Colloidal transport and clogging in porous media is a phenomenon of critical importance in many b... more Colloidal transport and clogging in porous media is a phenomenon of critical importance in many branches of applied sciences and engineering. It involves multiple types of interactions that span from the sub-colloid scale (electrochemical interactions) up to the porescale (bridging), thus challenging the development of representative modelling. So far published simulation results of colloidal or particulate transport are based on either reduced set of forces or spatial dimensions. Here we present an approach enabling to overcome both computational and physical limitations posed by a problem of 3D colloidal transport in porous media. An adaptive octree mesh is introduced to a coupled CFD and DEM method while enabling tracking of individual colloids. Flow fields are calculated at a coarser scale throughout the domain, and at fine-scale around colloids. The approach accounts for all major interactions in such a system: elastic, electrostatic, and hydrodynamic forces acting between colloids, as well as colloids and the collector surface. The method is demonstrated for a single throat model made of four spherical segments, and the impact of clogging is reported in terms of the evolution of the critical path diameter for percolation and permeability. We identified four stages of clogging development depending on position and time of individual colloid entrapment, which in turn correlates to a cluster evolution and local transport.
NMR transverse relaxation responses in porous media provide a sensitive probe of the micro-struct... more NMR transverse relaxation responses in porous media provide a sensitive probe of the micro-structure yet are influenced by a set of factors which are not easily detangled. Low-field T2 transverse relaxation measurements can be carried out quickly and are frequently used to derive pore size distributions and determine derivate parameters like movable fluid volumes or permeability. Here we present an inverse solution workflow extracting related intrinsic physical parameters of the system by tightly fitting experiment and numerical simulation(s). We propose a Bayesian optimization approach that determines five T2 related properties associated with two values of temperature simultaneously. This concurrent optimization (CO-OPT) utilizes Gaussian process regression to determine the intrinsic physical parameters leading to a match to experiment with a minimal number of function evaluations. A multi-modal search strategy is employed to identify non-unique solution sets of the problem. The workflow is demonstrated on Bentheimer sandstone, identifying five intrinsic physical parameters simultaneously, namely the surface relaxivity of quartz and the effective diffusion and relaxation times of the clay regions at 20 ∘ C and 60 ∘ C, providing the temperature-dependent quartz surface relaxivity and effective clay parameters. Given the generality of the method, it can easily be adapted to transverse relaxation experiments, or dynamic conditions where e.g., a change in wettability is monitored by intrinsic NMR parameters.
Continual application of nitrogen (N), phosphorous (P) and potassium (K) fertilizer may not retur... more Continual application of nitrogen (N), phosphorous (P) and potassium (K) fertilizer may not return a profit to farmers due to the costs of application and the loss of NPK from soil in various ways. Thus, a combination of NPK granule with a porous biochar (termed here as BNPK) appears to offer multiple benefits resulting from the excellent properties of biochar. Given the lack of information on the properties of NPK and BNPK fertilizers, it is necessary to investigate the characteristics of both to achieve a good understanding of why BNPK granule is superior to NPK granule. Therefore, this study aims to investigate the characteristics of a maize straw biochar mixed with NPK granule, before and after application to soil, and compare them to those for a commercial NPK granule. The BNPK granule, with a greater surface area and porosity, showed a higher capacity to store and donate electrons than the NPK granule. Relatively lower concentrations of Ca, P, K, Si and Mg were dissolved from the BNPK, indicating the ability of the BNPK granule to maintain these mineral elements and reduce dissolution rate. To study the nutrient storage mechanism of the BNPK granule in the soil, short- and long-term leaching experiments were conducted. During the experiments, organo-mineral clusters, comprising C, P, K, Si, Al and Fe, were formed on the surface and inside the biochar pores. However, BNPK was not effective in reducing N leaching, in the absence of plants, in a red chromosol soil.
the pixels correspond to the density and composition of the material imaged. Hence, in monominera... more the pixels correspond to the density and composition of the material imaged. Hence, in monomineralic rock, such as the samples studied in this paper, micro-CT images are 3D porosity maps.
