Successful management of hydrocarbon reservoirs, geothermal energy extraction sites, radioactive waste and CO2 storage sites depends on a detailed knowledge of fluid transport properties, porosity and permeability. Amongst deformation processes, fluid-rock interaction plays an important role in controlling the petrophysical properties of a rock. The presence of fluids in the rocks induce chemical and physical changes in compositions and texture, affecting porosity and permeability, hence influencing dynamic transport properties and fluid flow. Fluid-rock interaction processes have been deeply investigated in nature and in numerous experimental and numerical modelling studies. However, these studies lack a spatio-temporal characterization of the dynamic evolution of porosity and reaction microfabrics. There is no clear understanding of the spatio-temporal evolution of these properties in three dimensions, and how this evolution affects fluid percolation in the rock. Computed X-ray micro-Tomography (μCT) was applied to investigate these processes in three dimensions and observe their evolution in time (4DμCT). The combination of μCT with 2D analytical techniques (e.g. scanning electron microscope, SEM, electron microcrobe, EMPA, electron backscatter diffraction, EBSD) furthermore enables the extrapolation of the information gained from 2D analyses to the 3rd an 4th dimension (4D μCT). The thesis investigates two different categories of fluid-rock interaction processes, by using 4DμCT to monitor the evolution of mineral reactions (in the first case) and porosity (second case) in relation to strain and time. In the first case study, natural rock samples were analysed. The samples show a compositional change along a strain gradient from olivinic metagabbros to omphacite-garnet bearing eclogites in a ductile shear zone. Synchroton-based x-ray microtomography (sμCT) was applied to document the 3D evolution of garnets along the strain gradient (which represent the 4th dimension). The 3D spatial arrangement of garnet microfabrics can help determine the deformation history and the extent of fluid-rock interaction active during deformation. Results from the sμCT show that in the low strain domain, garnets form a large and well interconnected cluster that develops throughout the entire sample and garnet coronas never completely encapsulate olivine grains. In the most highly deformed eclogites, the oblate shapes of garnets reflect a deformational origin of the microfabrics. EBSD analyses reveal that garnets do not show evidence for crystal plasticity, but rather they highlight evidence for minor fracturing, neo-nucleation and overgrowth, which points to a mechanical disintegration of the garnet coronas during strain localisation. In the second case study, pressure-solution processes were investigated using NaCl as rock-analogue, to monitor the evolution of porosity and pore connectivity in four dimensions, providing a time-resolved characterization of the processes. NaCl samples were uniaxially compacted and μCT scans were taken at regular interval times to characterize the evolution of grain morphologies, pore space and macro-connectivity of the samples. Different uniaxial loads, as well as different bulk sample compositions (phyllosilicates and/or glass beads) were used to investigate their effect on the process. Greater uniaxial loads, and the presence of phyllosilicates within the deforming NaCl columns were found to enhance pressure-solution processes. The pore space becomes highly disconnected in the presence of phyllosilicates, with important implications for fluid percolation and dynamic transport properties. Mean strain rates, calculated from volumetric Digital Image Correlation (3D-DIC) analyses, were found to be higher where phyllosilicates were located. The combination of μCT with volumetric DIC and SEM imaging proved to be an efficient analytical method for investigating the dynamic behaviour of porosity and permeability during ongoing pressure-solution processes. The results showed that fluid-rock interaction critically modifies the rocks at the pore/grain scale, with important consequences on dynamic fluid transport properties. The combination of μCT with classical 2D techniques provided a better understanding on the dynamic evolution of transport properties and fluid percolation during fluid-rock interaction processes, allowing the characterization in three dimensions of reaction microfabrics and porosity.

