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A major part of the terrestrial sediment in the ocean comes from the land via river plume. There are four stages in sediment dispersal from rivers into the sea: supply via plume, initial deposition, resuspension and transport by waves and currents or by the slope failure, and long-term net accumulation. We can understand the dispersion and transport of the river plume by in situ observations of hydrodynamic of the plume field. Therefore, it is helpful to study river plume hydrodynamics, such as winds, tides, waves, and currents. The purpose of this study is to identify the type of plume dynamics by analyzing the temporal and spatial variability of hydrological structures observed around the Gaoping River mouth. We observed the bottom and surface time series of temperature, salinity, turbidity, suspended sediment concentration, and velocity profile by instrument mounted at the tetrapods and a moored buoy during July 28 to 30 in 2009 and July 30 to August 2 in 2011. Besides, we investigated the spatial structures of the river plume in Gaoping River mouth by using a fishing boat in 2009. We also acquired satellite images to assist our study. The results showed that the river discharges during 2009 was lower than daily average discharge. Combined the temporal and spatial observations and satellite images, we determined that the river plume turned west during the ebb tide was influenced by Coriolis force and winds. The buoyancy-driven current velocity was 0.15 m/s and the maximum of wind-driven current velocity was 0.30 m/s. The wind strength index (Ws) determines whether a plume¡¦s along-shelf flow is in a wind-driven or buoyancy-driven state. Ws is the ratio of the wind-driven and buoyancy-driven along-shelf velocities. If |W_s | > 1 on average the wind velocity more than 5.9 m/s. The wind velocity reached this threshold during most of the ebb periods, and around that value in the flood time. Flood currents combined with cross-shore wind pushed the river plume to swing to the east. The data were analyzed by empirical orthogonal function (EOF) analysis. The results indicated that winds and waves were the main factors influencing plume dynamics during low-discharge period. During the field experiment in 2011, the river discharge was greater than daily average discharge. The buoyancy-driven and the maximum of wind-driven current velocities were 0.30 and 0.12 m/s, respectively. The wind velocity did not reach the threshold that was 11.67 m/s. The buoyancy-driven current was more significant than wind-driven current. By analyzing the ocean color of satellite images, the river plume was spreading from the river mouth and toward west during ebb. The time series data also showed that there was plume signal at the same time. The average cross-shore current velocity was 0.52 m/s, being larger than the buoyancy-driven current. Therefore, the tide was the main factor deciding where the plume discharged. The first eigemode of EOF suggested that current was the most important factor influencing plume dynamics during high-discharge period. The second eignmode described the dominant influence of wind.

Geological sequestration of CO₂ in deep saline reservoirs is one of the ways to reduce its continuous emission into the atmosphere to mitigate the greenhouse effect. The effectiveness of any CO₂ sequestration operation depends on pore volume and the sequestration efficiency of the reservoir. Sequestration efficiency is defined here as the maximum storage with minimum risk of leakage to the overlying formations or to the surface. This can be characterized using three risk parameters i) the time the plume takes to reach the top seal; ii) maximum lateral extent of the plume and iii) the percentage of mobile CO₂ present at any time. The selection among prospective saline reservoirs can be expedited by developing some semi-analytical correlations for these risk parameters which can be used in place of reservoir simulation study for each and every saline reservoir. Such correlations can reduce the cost and time for commissioning a geological site for CO₂ sequestration. To develop such correlations, a database has been created from a large number of compositional reservoir simulations for different elementary reservoir parameters including porosity, permeability, permeability anisotropy, reservoir depth, thickness, dip, perforation interval and constant pressure far boundary condition. This database is used to formulate different correlations that relate the sequestration efficiency to reservoir properties and operating conditions. The various elementary reservoir parameters are grouped together to generate different variants of gravity number used in the correlations. We update a previously reported correlation for time to hit the top seal and develop new correlations for other two parameters using the newly created database. A correlation for percentage of trapped CO₂ is also developed using a previously created similar database. We find that normalizing all risk parameters with their respective characteristic values yields reasonable correlations with different variants of gravity number. All correlations confirm the physics behind plume movement in a reservoir. The correlations reproduce almost all simulation results within a factor of two, and this is adequate for rapid ranking or screening of prospective storage reservoirs. CO₂ injection in saline reservoirs on the scale of tens of millions of tonnes may result in fracturing, fault