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Digital core analysis at multiple scales incorporating X-ray micro-computed tomography (μCT) imaging in different states in 3D, and registration of 2D SEM and SEM–energy-dispersive X-ray spectra (EDS) images into the 3D tomograms, offers an extensive and unique toolbox for characterising potential CO2 reservoir and seal candidates. μCT imaging allows the calculation of connected porosity, and subsequently properties such as permeability, formation factor, Archie's cementation component, drainage capillary pressure, and Swi can be determined digitally and pore-throat network models can be generated. Sub-micron scale features in the 3D image can be directly correlated with high-resolution scanning electron microscope (SEM) images using 2D-to-3D image registration. Additionally, the in situ mineralogy can be quantified by using an automated mineral and petrological analysis (SEM–EDS) system. The mineralogy determined in 2D by SEM–EDS can then be interpolated into the 3D image block for the direct identificat...

The structure of the porous three-dimensional reticulated pattern in the wing scales of the butterfly Callophrys rubi (the Green Hairstreak) is explored in detail, via scanning and transmission electron microscopy. A full 3D tomographic reconstruction of a section of this material reveals that the predominantly chitin material is assembled in the wing scale to form a structure whose geometry bears a remarkable correspondence to the srs net, well-known in solid state chemistry and soft materials science. The porous solid is bounded to an excellent approximation by a parallel surface to the Gyroid, a three-periodic minimal surface with cubic crystallographic symmetry I4₁32, as foreshadowed by Stavenga and Michielson. The scale of the structure is commensurate with the wavelength of visible light, with an edge of the conventional cubic unit cell of the parallel-Gyroid of approximately 310 nm. The genesis of this structure is discussed, and we suggest it affords a remarkable example of templating of a chiral material via soft matter, analogous to the formation of mesoporous silica via surfactant assemblies in solution. In the butterfly, the templating is achieved by the lipid-protein membranes within the smooth endoplasmic reticulum (while it remains in the chrysalis), that likely form cubic membranes, folded according to the form of the Gyroid. The subsequent formation of the chiral hard chitin framework is suggested to be driven by the gradual polymerisation of the chitin precursors, whose inherent chiral assembly in solution (during growth) promotes the formation of a single enantiomer.

Tight gas reservoirs exhibit storage and flow characteristics that are intimately tied to depositional and diagenetic processes. As a result, exploitation of these resources requires a comprehensive reservoir description and characterization program to identify properties which control production. In particular, tight gas reservoirs have significant primary and secondary porosity and pore connectivity dominated by clays and slot-like pores. This makes them particularly susceptible to the effects of overburden stress and variable water saturation. This paper describes an integrated approach to describe a tight gas sandstone at the pore scale in 3D. In particular, the primary and secondary porosity of a tight gas sandstone are identified and quantified in three dimensions using 3D X-ray micro-CT imaging and visualization of core material at the pore scale. 3D images allow one to map in detail the pore and grain structure and interconnectivity of primary and secondary porosity. Once the tomographic images are combined with SEM images from a single plane within the cubic data set, the nature of the secondary porosity can be determined and quantified. In-situ mineral maps measured on the same polished plane are used to identify different microporous phases contributing to the secondary porosity. Once these data sets are combined, the contribution of individual clay minerals to the microporosity, pore connectivity, and petrophysical response can be determined. Insight into the producibility may also be gained. This illustrates the role 3D imaging technology can play in a comprehensive reservoir characterization program for tight gas.