This paper presents comparisons for resistivity index and capillary pressure between laboratory m... more This paper presents comparisons for resistivity index and capillary pressure between laboratory measurements on conventional core plugs and predictions of the image-based techniques and network modelling. The laboratory measurements were carried out using a combined, 4-electrode Pc/RI apparatus based on the porous plate technique. A simple 2wt% NaCl brine-air system was used in the experiments. The porous systems investigated include a carbonate core from a Middle Eastern reservoir, an outcrop limestone (Mt Gambier) and outcrop sandstone (Fontainebleau). The predictions of porosity, permeability, formation factor, capillary pressure and resistivity index were made using the image-based techniques and network models. The validity of the predictions was then compared with the laboratory data. The comparisons show that both predictive tools have a good agreement with the laboratory data for porosity and formation factor while overestimate the laboratory permeability. The results demonstrate that, above a water saturation of 30%, both laboratory measurements and predictions follow the Archie behaviour. Below 30%, however, a "non-Archie" behavior is generally observed. The image based calculations and laboratory measurements are generally close to each other for the outcrop samples whereas the network model shows slightly different results for the reservoir carbonate. The pore entry radii calculated using the image-based technique and network models show similar results only for the outcrop sandstone. The reasons for the poor estimations are assumed to be due to poor image quality or insufficient resolution for feature imaging and sample size or scale dependence.
Recent progress in the development of X-ray micro-computed tomography (μ-CT) makes it possible to... more Recent progress in the development of X-ray micro-computed tomography (μ-CT) makes it possible to directly visualize and quantify various features of the microstructure of complex porous media including sedimentary rocks, in particular [1-5]. In various porous media processes such as chemical dissolution and mechanical compaction, the conditions may be appropriate to allow local particle detachment and displacement within the porous medium. It is noted that for flow-throughporous-media experiments, a lack of observation of fines production does not preclude considerable local mobilization of particles within the porous medium at the pore-scale. Particle mobilization may be triggered by inertial forces of flow itself or releasing by chemical reactions or other forces and then displacing by flow. The local mobilization of fines is a largely unexplored phenomenon at the pore scale due to difficulty in direct access to local particle displacement.
Rapid advances in additive manufacturing have kindled widespread interest in the rational design ... more Rapid advances in additive manufacturing have kindled widespread interest in the rational design of metamaterials with unique properties over the past decade. However, many applications require multi‐physics metamaterials, where multiple properties are simultaneously optimized. This is challenging since different properties, such as mechanical and mass transport properties, typically impose competing requirements on the nano‐/micro‐/meso‐architecture of metamaterials. Here, a parametric metamaterial design strategy that enables independent tuning of the effective permeability and elastic properties is proposed. Hyperbolic tiling theory is applied to devise simple templates, based on which triply periodic minimal surfaces (TPMS) are partitioned into hard and soft regions. Through computational analyses, it is demonstrated how the decoration of hard, soft, and void phases within the TPMS substantially enhances their permeability–elasticity property space and offers high tunability in ...
Resistivity measurements are a major input into hydrocarbon reserve estimation and are usually de... more Resistivity measurements are a major input into hydrocarbon reserve estimation and are usually described by Archie's laws. In this study digital rock physics (DRP) is utilized to analyse the mechanisms of non-Archie and Archie behaviour of formation factor (FF) and resistivity index (RI) of low porosity Fontainebleau sandstone for ambient conditions and under high confining pressure, respectively. Fontainebleau sandstone was imaged by micro-CT at a resolution of one micron and sub-resolution details of grain contact width distribution along with their length, extracted from a set of scanning electron microscope (SEM) images. The nano-scale aperture of grain contacts, which is below image resolution, is accounted for in micro-CT based numerical calculations by assigning effective porosity and conductivity to individual voxels of the extracted grain contact network. A porosity reduction of grain contacts and open pore space as function of applied confining pressure is introduced, ...