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Carbonate rocks are of global importance as they contain about 50% of the world’s remaining hydrocarbon reserves and are also a major host to the world’s groundwater resources. Therefore, understanding and modelling the fluid flow processes in carbonates are of great importance. A critical problem is that, unlike homogenous media (such as sandstones), carbonates often show features, including porosity, that span across a wide spatial range, from sub-micron porosity to fractures of meters length-scale. In this study X-ray computed micro-tomography (μCT) has been utilised as a tool to monitor two phase (oil-brine) flow in porous carbonate (dolomite) plugs at ambient temperature and pressures smaller than 690 kPa. A simple, low-cost and highly X-ray transparent core-holder was utilised for which the design is introduced. Capillary end effects were recognised and avoided in data analysis. Displacement processes that occur in the dolomite under water-wet, oil-wet, and partially mixed-wet states were investigated. The experiments consisted of a series of drainage and imbibition processes occurring under capillary and viscous dominated flow regimes. Pore-scale mechanisms of piston-like displacement and snap-off (or at least clear results of them), that were previously observed in sandstones and 2D micro-models, were observed in the dolomite under study. In addition, a new pore-scale mechanism was identified which occurred at high capillary numbers, referred to as droplet-fragmentation. This new pore-scale mechanism may provide an explanation to the capillary-desaturation process for heterogeneous media. In the experiments performed on the oil-wet plug formation of a stable water in oil emulsion was observed which appears to be the first 3D observation of in situ emulsion formation made using μCT. Direct visualisation of the oil-brine-rock configurations and measurement of the contact angles are presented. A comparison was made for the contact angle distributions measured for the water-wet and oil-wet conditions. Observation of fluid displacement processes as well as oil-brine-rock contact angle distributions demonstrate that pore-scale imaging provides a promising tool for wettability characterisation on both pore and core scales. Such detailed wettability data can also be used in pore-scale flow models. For the dolomite under study multiple-scale pore network models were constructed by integrating single-scale networks extracted from μCT images acquired at different length-scales. Mercury injection capillary pressure laboratory measurements were used to evaluate the capillary pressure (vs. saturation) curves calculated using single, two-scale, and three-scale network models of this dolomite. The integrated networks displayed an improved match to the laboratory measurements in comparison with the single-scale network model. The three-scale network provided the closest simulated curve, this result confirms that a more representative model displays closer properties. While simulated capillary pressure curves are close (converging) for the integrated networks the calculated relative permeability curves show variability for different multiple-scale networks. The present work demonstrates that the pore-scale fluid displacement processes occurring in heterogeneous porous media are more complex than those occurring in homogeneous media. In addition, successful fluid flow simulations require construction of multiple-scale models as well as consideration of the pore-scale processes (such as droplet-fragmentation) that are specific to such complex pore systems.

The occurrence of hot tearing during solidification is one of the major factors influencing both the quality and productivity of aluminum castings. In order to reduce the formation of hot tears, quantitative information regarding both hot tearing formation and semi-solid deformation is essential. In this study, the mechanisms of hot tearing and semi-solid deformation have been investigated via two novel techniques: x-ray micro-tomography on material deformed in the semi-solid region, and development of a three phase microstructural model based on a geometry derived from a Voronoi diagram with rounded corners and porosity. Numerical techniques were utilized to quantify both the size evolution and orientation of internal damage relative to void growth. In order to conduct the above research, a new semi-solid tensile deformation methodology was devised which uses a two thermocouple control technique to enable accurate measurement of semi-solid tensile strength and ductility. The experimental work was conducted on the aluminum – magnesium alloy AA5182 in the as-cast and hot isostatic pressing (HIP) states. The x-ray micro-tomography technique was used to observe that semi-solid deformation is accommodated by internal damage via growth of as-cast porosity and the nucleation of new damage-based voids. As the volume fraction of damage increases, the growth of voids occurs in an orientation perpendicular to the loading direction, both through expansion within the grain boundary liquid and via coalescence between voids. The damage then localizes, causing failure. The finite element semi-solid microstructural model was used to explore the effects of fraction solid, fraction porosity, and grain size on semi-solid constitutive behaviour. The simulations revealed that increased grain size and fraction porosity lead to a reduction in flow stress for a given fraction solid. Furthermore, local strain accumulation was linked to hot tearing, since strain localizes in the liquid very early in the deformation process. Based on the model predictions, a new constitutive relationship was developed over the range 0.75 < fs < 0.95. Together, these two techniques have provided powerful new insight, such as the critical role played by as-cast porosity, on the phenomena of hot tearing and semi-solid deformation in aluminum alloys.

The occurrence of hot tearing during solidification is one of the major factors influencing both the quality and productivity of aluminum castings. In order to reduce the formation of hot tears, quantitative information regarding both hot tearing formation and semi-solid deformation is essential. In this study, the mechanisms of hot tearing and semi-solid deformation have been investigated via two novel techniques: x-ray micro-tomography on material deformed in the semi-solid region, and development of a three phase microstructural model based on a geometry derived from a Voronoi diagram with rounded corners and porosity. Numerical techniques were utilized to quantify both the size evolution and orientation of internal damage relative to void growth. In order to conduct the above research, a new semi-solid tensile deformation methodology was devised which uses a two thermocouple control technique to enable accurate measurement of semi-solid tensile strength and ductility. The experimental work was conducted on the aluminum – magnesium alloy AA5182 in the as-cast and hot isostatic pressing (HIP) states. The x-ray micro-tomography technique was used to observe that semi-solid deformation is accommodated by internal damage via growth of as-cast porosity and the nucleation of new damage-based voids. As the volume fraction of damage increases, the growth of voids occurs in an orientation perpendicular to the loading direction, both through expansion within the grain boundary liquid and via coalescence between voids. The damage then localizes, causing failure. The finite element semi-solid microstructural model was used to explore the effects of fraction solid, fraction porosity, and grain size on semi-solid constitutive behaviour. The simulations revealed that increased grain size and fraction porosity lead to a reduction in flow stress for a given fraction solid. Furthermore, local strain accumulation was linked to hot tearing, since strain localizes in the liquid very early in the deformation process. Based on the model predictions, a new constitutive relationship was developed over the range 0.75 < fs < 0.95. Together, these two techniques have provided powerful new insight, such as the critical role played by as-cast porosity, on the phenomena of hot tearing and semi-solid deformation in aluminum alloys.