X-ray micro-CT is used here to visualize the distribution of melamine–urea–formaldehyde adhesive in the wood composite, particleboard, and examine changes in adhesive distribution on wood particles (flakes) before and after pressing. CT and scanning electron microscopy of unpressed, wax-covered, wood flakes reveals that adhesive is evenly distributed on flakes, although it does not completely cover all surfaces. Adhesive on these wood flakes migrates during pressing forming more continuous glue-lines in areas of the composite where flakes are pressed closely together and more discontinuous glue-lines where inter-particle contact is poorer. Adhesive accumulates in small, but not very large voids, and also in cracks in wood flakes and around very small wood particles. These observations accord with previous observations of adhesive distribution in pressed wood composites. In addition, CT reveals that resin accumulates in capillary channels within the splintered ends of wood flakes and at the base of composite samples. The orthogonal variation in volume of the composite occupied by adhesive, wood and void space was quantified using maximal sphere modelling, and anisotropy in the distribution of these phases in the x, y and z directions was quantified using chord length analysis. These numerical techniques reveal that adhesive is more closely associated with wood flakes than void space, despite its tendency to migrate during pressing. As a result, adhesive is mainly aligned in the same x–y direction as wood flakes forming an anisotropic discontinuous network. We conclude that X-ray micro-CT is a powerful tool capable of providing new insights into the distribution of adhesive in wood composites.

Tomographic imaging can now be routinely performed over three orders of magnitude in length scale with correspondingly high data fidelity. This capability, coupled with the development of advanced computational algorithms for image interpretation, three-dimensional visualization, and structural characterization and computation of physical properties on image data, allows for a new numerical laboratory approach to the study of real complex materials: the Virtual Materials Laboratory. Numerical measurements performed directly on images can, in many cases, be performed with similar accuracy to equivalent laboratory measurements, but also on traditionally intractable materials. These emerging capabilities and their impact on a range of scientific disciplines and industry are explored here.

Oriented strand board (OSB) is an important wood composite used in situations where fungal decay and termite attack can occur. To counter these threats, powdered zinc borate biocide is commonly added to OSB. The effectiveness of biocides depends on their even distribution within composites and resistance to leaching, but little is known about the distribution of zinc borate in OSB. Zinc is denser than wood and it should be possible to map its distribution in OSB using X-ray micro-CT. We test this hypothesis and chemically register zinc in OSB using SEM-EDX. Zinc borate particles aggregated at the wood-adhesive interface in OSB, creating interrupted lines of zinc oriented in the x-y plane. Zinc borate particles were also found in the lumens of wood cells. Zinc was distributed throughout OSB, although slightly less was present in the core of the composite than in surface layers. A network of zinc remained in OSB after leaching in water. The resistance of zinc to leaching may be due to its incorporation in glue-lines within OSB, in addition to its low water-solubility. We conclude that X-ray micro-CT is a powerful tool for studying the distribution of zinc in OSB and other wood composites containing zinc borate.

We demonstrate the capability of X-ray micro-computed tomography to image the micro-structure of human cortical bone. At 5 μm voxel size we observe the complex morphology of the Haversian network in three dimensions. The local thickness of Haversian canals is measured using a maximal sphere algorithm and found to have a bimodal signature and a mean radius of 19.2 μm. The intra-cortical porosity due to Haversian canals is measured as 3.0%. Both results are in agreement with traditional histomorphometric measurements. We show that at higher resolutions one can resolve the spatial distribution of lacunae in cortical bone. © 2004 Elsevier B.V. All rights reserved.

This article presents a three-stage approach, combining novel and traditional algorithms, for the segmentation of images of porous and composite materials obtained from X-ray tomography. The first stage is an anisotropic diffusion filter which removes noise while preserving significant features. The second stage applies the unsharp mask sharpening filter which enhances edges and partially reverses the smoothing that is often a consequence of tomographic reconstruction. The final stage uses a combination of watershed and active contour methods for segmentation of the grey-scale data. For the data sets we have analysed, this approach gives the highest quality results. In addition, it has been implemented on cluster-type parallel computers and applied to cubic images comprising up to 20003 voxels.

