El objetivo principal de esta investigación se centra en el análisis de los efectos de la temperatura y la hidratación o secado de las arcillas en el comportamiento de cambio de volumen, permeabilidad y características de retención de agua, ante una variedad de trayectorias de succión, tensión neta y temperatura. Se han utilizado dos muestras de arcilla de Boom (Mol, Bélgica) artificialmente preparadas con una estructura dominante de agregados y exhibiendo pautas de comportamiento extremas de las arcillas parcialmente saturadas. Las muestras artificiales se han caracterizado extensamente con relación a los aspectos hidráulicos y mecánicos, tanto desde el punto de vista micro-estructural como a escala macro-estructural, donde se identifican dos zonas claras de dominio de la succión a nivel 'intra-agregado' o a nivel 'inter-agregado'. <br/><br/>Se han diseñado y construido nuevas células edométricas y un equipo triaxial con control de temperatura y succión. La célula triaxial permite registrar la evolución temporal de las deformaciones axiales (a través de LVDT locales), de las deformaciones radiales y de las isócronas de los perfiles laterales (a través de sensores láser), que experimenta la muestra en diferentes trayectorias mecánicas, de hidratación y de temperatura. En la técnica de sobre-presión de aire se ha mantenido una presión constante, aplicándola inicialmente en condiciones de fase de aire continua. La temperatura se limitó a un máximo de 80°C para evitar cambios de fase y químicos apreciables, así como para limitar los problemas asociados a la técnica de traslación de ejes. Se llevaron a cabo dos tipos de ensayos: las trayectorias en condiciones isotérmicas a dos temperaturas contrastantes y los ensayos en condiciones no isotérmicas. Los ensayos isotérmicos se enfocaron en trayectorias de humedecimiento y de secado bajo tensiones netas verticales y medias constantes, en ciclos de carga y descarga a succión constante, así como en ensayos isócoros a succión controlada. <br/><br/>Los ensayos sobre muestras altamente sobreconsolidadas revelaron un hinchamiento irreversible en las trayectorias de calentamiento a succión constante, debido a una reestructuración del esqueleto de la arcilla asociada a un mecanismo de adsorción de agua. Los resultados no isotermos mostraron valores similares ante cambios de volumen y contenidos de agua a los obtenidos bajo condiciones isotérmicas en trayectorias de humedecimiento a diferentes temperaturas y estados tensionales equivalentes. La existencia de deformaciones plásticas y de cambios irreversibles en el contenido de agua, asociados con las trayectorias principales de hidratación y de secado, es un aspecto relevante de los resultados, siendo más importante a temperaturas elevadas. Los resultados a succión controlada y tensión neta media constante revelaron una contracción irreversible durante el calentamiento de una muestra de arcilla normalmente consolidada. Asimismo se identifica una zona de máximo colapso en las trayectorias isotérmicas de humedecimiento bajo tensión neta vertical constante realizadas sobre las muestras de alta porosidad. Los ensayos isócoros sobre las muestras de baja porosidad mostraron un hinchamiento dominante, asociado a una presión de hinchamiento mayor que la registrada por las muestras de alta porosidad, donde se detecta un colapso macroestructural compensado por la expansión reversible de la estructura. Basándose en estas observaciones, se han propuesto hipótesis para explicar las pautas de comportamiento desde el punto de vista de los diferentes fenómenos micro y macroscópicos que afectan a las arcillas no saturadas. Se han planteado una serie de expresiones para las curvas de retención y permeabilidad al agua a diferentes temperaturas, porosidades y grados de saturación. Los cambios producidos por la acción mecánica, la succión y la temperatura se han interpretado bajo un concepto elastoplástico utilizando diferentes variables de estado tensionales y sus correspondientes variables conjugadas extensivas. In view of the increasing use of clay in high-temperature environments, mainly related to the conceptual design of engineered barriers for radioactive waste disposal in deep geological media, and to enrich the existing body of knowledge in the thermo-hydro-mechanical response, a systematic laboratory research programme has been designed and carried out to investigate these aspects. The main objective of this research is to analyse the effects of temperature and hydration or drying paths on clay volume change behaviour, water permeability and water retention characteristics, under a variety of matric suction, net stress and temperature paths. Two artificially prepared packings of Boom clay powder with a dominant aggregated fabric, covering a wide overconsolidation range, have been used in the testing programme. Clay powder and artificially prepared samples have been extensively characterised in relation to hydraulic and mechanical aspects, both at microstructural and macrostructural scale.