activation and leakage of brine along conductive pathways. Critical contour of overpressure (CoP) is a convenient proxy to determine the risk associated with pressure buildup at different location and time in the reservoir. The location of this contour varies depending on the target aquifer properties (porosity, permeability etc.) and the geology (presence and conductivity of faults). The CoP location also depends on relative permeability, and we extend the three-region injection model to derive analytical expressions for a specific CoP as a function of time. We consider two boundary conditions at the aquifer drainage radius, constant pressure or an infinite aquifer. The model provides a quick tool for estimating pressure profiles. Such tools are valuable for screening and ranking sequestration targets. Relative permeability curves measured on samples from seven potential storage formations are used to illustrate the effect on the CoPs. In the case of a constant pressure boundary and constant rate injection scenario, the CoP for small overpressures is time-invariant and independent of relative permeability. Depending on the relative values of overall mobilities of two-phase region and of brine region, the risk due to a critical CoP which lies in the two-phase region can either increase or decrease with time. In contrast, the risk due to a CoP in the drying region always decreases with time. The assumption of constant pressure boundaries is optimistic in the sense that CoPs extend the least distance from the injection well. We extend the analytical model to infinite-acting aquifers to get a more widely applicable estimate of risk. An analytical expression for pressure profile is developed by adapting water influx models from traditional reservoir engineering to the "three-region" saturation distribution. For infinite-acting boundary condition, the CoP trends depend on same factors as in the constant pressure case, and also depend upon the rate of change of aquifer boundary pressure with time. Commercial reservoir simulators are used to verify the analytical model for the constant pressure boundary condition. The CoP trends from the analytical solution and simulation results show a good match. To achieve safe and secure CO₂ storage in underground reservoirs several state and national government agencies are working to develop regulatory frameworks to estimate various risks associated with CO₂ injection in saline aquifers. Certification Framework (CF), developed by Oldenburg et al (2007) is a similar kind of regulatory approach to certify the safety and effectiveness of geologic carbon sequestration sites. CF is a simple risk assessment approach for evaluating CO₂ and brine leakage risk associated only with subsurface processes and excludes compression, transportation, and injection-well leakage risk. Certification framework is applied to several reservoirs in different geologic settings. These include In Salah CO₂ storage project Krechba, Algeria, Aquistore CO₂ storage project Saskatchewan, Canada and WESTCARB CO₂ storage project, Solano County, California. Compositional reservoir simulations in CMG-GEM are performed for CO₂ injection in each storage reservoir to predict pressure build up risk and CO₂ leakage risk. CO₂ leakage risk is also estimated using the catalog of pre-computed reservoir simulation results. Post combustion CO₂ capture is required to restrict the continuous increase of carbon content in the atmosphere. Coal fired electricity generating stations are the dominant players contributing to the continuous emissions of CO₂ into the atmosphere. U.S. government has planned to install post combustion CO₂ capture facility in many coal fired power plants including W.A. Parish electricity generating station in south Texas. Installing a CO₂ capture facility in a coal fired power plant increases the capital cost of installation and operating cost to regenerate the turbine solvent (steam or natural gas) to maintain the stripper power requirement. If a coal-fired power plant with CO₂ capture is situated over a viable source for geothermal heat, it may be desirable to use this heat source in the stripper. Geothermal brine can be used to replace steam or natural gas which in turn reduces the operating cost of the CO₂ capture facility. High temperature brine can be produced from the underground geothermal brine reservoir and can be injected back to the reservoir after the heat from the hot brine is extracted. This will maintain the reservoir pressure and provide a long-term supply of hot brine to the stripper. Simulations were performed to supply CO₂ capture facility equivalent to 60 MWe electric unit to capture 90% of the incoming CO₂ in WA Parish electricity generating station. A reservoir simulation study in CMG-GEM is performed to evaluate the feasibility to recycle the required geothermal brine for 30 years time. This pilot study is scaled up to 15 times of the original capacity to generate 900 MWe stripping system to capture CO₂ at surface. / text

