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RESEARCH PRODUCT

The Effect of Tomography Imaging Artefacts on Structural Analysis and Numerical Permeability Simulations

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Fluid flow phenomena in porous materials can be found in many important processes in nature and in society. In particular, fluid flow through a porous medium contribute to several technological problems, e.g. extraction of oil or gas from porous rocks, spreading of contaminants in fluid-saturated soils and certain separation processes, such as filtration (Torquato, 2001). In paper and wood industry single and multi phase fluid flow properties in porous media play important roles related to manufacturing process and product development. The general laws describing creeping fluid flows are well known. However, a detailed study of fluid flow in porous heterogeneous media is complicated. This is a direct consequence of the often very complex, internal micro-scale structures of these materials. That is, the interplay between fluid flow and complex internal structure at the micro-scale gives rise to the effective fluid flow properties at the macro-scale. Traditionally, efforts for analysing fluid flow properties by means of modelling are based on using regular pore geometries that may possess the bulk properties of the actual medium and are simple enough to allow for analytic solution of the relevant transport equations. However, the development of imaging techniques based on computerised x-ray micro-tomography (CXμT) together with advanced numerical techniques have made it possible to analyse structural and transport properties of complex materials based on 3D digitalisation of their real microstructures (Coles et al., 1998; Samuelsen et al., 2001; Goel et al., 2002; Thibault & Bloch, 2002; Holmstad et al., 2003; Rolland et al., 2005; Goel et al., 2006; Stock, 2009). X-ray tomography is a non-invasive and non-destructive imaging method where individual x-ray images recorded from different viewing directions are used for reconstructing the internal 3D structure of the object of interest (Stock, 2009). Although a great opportunity to materials research, CXμT also poses new challenges. The imaging method produces noise, edge blurring, and various other artefacts that may distort the 3D reconstruction of the sample structure and thus result in unrealistic analysis results. In various industrial and scientific applications an effective material property, permeability, is used for describing the ability of porous materials to transmit fluids. Permeability coefficient for single phase creeping fluid flow through a porous media is defined by the phenomenological law by Henry Darcy as the proportionality constant between the average fluid velocity and applied pressure gradient (Darcy, 1856). The analytical approaches to analyse permeability are often confined to simplified sample geometries. Some of the