<br/> <br/>New temperature and suction controlled oedometer cells and triaxial equipment have been designed, developed and carefully calibrated for investigating mechanical and thermal aspects of behaviour. The fully instrumented triaxial cell allows registering the time evolution of axial strains (via internal LVDTs), radial deformations and isochrones of lateral profiles (via electro-optical laser sensors) that experiences the sample under different mechanical, hydration and temperature paths. Air overpressure technique maintaining a constant air pressure has been followed during the tests, starting from continuous air phase conditions. Maximum temperature has been limited to 80°C for no appreciable phase and chemical change to occur, as well as to limit spurious problems affecting axis translation technique. Two main test types were carried out: isothermal tests at two different temperatures and non-isothermal paths. Isothermal paths were focused on wetting and drying cycles at constant net vertical or mean stress and loading-unloading cycles at constant suction, as well as suction controlled isochoric swelling/shrinkage pressure tests.<br/> <br/>Reversible and irreversible features of volume change behaviour (swelling, collapse and shrinkage, thermal dilatation and contraction), under oedometer and isotropic stress state conditions have been observed. Tests on heavily overconsolidated states revealed irreversible expansion upon drained heating at constant suction due to a structural rearrangement of clay skeleton, giving similar values in terms of volume and water content changes compared to isothermal wetting paths at different temperatures and equivalent stress states. The existence of important plastic deformations and irreversible water content changes associated with the first suction reduction and main drying path is a relevant feature of the data, which is more important at higher temperatures. Testing results at constant suction and net mean stress show that temperature increase on an open normally consolidated structure revealed irreversible contraction. A maximum collapse/contraction zone is also identified in the isothermal wetting paths at constant net vertical stress performed on the high-porosity fabrics. Isochoric tests revealed a dominating swelling for the low-porosity sample, where a higher swelling pressure is detected, and a controlling macrostructural collapse compensated by the reversible expansion of the structure for the high-porosity fabric. Based on these observations, hypotheses are proposed to explain features of behaviour in terms of microscopic and macroscopic phenomena affecting unsaturated clays. Expressions for retention curves and water permeability functions at different temperatures, as well as values of the different parameters describing porosity, temperature and degree of saturation dependence, have been proposed and determined for both fabrics under a variety of conditions. Mechanical, suction and thermal induced changes in terms of different stress state variables and their associated work conjugate variables were discussed within an elastoplastic point of view, and parameters characterising their reversible and irreversible features respect to drained and undrained thermal coefficients, as well as suction decrease, suction increase and loading-collapse yield loci, determined.

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Many shales previously thought of as only source rocks are now recognized as self-sourcing reservoirs that contain large volumes of natural gas and liquid hydrocarbons that can be produced using horizontal drilling and hydraulic fracturing. However, shale gas resources and development economics are uncertain, and these uncertainties beg for a probabilistic solution. Our objective was to probabilistically determine the distribution of technically recoverable resources (TRR) and shale original gas in place (OGIP) in highly uncertain and risky shale gas reservoirs for seven world regions. To assess technically recoverable resources, we used the distribution of recovery factors from shale gas reservoirs. We developed a software, Unconventional Gas Resource Assessment System (UGRAS), which integrates Monte Carlo simulation with an analytical reservoir simulator to establish the probability distribution of OGIP and TRR. We used UGRAS to evaluate the most productive shale gas plays in the United States, including the Barnett, Eagle Ford, Marcellus, Fayetteville, and Haynesville shales, and derived a representative distribution of recovery factors for shale gas reservoirs. The recovery factors for the five shale gas plays follow a general Beta distribution with a mean value of 25%. Finally, we extended the distribution of recovery factors gained from our analyses of shale gas plays in the U.S. to estimate technically recoverable shale-gas resources for the seven world regions. Total technically recoverable shale gas resources are estimated to range from 4,000 Tcf (P90) to 24,000 Tcf (P10). UGRAS is a robust tool that may be used to evaluate and rank shale-gas resources worldwide. This work provides important statistics for the five most productive shale-gas plays in the United States. Results of this work verify the existence of significant technically recoverable shale gas resources worldwide and can help industry better target its exploitation efforts in shale-gas plays.