The degree of mineral liberation is important for the efficiency of subsequent physical separation processes such as froth flotation. Mineral liberation studies involve determining the volumetric abundance or volumetric grade distribution of a specific mineralogical phase in a particular mineral. Currently, methodologies for assessing mineral liberation are laborious regarding sample preparation, analysis time (from weeks to months), and the need for stereological correction. These constraints can be eliminated by using X-ray CT which gives the cross-sections directly from three-dimensional data in shorter time (from ten minutes to hours) with minimal sample preparation. X-ray computed tomography (CT) is a non-destructive technique which allows three-dimensional visualisation of inner structures of an object based on the variations in density and atomic composition. Initially, it was developed as a medical tool for imaging soft tissue and bone. During the last decade, the number of X-ray CT applications in engineering and geology has steadily increased, with the improvements in performance and imaging capabilities. The aim of the present work is to apply X-ray CT technique for finely divided ore samples and to study the relationship between mineral liberation and CT results. Four different ore types were used in this study: Northparkes ore (Australia), Ernest Henry ore (Australia), Keetac ore (USA) and Cannington ore (Australia). Different settings of the desktop X-ray CT technique were applied for each particular ore sample for several ore liberation (particle size distribution) properties. Two dimensional CT images were reconstructed from the three-dimensional X-ray CT data. It was found that the settings for CT technique were a function of the ore type. Particularly in the case of Cannington (high density ore) the best setting conditions split from the rest of the ores tested. The appearance of different artifacts occurring during the analysis were studied and kept to the minimum. A functionality between mineral liberation and CT results was found. The variables affecting the most the results were the Voltage and Minimum Intensity Percentage. Contrary to the expected trends, variables having a negligible effect on the results were found to be exposure time / equivalent Al filter thickness.

The degree of mineral liberation is important for the efficiency of subsequent physical separation processes such as froth flotation. Mineral liberation studies involve determining the volumetric abundance or volumetric grade distribution of a specific mineralogical phase in a particular mineral. Currently, methodologies for assessing mineral liberation are laborious regarding sample preparation, analysis time (from weeks to months), and the need for stereological correction. These constraints can be eliminated by using X-ray CT which gives the cross-sections directly from three-dimensional data in shorter time (from ten minutes to hours) with minimal sample preparation. X-ray computed tomography (CT) is a non-destructive technique which allows three-dimensional visualisation of inner structures of an object based on the variations in density and atomic composition. Initially, it was developed as a medical tool for imaging soft tissue and bone. During the last decade, the number of X-ray CT applications in engineering and geology has steadily increased, with the improvements in performance and imaging capabilities. The aim of the present work is to apply X-ray CT technique for finely divided ore samples and to study the relationship between mineral liberation and CT results. Four different ore types were used in this study: Northparkes ore (Australia), Ernest Henry ore (Australia), Keetac ore (USA) and Cannington ore (Australia). Different settings of the desktop X-ray CT technique were applied for each particular ore sample for several ore liberation (particle size distribution) properties. Two dimensional CT images were reconstructed from the three-dimensional X-ray CT data. It was found that the settings for CT technique were a function of the ore type. Particularly in the case of Cannington (high density ore) the best setting conditions split from the rest of the ores tested. The appearance of different artifacts occurring during the analysis were studied and kept to the minimum. A functionality between mineral liberation and CT results was found. The variables affecting the most the results were the Voltage and Minimum Intensity Percentage. Contrary to the expected trends, variables having a negligible effect on the results were found to be exposure time / equivalent Al filter thickness.