The inability of certain antigen processing mutant cell lines to present intact proteins to T cells and to form SDS-stable MHC class II dimers has been shown to result from defective expression of HLA-encoded DMA and DMB genes. We have utilized some of these mutants to determine species compatibility of antigen presentation components. Mouse MHC class II I-A d cDNA was transfected into the human B cell lymphoblastoid cell lines 8.1.6, 7.9.6 (a mutant cell line derived from 8.1.6) and an independent deletion mutant T2 (called 8.1.6d, 7.9.6d and T2.d respectively). These cells were then examined for various functions in antigen presentation. Interestingly, none of the cells transfected with I-A d presented peptides derived from intact proteins to specific T cell hybridomas. However, presentation of synthetic peptides by these cells was normal. The ability to form SDS-stable dimers was dramatically reduced in the transfectants. In addition, I-A d molecules at the cell surface appeared loaded predominantly with the invariant chain peptides, CLIP. These properties of the I-A d transfectants are identical to those described for HLA class II molecules expressed in HLA-DM mutants. Perhaps the most interesting finding was the inability of I-A d in 8.1.6 to present protein antigens. Since 8.1.6 cells present antigens to HLA-DR, DP, DQ-restricted T cells and also have intact HLA-DM and invariant chain (Ii) functions, these results argue that some component of human antigen processing machinery is incompatible with I-A d molecules.

In geological storage of CO2 there are four main trapping mechanisms; structural, dissolution, mineral and residual trapping. While structural and dissolution trapping depend on the large scale structure of the reservoir, both residual and mineral trapping are strongly influenced by geometry at the pore scale. The dominant mechanism for residual capillary trapping is snap off which depends largely on the interconnectivity of the pore space and ratio of the pore throats to pore bodies. Mineral trapping depends largely on the surface area and mineralogy of the rock. Digital core analysis makes it possible to directly enumerate the detailed pore and mineral phase structure of core material in 3D. Flooding experiments enable the amount and microscopic distribution of residual fluid phases to be directly imaged in 3D. In this paper the pore scale properties associated with mineral and residual capillary trapping are directly enumerated using core material from the CO2CRC Otway CO2 storage project in Australia. Surface areas associated with varying mineral phases are quantified. 3D pore network characteristics are derived from the image data which allow the quantification of the pore network structure (e.g., interconnectivity) and the pore geometry (pore/throat size, pore shape, aspect ratio). Heterogeneity of the permeability and anisotropy are calculated directly. The amount of residual non-wetting phase of analog fluid pairs is directly measured on Otway core material after flooding at the pore scale in 3D. The microscopic distribution of the residual non-wetting phase within the pore space is quantified and individual pore occupancies defined. This information will provide a better understanding of recovery mechanisms and assist in the design and implementation of CO2 flooding processes. Comparison of individual pore occupancies based on 3D image data provides a foundation for quantitative comparison of experiment to pore scale modeling and enable testing and calibration of pore network predictions of CO2 storage.

Abstract The prediction of hydrocarbon recovery is related to both the detailed pore scale structure of core material and fluid interfacial properties. An increased understanding of displacement efficiencies and overall recoveries requires an ability to characterize the pore structure of reservoir core in 3D and to observe fluid distributions at the pore scale. Micro-CT imaging is capable of acquiring 3D images of the pore structure of sedimentary rock with resolutions down to the micron scale. This allows the 3D pore-space of many reservoir rock samples to be imaged at the pore scale. The 3D porespace of tighter clastics and carbonate core material includes a significant proportion of microporosity—pores at the submicron scale which are not directly accessible via current micro-CT capabilities. Porosity at all scales can affect fluid flow, production, recovery data and log responses. It is important to characterize pore structure and connectivity in a continuous range across over six decades of length scales (from nm to cm) to better understand these petrophysical and production properties. In this paper we describe 2D and 3D imaging studies of reservoir core via micro-CT coupled with complementary petrographic techniques (thin section, mercury intrusion) and high resolution focused ion beam (FIB) scanning electron microscopy studies of a range of reservoir core. Results are given which illustrate the importance of pore structures at varying scales in determining petrophysical properties. Microtomography is then used to observe pore scale fluid distributions within the core material. Displacement experiments under controlled wettability conditions are undertaken. The local pore-scale fluid distributions identified via 3D tomographic imaging experiments. These results provide insight into the role of rock microstructure in determining recovery and production characteristics. Introduction Micro-CT (µ-CT) imaging [1,2] is becoming increasingly popular for characterising many macroscopic properties of porous media. From µ-CT images one is able to compute petrophysical properties such as porosity, permeability, conductivity, elasticity, and mercury injection capillary pressure (MICP). Rock properties derived from fragments of a range of cores including homogeneous and reservoir sands have been compared with conventional laboratory measurements and shown to be in good agreement [3,4]. In more complex cores (e.g., carbonates, heterogeneous sands, tight gas) one must consider the role of pore structure in a continuous range across over many decades of length scales (from nm to cm) to better understand these processes. For example, in carbonate rocks, the processes of sedimentation and diagenesis produce a complex spatial distribution of pores and pore connectivity across several decades of length scales. Therefore developing a reliable petrophysical interpretation for predicting the transport properties and producibility of complex cores such as carbonates remains difficult. In this paper we describe 2D and 3D imaging studies of complex reservoir core material via µ-CT coupled with complementary petrographic techniques (thin section, SEM) and high resolution focused ion beam tomography (FIBT). We utilize a newly developed image registration technique for aligning high-resolution 2D microscopy (SEM, Optical) images of core thin sections with the corresponding region of the micro-CT 3D image of the core. The integration of aligned high resolution (nm scale) data with 3D µ-?CT data has the potential to increase the accuracy of the physical properties predicted from the 3D µ-CT image analysis.