Wettability is a key factor defining ultimate hydrocarbon recovery. Extensive experimentation is ... more Wettability is a key factor defining ultimate hydrocarbon recovery. Extensive experimentation is required to replicate the wetting state of reservoir rocks. This involves a rock sample wettability restoration procedure, including an aging step and a concept of an optimum aging time, in which asphaltene chemistry plays a major role. There are numerous reports on significance of various crude oil components and elements of asphaltene structure to their tendency to interact with the solid phase, though subject evidence is contradictory. We investigate a possible relationship between the composition of oil, kinetics of an aging process, and a change of sandstone rock wettability. Wettability state of the cores was monitored using low-field NMR relaxometry. The composition and key components of accumulated deposits were established by matching 1H solution-state NMR and X-band EPR spectra of deposits to the spectra of SARA (saturates-aromatics-resins-asphaltenes) fractions of aging fluids. We determined adsorpt...
Numerical flow simulation in shale, especially in the nanoscale porous system of a shale matrix, ... more Numerical flow simulation in shale, especially in the nanoscale porous system of a shale matrix, is still challenging because no imaging device can effectively describe the nanoscale porous structure of shale to satisfy both resolution and field of view (FOV). The resolution of an X-ray computed tomography (µ-CT) image is too low to detect the nanoscale features of porous structure in shale. The FOV of a focused ion beam scanning electron microcopy (FIB-SEM) image, on the other hand, is too small to capture the heterogeneity of a shale matrix. Therefore, we propose a semi-quantitative, Multiscale reconstruction strategy to build an image based network model of a shale sample with nanoscale resolution covering three orders of magnitude of FIB-SEM image volume. In this study, shale is considered a Multiscale porous media consisting of microscale and nanoscale structures. The microscale structures reflect the morphological features of organic matter, clay minerals, intergranular pores and micro-cracks that can be detected by µ-CT. The nanoscale features focus on the inner porous structure of organic matter and clay minerals that can be characterised using a scanning electron microcopy (SEM) or a FIB-SEM. nanoscale. Multiscale means reconstruction work that is carried out at the microscale and nanoscale separately, using the multiple-point statistics (MPS) method. Microscale reconstruction aims to recover the connections that are undetected among microscale objects due to the low resolution of the µ-CT image. Within the organic and clay phases, a nanoscale reconstruction is then carried out to model the nanoscale porous structure. Semi-quantitative means the segmented µ-CT image is used as conditional data in microscale reconstruction to maintain the reality of microscale structures. To relieve the heavy burden of data storage, a network modelling procedure is simultaneously undertaken alongside nanoscale reconstruction to transfer the reconstructed structure to a network model. Based on the established network model, flow simulation is undertaken by applying an extended Beskok-Karniadakis (B-K) model considering continuum, non-continuum and surface diffusion. The results show that the permeability ratio is affected by pressure, the molecule diameter of gas and surface diffusion.
Development of microneedles for unskilled and painless collection of blood or drug delivery addre... more Development of microneedles for unskilled and painless collection of blood or drug delivery addresses the quality of healthcare through early intervention at point-of-care. Microneedles with submicron to millimeter features have been fabricated from materials such as metals, silicon, and polymers by subtractive machining or etching. However, to date, large-scale manufacture of hollow microneedles has been limited by the cost and complexity of microfabrication techniques. This paper reports a novel manufacturing method that may overcome the complexity of hollow microneedle fabrication. Prototype microneedles with open microfluidic channels are fabricated by laser stereolithography. Thermoplastic replicas are manufactured from these templates by soft-embossing with high fidelity at submicron resolution. The manufacturing advantages are (a) direct printing from computer-aided design (CAD) drawing without the constraints imposed by subtractive machining or etching processes, (b) high-fi...