Après des décennies de développement, l'ablation laser est devenue une technique importante pour un grand nombre d'applications telles que le dépôt de couches minces, la synthèse de nanoparticules, le micro-usinage, l’analyse chimique, etc. Des études expérimentales ainsi que théoriques ont été menées pour comprendre les mécanismes physiques fondamentaux mis en jeu pendant l'ablation et pour déterminer l’effet de la longueur d'onde, de la durée d'impulsion, de la nature de gaz ambiant et du matériau de la cible. La présente thèse décrit et examine l'importance relative des mécanismes physiques qui influencent les caractéristiques des plasmas d’aluminium induits par laser. Le cadre général de cette recherche forme une étude approfondie de l'interaction entre la dynamique de la plume-plasma et l’atmosphère gazeuse dans laquelle elle se développe. Ceci a été réalisé par imagerie résolue temporellement et spatialement de la plume du plasma en termes d'intensité spectrale, de densité électronique et de température d'excitation dans différentes atmosphères de gaz inertes tel que l’Ar et l’He et réactifs tel que le N2 et ce à des pressions s’étendant de 10‾7 Torr (vide) jusqu’à 760 Torr (pression atmosphérique). Nos résultats montrent que l'intensité d'émission de plasma dépend généralement de la nature de gaz et qu’elle est fortement affectée par sa pression. En outre, pour un délai temporel donné par rapport à l'impulsion laser, la densité électronique ainsi que la température augmentent avec la pression de gaz, ce qui peut être attribué au confinement inertiel du plasma. De plus, on observe que la densité électronique est maximale à proximité de la surface de la cible où le laser est focalisé et qu’elle diminue en s’éloignant (axialement et radialement) de cette position. Malgré la variation axiale importante de la température le long du plasma, on trouve que sa variation radiale est négligeable. La densité électronique et la température ont été trouvées maximales lorsque le gaz est de l’argon et minimales pour l’hélium, tandis que les valeurs sont intermédiaires dans le cas de l’azote. Ceci tient surtout aux propriétés physiques et chimiques du gaz telles que la masse des espèces, leur énergie d'excitation et d'ionisation, la conductivité thermique et la réactivité chimique. L'expansion de la plume du plasma a été étudiée par imagerie résolue spatio-temporellement. Les résultats montrent que la nature de gaz n’affecte pas la dynamique de la plume pour des pressions inférieures à 20 Torr et pour un délai temporel inférieur à 200 ns. Cependant, pour des pressions supérieures à 20 Torr, l'effet de la nature du gaz devient important et la plume la plus courte est obtenue lorsque la masse des espèces du gaz est élevée et lorsque sa conductivité thermique est relativement faible. Ces résultats sont confirmés par la mesure de temps de vol de l’ion Al+ émettant à 281,6 nm. D’autre part, on trouve que la vitesse de propagation des ions d’aluminium est bien définie juste après l’ablation et près de la surface de la cible. Toutefois, pour un délai temporel important, les ions, en traversant la plume, se thermalisent grâce aux collisions avec les espèces du plasma et du gaz. / After decades of development, laser ablation has become an important technique for a large number of applications such as thin film deposition, nanoparticle synthesis, micromachining, chemical analysis, etc. Experimental and theoretical studies have been conducted to understand the physical mechanisms of the laser ablation processes and their dependence on the laser wavelength, pulse duration, ambient gas and target material. The present dissertation describes and investigates the relative importance of the physical mechanisms influencing the characteristics of aluminum laser-induced plasmas. The general scope of this research encompasses a thorough study of the interplay between the plasma plume dynamics and the ambient gas in which they expand. This is achieved by imaging and analyzing the temporal and spatial evolution the plume in terms of spectral intensity, electron density and excitation temperature within various environments extending from vacuum (10‾7 Torr) to atmospheric pressure (760 Torr), in an inert gas like Ar and He, as well as in a chemically active gas like N2. Our results show that the plasma emission intensity generally differs with the nature of the ambient gas and it is strongly affected by its pressure. In addition, for a given time delay after the laser pulse, both electron density and plasma temperature increase with the ambient gas pressure, which is attributed to plasma confinement. Moreover, the highest electron density is observed close to the target surface, where the laser is focused and it decreases by moving away (radially and axially) from this position. In contrast with the significant axial variation of plasma temperature, there is no large variation in the radial direction. Furthermore, argon was found to produce the highest plasma density and temperature, and helium the lowest, while nitrogen yields intermediate values. This is mainly due to their physical and chemical properties such as the mass, the excitation and ionization levels, the thermal conductivity and the chemical reactivity. The expansion of the plasma plume is studied by time- and space-resolved imaging. The results show that the ambient gas does not appreciably affect plume dynamics as long as the gas pressure remains below 20 Torr and the time delay below 200 ns. However, for pressures higher than 20 Torr, the effect of the ambient gas becomes important and the shorter plasma plume length corresponds to the highest gas mass species and the lowest thermal conductivity. These results are confirmed by Time-Of-Flight (TOF) measurements of Al+ line emitted at 281.6 nm. Moreover, the velocity of aluminum ions is well defined at the earliest time and close to the target surface. However, at later times, the ions travel through the plume and become thermalized through collisions with plasma species and with surrounding ambient gas.