The degree of mineral liberation is important for the efficiency of subsequent physical separation processes such as froth flotation. Mineral liberation studies involve determining the volumetric abundance or volumetric grade distribution of a specific mineralogical phase in a particular mineral. Currently, methodologies for assessing mineral liberation are laborious regarding sample preparation, analysis time (from weeks to months), and the need for stereological correction. These constraints can be eliminated by using X-ray CT which gives the cross-sections directly from three-dimensional data in shorter time (from ten minutes to hours) with minimal sample preparation. X-ray computed tomography (CT) is a non-destructive technique which allows three-dimensional visualisation of inner structures of an object based on the variations in density and atomic composition. Initially, it was developed as a medical tool for imaging soft tissue and bone. During the last decade, the number of X-ray CT applications in engineering and geology has steadily increased, with the improvements in performance and imaging capabilities. The aim of the present work is to apply X-ray CT technique for finely divided ore samples and to study the relationship between mineral liberation and CT results. Four different ore types were used in this study: Northparkes ore (Australia), Ernest Henry ore (Australia), Keetac ore (USA) and Cannington ore (Australia). Different settings of the desktop X-ray CT technique were applied for each particular ore sample for several ore liberation (particle size distribution) properties. Two dimensional CT images were reconstructed from the three-dimensional X-ray CT data. It was found that the settings for CT technique were a function of the ore type. Particularly in the case of Cannington (high density ore) the best setting conditions split from the rest of the ores tested. The appearance of different artifacts occurring during the analysis were studied and kept to the minimum. A functionality between mineral liberation and CT results was found. The variables affecting the most the results were the Voltage and Minimum Intensity Percentage. Contrary to the expected trends, variables having a negligible effect on the results were found to be exposure time / equivalent Al filter thickness.

The degree of mineral liberation is important for the efficiency of subsequent physical separation processes such as froth flotation. Mineral liberation studies involve determining the volumetric abundance or volumetric grade distribution of a specific mineralogical phase in a particular mineral. Currently, methodologies for assessing mineral liberation are laborious regarding sample preparation, analysis time (from weeks to months), and the need for stereological correction. These constraints can be eliminated by using X-ray CT which gives the cross-sections directly from three-dimensional data in shorter time (from ten minutes to hours) with minimal sample preparation. X-ray computed tomography (CT) is a non-destructive technique which allows three-dimensional visualisation of inner structures of an object based on the variations in density and atomic composition. Initially, it was developed as a medical tool for imaging soft tissue and bone. During the last decade, the number of X-ray CT applications in engineering and geology has steadily increased, with the improvements in performance and imaging capabilities. The aim of the present work is to apply X-ray CT technique for finely divided ore samples and to study the relationship between mineral liberation and CT results. Four different ore types were used in this study: Northparkes ore (Australia), Ernest Henry ore (Australia), Keetac ore (USA) and Cannington ore (Australia). Different settings of the desktop X-ray CT technique were applied for each particular ore sample for several ore liberation (particle size distribution) properties. Two dimensional CT images were reconstructed from the three-dimensional X-ray CT data. It was found that the settings for CT technique were a function of the ore type. Particularly in the case of Cannington (high density ore) the best setting conditions split from the rest of the ores tested. The appearance of different artifacts occurring during the analysis were studied and kept to the minimum. A functionality between mineral liberation and CT results was found. The variables affecting the most the results were the Voltage and Minimum Intensity Percentage. Contrary to the expected trends, variables having a negligible effect on the results were found to be exposure time / equivalent Al filter thickness.

The degree of mineral liberation is important for the efficiency of subsequent physical separation processes such as froth flotation. Mineral liberation studies involve determining the volumetric abundance or volumetric grade distribution of a specific mineralogical phase in a particular mineral. Currently, methodologies for assessing mineral liberation are laborious regarding sample preparation, analysis time (from weeks to months), and the need for stereological correction. These constraints can be eliminated by using X-ray CT which gives the cross-sections directly from three-dimensional data in shorter time (from ten minutes to hours) with minimal sample preparation. X-ray computed tomography (CT) is a non-destructive technique which allows three-dimensional visualisation of inner structures of an object based on the variations in density and atomic composition. Initially, it was developed as a medical tool for imaging soft tissue and bone. During the last decade, the number of X-ray CT applications in engineering and geology has steadily increased, with the improvements in performance and imaging capabilities. The aim of the present work is to apply X-ray CT technique for finely divided ore samples and to study the relationship between mineral liberation and CT results. Four different ore types were used in this study: Northparkes ore (Australia), Ernest Henry ore (Australia), Keetac ore (USA) and Cannington ore (Australia). Different settings of the desktop X-ray CT technique were applied for each particular ore sample for several ore liberation (particle size distribution) properties. Two dimensional CT images were reconstructed from the three-dimensional X-ray CT data. It was found that the settings for CT technique were a function of the ore type. Particularly in the case of Cannington (high density ore) the best setting conditions split from the rest of the ores tested. The appearance of different artifacts occurring during the analysis were studied and kept to the minimum. A functionality between mineral liberation and CT results was found. The variables affecting the most the results were the Voltage and Minimum Intensity Percentage. Contrary to the expected trends, variables having a negligible effect on the results were found to be exposure time / equivalent Al filter thickness.