Clay‐rich deposits are commonly assumed to be aquitards which act as natural hydraulic barriers d... more Clay‐rich deposits are commonly assumed to be aquitards which act as natural hydraulic barriers due to their low hydraulic connectivity. Postdepositional weathering processes are known to increase the permeability of aquitards in the near surface but not impact on deeper parts of relatively thick formations. However, syndepositional processes affecting the hydraulic properties of aquitards have previously received little attention in the literature. Here, we analyze a 31 m deep sediment core recovered from an inland clay‐rich sedimentary sequence using a combination of techniques including particle size distribution and microscopy, centrifuge dye tracer testing and micro X‐ray CT imaging. Subaerial deposition of soils within these fine grained alluvial deposits has led to the preservation of considerable macropores (root channels or animal burrows). Connected pores and macropores thus account for vertical hydraulic conductivity (K) of m/s (geometric mean of 13 samples) throughout th...
Physica A: Statistical Mechanics and its Applications, 2018
Abstract X-ray computed tomography ( μ -CT) is considered to be the most effective way to obtain ... more Abstract X-ray computed tomography ( μ -CT) is considered to be the most effective way to obtain the inner structure of rock sample without destructions. However, its limited resolution hampers its ability to probe sub-micro structures which is critical for flow transportation of rock sample. In this study, we propose an innovative methodology to improve the resolution of μ -CT image using neighbour embedding algorithm where low frequency information is provided by μ -CT image itself while high frequency information is supplemented by high resolution scanning electron microscopy (SEM) image. In order to obtain prior for reconstruction, a large number of image patch pairs contain high- and low- image patches are extracted from the Gaussian image pyramid generated by SEM image. These image patch pairs contain abundant information about tomographic evolution of local porous structures under different resolution spaces. Relying on the assumption of self-similarity of porous structure, this prior information can be used to supervise the reconstruction of high resolution μ -CT image effectively. The experimental results show that the proposed method is able to achieve the state-of-the-art performance.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights High-and low-salinity brine was injected into a Berea sandstone core plug Micro-CT images of the core plug was taken before and after injection SEM-EDS analysis showed clay fines production Laboratory measurements showed an 80% decrease in permeability Image analysis show clay straining near the production end of the core plug
An elementary question in porous media research is in regard to the relationship between structur... more An elementary question in porous media research is in regard to the relationship between structure and function. In most fields, the porosity and permeability of porous media are properties of key interest. There is, however, no universal relationship between porosity and permeability since not only does the fraction of void space matter for permeability but also the connectivity of the void fraction. With the evolution of modern day X-ray microcomputed tomography (micro-CT) and advanced computing, it is now possible to visualize porous media at an unprecedented level of detail. Approaches in analyzing micro-CT data of porous structures vary in the literature from phenomenological characterization to network analysis to geometrical and/or topological measurements. This leads to a question about how to consistently characterize porous media in a way that facilitates theoretical developments. In this effort, the Minkowski functionals (MF) emerge from the field of statistical physics where it is evident that many physical processes depend on the geometry and topology of bodies or multiple bodies in 3D space. Herein we review the theoretical basis of the MF, mathematical theorems and methods necessary for porous media characterization, common measurement errors when using micro-CT data and recent findings relating the MF to macroscale porous media properties. This paper is written to provide the basics necessary for porous media characterization and theoretical developments. With the wealth of information generated from 3D imaging of porous media, it is necessary to develop an understanding of the limitations and opportunities in this exciting area of research.
The characterisation of heterogeneous porous media at multiple length scales typically requires t... more The characterisation of heterogeneous porous media at multiple length scales typically requires the classification of structure at some scale to allow the calculation of effective transport properties at a scale relevant for macroscopic description. While such a classification may be derived from various imaging methods, a shortcoming is often the simultaneous characterisation of the connectivity between regions representing different micro-structure. In this work we combine NMR based flow propagators with the simulations performed on corresponding reconstructed structure, and relate the NMR measurements to their simulated global and local representations to study fluid transport locally and the exchange between micro- and macro-porous regions. This is achieved by carrying out detailed lattice Boltzmann simulations and random walk method to track the displacements of tracers in each kind of region. Using Euclidean distance maps (EDT) we analyse the fluid invasion to regions of diffe...
