as "needle like crystals", in the gas as "hair like crystals", and finally between the gas and the substrate as a polycrystalline film, the "halo". The halo advances slowly on the substrate, riding over a water film, and comes to rest and adheres to the substrate. From then on, the "shell" (crust and halo) isolates the water from the gas. Tensile tests are carried out by generating a depression in the water compartment by increasing temperature at constant methane pressure.Tensile elastic properties of the shell (elastic modulus and the tensile strength) are determined as a function of the grain size, controlled here by two parameters, supercooling compared to the equilibrium temperature and the annealing time. We find elastoplastic behavior, with mixed ductile and brittle characteristics. Our data on tensile strength contribute to fit the gap of five orders of magnitude of grain size, and three orders of magnitude of tensile strength (between molecular simulations at nanometre scale and current experiment at millimetre to centimetre scale). The effect of grain size on the tensile strength of methane hydrate could be a factor contributing to the destabilization of continental slopes.

Die Delamination beschreibt einen glaskorrosiven Angriff, bei welchem dünne, plättchenförmige Partikel im angreifenden Medium vorhanden sind. Ziel dieser Arbeit ist die Analyse der zu Grunde liegenden Reaktionsmechanismen. Nahezu jedes der untersuchten silikatischen Glassysteme zeigt Delamination. Notwendige Bedingungen sind das Vorhandensein von Magnesiumionen sowie eine ausreichende Auflösung des Glasnetzwerkes zur Bereitstellung der Reaktionspartner. Es kommt zur Bildung einer magnesiumreichen Schicht auf der Glasoberfläche, welche sich ablöst. Die Delaminationsprodukte sind teilweise kristallin. Als Hauptphase wird das Magnesiumsilikat-Hydrat Talk nachgewiesen. Es wirken weitere Elemente delaminationsfördernd, darunter die Erdalkalimetalle höherer Ordnungszahl, außerdem Eisen und Mangan sowie Lithium. Eine hemmende Wirkung besitzen die Elemente der dritten Haupt- und Nebengruppe des Periodensystems, insbesondere Bor, Aluminium und Yttrium sowie Beryllium. Die Delamination ist nur einer von zahlreichen Teilschritten der Glaskorrosion mit Phasenneubildung.

Carbon dioxide hydrates were synthesized in a 0.10m I.D. and 1.22m tall bubble column equipped with a cooling jacket for heat removal. Visual observations at different driving forces (pressures between 2.75 and 3.60 MPa and temperatures between 0 and 8ºC) were recorded with a digital camera through a sight glass of 118.8 by 15.6 mm. The superficial gas velocity was varied from 20 to 50 mm/s to attain different levels of turbulence in the liquid. The growth rate was found to be dependent on the sequence/method used to reach the operating temperature and pressure. A greater supersaturation was obtained when the system temperature and pressure were reached with very low or no bubble-induced mixing. As a result, hydrates nucleated and grew immediately when starting the gas flow with the reactor volume being quickly filled with hydrates. Moreover, the hydrate growth rate and solution final density were higher when operating conditions partially condensed CO2 resulting in greater interphase mass transfer rates. In parallel, since hydrate formation is an exothermic process and the reaction is often limited by the rate of heat removal, heat transfer measurements were achieved in a simulated hydrate environment. The instantaneous heat transfer coefficient and related statistics gave insight on the role of bubbles on heat transfer and hydrodynamics.

The mass of carbon trapped in methane hydrates exceeds that in conventional fossil fuel reservoirs. While methane in coarse-grained hydrate-bearing sediments is technically recoverable, most methane hydrates are found in fine-grained marine sediments where gas recovery is inherently impeded by very low gas permeability. Using experimental methods and analyses, this thesis advances the understanding of fine-grained sediments in view of gas production from methane hydrates. The research scope includes: a new approach for the classification of fines in terms of electrical sensitivity, the estimation of the sediment volume contraction during hydrate dissociation, a pore-scale study of gas migration in sediments and the self-regulation effect of surfactants, the formation of preferential gas migration pathways at interfaces during gas production, pressure core technology for the characterization of hydrate bearing sediments without causing hydrate dissociation, and the deployment of a bio-sub-sampling chamber in Japan.

Statybos pramonėje, mišiniuose vis plačiau naudojamas įvairus tiek natūralių tiek sintetinių ceolitų spektras. Atliktuose tyrimuose buvo naudojamas sintetinis ceolitas – hidrosodalitas (Na6+x(SiAlO4)6(OH)x•nH2O), modifikuotas hidrosodalitas ir fero silicio gamybos atlieka - SiO2 mikrodulkės. Su pastaraisiais pucolaniniais priedais tiriama sąveika su cementu, nustatyta kaip keičiasi cemento stiprio, tankio ir įgėrio savybės. Tyrimai atlikti ruošiant bandinius su 2%, 5%, 10% ir 15% pucolaninių priedų masės santykiais. Atlikus tyrimus nustatyta, kokia daroma įtaka cementinės masės hidratacijos temperatūrai. Nustatytas bandinių stiprumas, tankis po 3, 7 ir 28 parų. Nustatytas bandinių įgėris po 28 parų. Cementinio akmens gniuždomasis stipris nenaudojant priedo ir ilginant hidratacijos trukmę nuo 3 iki 28 parų didėja nuo 59 iki 80 MPa. Panaši priklausomybė stebima ir cementiniuose bandiniuose su pucolaniniais priedais. Ilgėjant hidratacijos trukmei stipriai gniuždant didėja. Tirtose sąlygose didžiausią stiprį gniuždant turėjo bandiniai su 10 % modifikuoto hidrosodalito priedo po 28 parų, gniuždomasis stipris padidėja iki 101 MPa. Galima daryti prielaidą, kad hidrosodalito, modifikuoto hidrosodalito ir SiO2 mikrodulkių pucolaninės savybės pasireiškia ne iš karto, bet išryškėja po ilgesnes hidratacijos trukmės, t. y. po 28 parų. Vykstant hidratacijai nuo 16 iki 28 parų, įgėris sumažėja nuo 13,41% iki 9,04% (esant 2% hidrosodalito kiekiui). Naudojant 5% SiO2 mikrodulkių kiekį... [toliau žr. visą tekstą] / Construction industry is increasingly being used in combination and variety of natural and synthetic zeolites spectrum. A study carried out using synthetic zeolite - hydrasodalite (Na6 + x (SiAlO4) 6 (OH) x • nH2O) modified hydrasodalite silicon production and Fair play - fume SiO2. With the recent pozzolanic additives investigated the interaction with cement, concrete changes in the strength, density and retention properties. Studies carried out in the preparation of the samples with 2%, 5%, 10% and 15% by weight of pozzolanic additives relations. It was determined, which affect the weight of cement hydration temperature. Fixed specimens the strength and the density of 3, 7 and 28 days. Set of samples absorption after 28 days. Compressive strength of cement stone without the use of additive and longer duration of hydration from three to 28 days increased from 59 to 80 MPa. A similar dependence is observed in samples with cement and pozzolanic additives. Hydration with increasing duration of the compressive strength increases. To examine the conditions had the highest compressive strength of samples with 10% modified hydrasodalite additives after 28 days, compressive strength increases to 101 MPa. It can be assumed that hydrasodalite, and SiO2 modified hydrasodalite fume pozzolanic properties are not immediate, but come on after a longer duration of hydration, etc. Y. after 28 days. During the hydration from 16 to 28 days, absorption decreases from 13.41% to 9.04% (at 2%... [to full text]