Holger Averdunk

Developing a virtual materials laboratory

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.

3D porosity and mineralogy characterization in tight gas sandstones

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 ar...

3D characterisation of potential CO 2 reservoir and seal rocks

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, Archies 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 identification of minerals with contrasting X-ray attenuation. The 3D data can be readily displayed using 3D visualisations that show the pore connectivity, 3D mineralogy, geological structures, and incorporating the pore-throat network model, SEM, and 2D in situ mineral map. Additionally the porosity and flow pathways of a potential seal rock can be characterised at the nanoscale (pores 10–30 nm) using focussed ion beam SEM (FIBSEM) imaging. The behaviour of the potential reservoir and seal rocks during interaction with supercritical CO2 and water can be directly investigated by coupling digital core analysis with a high-pressure cell. Multiple images can be collected of the same plug before, during and after interaction with CO2 and water to directly characterise in 3D the CO2 trapping, and changes to the pore/throat geometries and mineralogy owing to interactions with the CO2.

Quantitative properties of complex porous materials calculated from X-ray μCT images

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 20003 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.

Visualizing the Microdistribution of Zinc Borate in Oriented Strand Board Using X-Ray Microcomputed Tomography and SEM-EDX

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.