Colloidal transport and clogging in porous media is a phenomenon of critical importance in many b... more Colloidal transport and clogging in porous media is a phenomenon of critical importance in many branches of applied sciences and engineering. It involves multiple types of interactions that span from the sub-colloid scale (electrochemical interactions) up to the porescale (bridging), thus challenging the development of representative modelling. So far published simulation results of colloidal or particulate transport are based on either reduced set of forces or spatial dimensions. Here we present an approach enabling to overcome both computational and physical limitations posed by a problem of 3D colloidal transport in porous media. An adaptive octree mesh is introduced to a coupled CFD and DEM method while enabling tracking of individual colloids. Flow fields are calculated at a coarser scale throughout the domain, and at fine-scale around colloids. The approach accounts for all major interactions in such a system: elastic, electrostatic, and hydrodynamic forces acting between colloids, as well as colloids and the collector surface. The method is demonstrated for a single throat model made of four spherical segments, and the impact of clogging is reported in terms of the evolution of the critical path diameter for percolation and permeability. We identified four stages of clogging development depending on position and time of individual colloid entrapment, which in turn correlates to a cluster evolution and local transport.
NMR transverse relaxation responses in porous media provide a sensitive probe of the micro-struct... more NMR transverse relaxation responses in porous media provide a sensitive probe of the micro-structure yet are influenced by a set of factors which are not easily detangled. Low-field T2 transverse relaxation measurements can be carried out quickly and are frequently used to derive pore size distributions and determine derivate parameters like movable fluid volumes or permeability. Here we present an inverse solution workflow extracting related intrinsic physical parameters of the system by tightly fitting experiment and numerical simulation(s). We propose a Bayesian optimization approach that determines five T2 related properties associated with two values of temperature simultaneously. This concurrent optimization (CO-OPT) utilizes Gaussian process regression to determine the intrinsic physical parameters leading to a match to experiment with a minimal number of function evaluations. A multi-modal search strategy is employed to identify non-unique solution sets of the problem. The workflow is demonstrated on Bentheimer sandstone, identifying five intrinsic physical parameters simultaneously, namely the surface relaxivity of quartz and the effective diffusion and relaxation times of the clay regions at 20 ∘ C and 60 ∘ C, providing the temperature-dependent quartz surface relaxivity and effective clay parameters. Given the generality of the method, it can easily be adapted to transverse relaxation experiments, or dynamic conditions where e.g., a change in wettability is monitored by intrinsic NMR parameters.
Continual application of nitrogen (N), phosphorous (P) and potassium (K) fertilizer may not retur... more Continual application of nitrogen (N), phosphorous (P) and potassium (K) fertilizer may not return a profit to farmers due to the costs of application and the loss of NPK from soil in various ways. Thus, a combination of NPK granule with a porous biochar (termed here as BNPK) appears to offer multiple benefits resulting from the excellent properties of biochar. Given the lack of information on the properties of NPK and BNPK fertilizers, it is necessary to investigate the characteristics of both to achieve a good understanding of why BNPK granule is superior to NPK granule. Therefore, this study aims to investigate the characteristics of a maize straw biochar mixed with NPK granule, before and after application to soil, and compare them to those for a commercial NPK granule. The BNPK granule, with a greater surface area and porosity, showed a higher capacity to store and donate electrons than the NPK granule. Relatively lower concentrations of Ca, P, K, Si and Mg were dissolved from the BNPK, indicating the ability of the BNPK granule to maintain these mineral elements and reduce dissolution rate. To study the nutrient storage mechanism of the BNPK granule in the soil, short- and long-term leaching experiments were conducted. During the experiments, organo-mineral clusters, comprising C, P, K, Si, Al and Fe, were formed on the surface and inside the biochar pores. However, BNPK was not effective in reducing N leaching, in the absence of plants, in a red chromosol soil.
the pixels correspond to the density and composition of the material imaged. Hence, in monominera... more the pixels correspond to the density and composition of the material imaged. Hence, in monomineralic rock, such as the samples studied in this paper, micro-CT images are 3D porosity maps.