A microcomputed tomography (μCT) facility and computational infrastructure developed at the Department of Applied Mathematics at the Australian National University is described. The current experimental facility is capable of acquiring 3D images made up of 2000 3 voxels on porous specimens up to 60 mm diameter with resolutions down to 2 μm. This allows the three-dimensional (3D) pore-space of porous specimens to be imaged over several orders of magnitude. The computational infrastructure includes the establishment of optimised and distributed memory parallel algorithms for image reconstruction, novel phase identification, 3D visualisation, structural characterisation and prediction of mechanical and transport properties directly from digitised tomographic images. To date over 300 porous specimens exhibiting a wide variety of microstructure have been imaged and analysed. In this paper, analysis of a small set of porous rock specimens with structure ranging from unconsolidated sands to complex carbonates are illustrated. Computations made directly on the digitised tomographic images have been compared to laboratory measurements. The results are in excellent agreement. Additionally, local flow, diffusive and mechanical properties can be numerically derived from solutions of the relevant physical equations on the complex geometries; an experimentally intractable problem. Structural analysis of data sets includes grain and pore partitioning of the images. Local granular partitioning yields over 70,000 grains from a single image. Conventional grain size, shape and connectivity parameters are derived. The 3D organisation of grains can help in correlating grain size, shape and orientation to resultant physical properties. Pore network models generated from 3D images yield over 100000 pores and 200000 throats; comparing the pore structure for the different specimens illustrates the varied topology and geometry observed in porous rocks. This development foreshadows a new numerical laboratory approach to the study of complex porous materials.

In human and mouse, the germline contains a tandem array of highly homologous variable (V) gene elements which encode part of the antigen-binding region of the antibody protein. During evolution this array apparently arose by gene duplication followed by diversification of duplicated genes via point mutation and recombination. Analysis of germline V gene sequences using a novel algorithm shows that major recombination sites coincide with the borders of the leader intron and the cap site, consistent with the hypothesis that over evolutionary time cDNA derived by reverse transcription of pre-mRNA in B lymphocytes has recombined with germline DNA.

The cDNA sequence of dihydropteridine reductase (DHPR) showed that the enzyme has four cysteine residues.1,2 These are cys26, cys85, cys104 and cys161. Evidence from titration experiments of human and rat DHPR with thiol reagents and platinum II complexes suggested that when one of the cysteines was masked by addition of NADH then it did not react with these reagents and the enzyme was protected from inactivation.3,4 In order to see if one of these cysteine residues was the proton source for the enzymic reduction of quinonoid dihydropterin substrates, we investigated the effect of replacing the cysteine residues by serine residues, which are weaker acids, and we examined the kinetics of the mutant proteins.