This paper presents comparisons for resistivity index and capillary pressure between laboratory m... more This paper presents comparisons for resistivity index and capillary pressure between laboratory measurements on conventional core plugs and predictions of the image-based techniques and network modelling. The laboratory measurements were carried out using a combined, 4-electrode Pc/RI apparatus based on the porous plate technique. A simple 2wt% NaCl brine-air system was used in the experiments. The porous systems investigated include a carbonate core from a Middle Eastern reservoir, an outcrop limestone (Mt Gambier) and outcrop sandstone (Fontainebleau). The predictions of porosity, permeability, formation factor, capillary pressure and resistivity index were made using the image-based techniques and network models. The validity of the predictions was then compared with the laboratory data. The comparisons show that both predictive tools have a good agreement with the laboratory data for porosity and formation factor while overestimate the laboratory permeability. The results demonstrate that, above a water saturation of 30%, both laboratory measurements and predictions follow the Archie behaviour. Below 30%, however, a "non-Archie" behavior is generally observed. The image based calculations and laboratory measurements are generally close to each other for the outcrop samples whereas the network model shows slightly different results for the reservoir carbonate. The pore entry radii calculated using the image-based technique and network models show similar results only for the outcrop sandstone. The reasons for the poor estimations are assumed to be due to poor image quality or insufficient resolution for feature imaging and sample size or scale dependence.
Recent progress in the development of X-ray micro-computed tomography (μ-CT) makes it possible to... more Recent progress in the development of X-ray micro-computed tomography (μ-CT) makes it possible to directly visualize and quantify various features of the microstructure of complex porous media including sedimentary rocks, in particular [1-5]. In various porous media processes such as chemical dissolution and mechanical compaction, the conditions may be appropriate to allow local particle detachment and displacement within the porous medium. It is noted that for flow-throughporous-media experiments, a lack of observation of fines production does not preclude considerable local mobilization of particles within the porous medium at the pore-scale. Particle mobilization may be triggered by inertial forces of flow itself or releasing by chemical reactions or other forces and then displacing by flow. The local mobilization of fines is a largely unexplored phenomenon at the pore scale due to difficulty in direct access to local particle displacement.
Rapid advances in additive manufacturing have kindled widespread interest in the rational design ... more Rapid advances in additive manufacturing have kindled widespread interest in the rational design of metamaterials with unique properties over the past decade. However, many applications require multi‐physics metamaterials, where multiple properties are simultaneously optimized. This is challenging since different properties, such as mechanical and mass transport properties, typically impose competing requirements on the nano‐/micro‐/meso‐architecture of metamaterials. Here, a parametric metamaterial design strategy that enables independent tuning of the effective permeability and elastic properties is proposed. Hyperbolic tiling theory is applied to devise simple templates, based on which triply periodic minimal surfaces (TPMS) are partitioned into hard and soft regions. Through computational analyses, it is demonstrated how the decoration of hard, soft, and void phases within the TPMS substantially enhances their permeability–elasticity property space and offers high tunability in ...
Resistivity measurements are a major input into hydrocarbon reserve estimation and are usually de... more Resistivity measurements are a major input into hydrocarbon reserve estimation and are usually described by Archie's laws. In this study digital rock physics (DRP) is utilized to analyse the mechanisms of non-Archie and Archie behaviour of formation factor (FF) and resistivity index (RI) of low porosity Fontainebleau sandstone for ambient conditions and under high confining pressure, respectively. Fontainebleau sandstone was imaged by micro-CT at a resolution of one micron and sub-resolution details of grain contact width distribution along with their length, extracted from a set of scanning electron microscope (SEM) images. The nano-scale aperture of grain contacts, which is below image resolution, is accounted for in micro-CT based numerical calculations by assigning effective porosity and conductivity to individual voxels of the extracted grain contact network. A porosity reduction of grain contacts and open pore space as function of applied confining pressure is introduced, ...
Wettability is a key factor defining ultimate hydrocarbon recovery. Extensive experimentation is ... more Wettability is a key factor defining ultimate hydrocarbon recovery. Extensive experimentation is required to replicate the wetting state of reservoir rocks. This involves a rock sample wettability restoration procedure, including an aging step and a concept of an optimum aging time, in which asphaltene chemistry plays a major role. There are numerous reports on significance of various crude oil components and elements of asphaltene structure to their tendency to interact with the solid phase, though subject evidence is contradictory. We investigate a possible relationship between the composition of oil, kinetics of an aging process, and a change of sandstone rock wettability. Wettability state of the cores was monitored using low-field NMR relaxometry. The composition and key components of accumulated deposits were established by matching 1H solution-state NMR and X-band EPR spectra of deposits to the spectra of SARA (saturates-aromatics-resins-asphaltenes) fractions of aging fluids. We determined adsorpt...
Numerical flow simulation in shale, especially in the nanoscale porous system of a shale matrix, ... more Numerical flow simulation in shale, especially in the nanoscale porous system of a shale matrix, is still challenging because no imaging device can effectively describe the nanoscale porous structure of shale to satisfy both resolution and field of view (FOV). The resolution of an X-ray computed tomography (µ-CT) image is too low to detect the nanoscale features of porous structure in shale. The FOV of a focused ion beam scanning electron microcopy (FIB-SEM) image, on the other hand, is too small to capture the heterogeneity of a shale matrix. Therefore, we propose a semi-quantitative, Multiscale reconstruction strategy to build an image based network model of a shale sample with nanoscale resolution covering three orders of magnitude of FIB-SEM image volume. In this study, shale is considered a Multiscale porous media consisting of microscale and nanoscale structures. The microscale structures reflect the morphological features of organic matter, clay minerals, intergranular pores and micro-cracks that can be detected by µ-CT. The nanoscale features focus on the inner porous structure of organic matter and clay minerals that can be characterised using a scanning electron microcopy (SEM) or a FIB-SEM. nanoscale. Multiscale means reconstruction work that is carried out at the microscale and nanoscale separately, using the multiple-point statistics (MPS) method. Microscale reconstruction aims to recover the connections that are undetected among microscale objects due to the low resolution of the µ-CT image. Within the organic and clay phases, a nanoscale reconstruction is then carried out to model the nanoscale porous structure. Semi-quantitative means the segmented µ-CT image is used as conditional data in microscale reconstruction to maintain the reality of microscale structures. To relieve the heavy burden of data storage, a network modelling procedure is simultaneously undertaken alongside nanoscale reconstruction to transfer the reconstructed structure to a network model. Based on the established network model, flow simulation is undertaken by applying an extended Beskok-Karniadakis (B-K) model considering continuum, non-continuum and surface diffusion. The results show that the permeability ratio is affected by pressure, the molecule diameter of gas and surface diffusion.
Development of microneedles for unskilled and painless collection of blood or drug delivery addre... more Development of microneedles for unskilled and painless collection of blood or drug delivery addresses the quality of healthcare through early intervention at point-of-care. Microneedles with submicron to millimeter features have been fabricated from materials such as metals, silicon, and polymers by subtractive machining or etching. However, to date, large-scale manufacture of hollow microneedles has been limited by the cost and complexity of microfabrication techniques. This paper reports a novel manufacturing method that may overcome the complexity of hollow microneedle fabrication. Prototype microneedles with open microfluidic channels are fabricated by laser stereolithography. Thermoplastic replicas are manufactured from these templates by soft-embossing with high fidelity at submicron resolution. The manufacturing advantages are (a) direct printing from computer-aided design (CAD) drawing without the constraints imposed by subtractive machining or etching processes, (b) high-fi...
Clay‐rich deposits are commonly assumed to be aquitards which act as natural hydraulic barriers d... more Clay‐rich deposits are commonly assumed to be aquitards which act as natural hydraulic barriers due to their low hydraulic connectivity. Postdepositional weathering processes are known to increase the permeability of aquitards in the near surface but not impact on deeper parts of relatively thick formations. However, syndepositional processes affecting the hydraulic properties of aquitards have previously received little attention in the literature. Here, we analyze a 31 m deep sediment core recovered from an inland clay‐rich sedimentary sequence using a combination of techniques including particle size distribution and microscopy, centrifuge dye tracer testing and micro X‐ray CT imaging. Subaerial deposition of soils within these fine grained alluvial deposits has led to the preservation of considerable macropores (root channels or animal burrows). Connected pores and macropores thus account for vertical hydraulic conductivity (K) of m/s (geometric mean of 13 samples) throughout th...
Physica A: Statistical Mechanics and its Applications, 2018
Abstract X-ray computed tomography ( μ -CT) is considered to be the most effective way to obtain ... more Abstract X-ray computed tomography ( μ -CT) is considered to be the most effective way to obtain the inner structure of rock sample without destructions. However, its limited resolution hampers its ability to probe sub-micro structures which is critical for flow transportation of rock sample. In this study, we propose an innovative methodology to improve the resolution of μ -CT image using neighbour embedding algorithm where low frequency information is provided by μ -CT image itself while high frequency information is supplemented by high resolution scanning electron microscopy (SEM) image. In order to obtain prior for reconstruction, a large number of image patch pairs contain high- and low- image patches are extracted from the Gaussian image pyramid generated by SEM image. These image patch pairs contain abundant information about tomographic evolution of local porous structures under different resolution spaces. Relying on the assumption of self-similarity of porous structure, this prior information can be used to supervise the reconstruction of high resolution μ -CT image effectively. The experimental results show that the proposed method is able to achieve the state-of-the-art performance.
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service... more This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. Highlights High-and low-salinity brine was injected into a Berea sandstone core plug Micro-CT images of the core plug was taken before and after injection SEM-EDS analysis showed clay fines production Laboratory measurements showed an 80% decrease in permeability Image analysis show clay straining near the production end of the core plug
An elementary question in porous media research is in regard to the relationship between structur... more An elementary question in porous media research is in regard to the relationship between structure and function. In most fields, the porosity and permeability of porous media are properties of key interest. There is, however, no universal relationship between porosity and permeability since not only does the fraction of void space matter for permeability but also the connectivity of the void fraction. With the evolution of modern day X-ray microcomputed tomography (micro-CT) and advanced computing, it is now possible to visualize porous media at an unprecedented level of detail. Approaches in analyzing micro-CT data of porous structures vary in the literature from phenomenological characterization to network analysis to geometrical and/or topological measurements. This leads to a question about how to consistently characterize porous media in a way that facilitates theoretical developments. In this effort, the Minkowski functionals (MF) emerge from the field of statistical physics where it is evident that many physical processes depend on the geometry and topology of bodies or multiple bodies in 3D space. Herein we review the theoretical basis of the MF, mathematical theorems and methods necessary for porous media characterization, common measurement errors when using micro-CT data and recent findings relating the MF to macroscale porous media properties. This paper is written to provide the basics necessary for porous media characterization and theoretical developments. With the wealth of information generated from 3D imaging of porous media, it is necessary to develop an understanding of the limitations and opportunities in this exciting area of research.
The characterisation of heterogeneous porous media at multiple length scales typically requires t... more The characterisation of heterogeneous porous media at multiple length scales typically requires the classification of structure at some scale to allow the calculation of effective transport properties at a scale relevant for macroscopic description. While such a classification may be derived from various imaging methods, a shortcoming is often the simultaneous characterisation of the connectivity between regions representing different micro-structure. In this work we combine NMR based flow propagators with the simulations performed on corresponding reconstructed structure, and relate the NMR measurements to their simulated global and local representations to study fluid transport locally and the exchange between micro- and macro-porous regions. This is achieved by carrying out detailed lattice Boltzmann simulations and random walk method to track the displacements of tracers in each kind of region. Using Euclidean distance maps (EDT) we analyse the fluid invasion to regions of diffe...
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Papers by Christoph Arns