Abstract. The development of microfocused X-ray computed tomography (CT) devices enables digital imaging analysis at the pore scale. The applications of these devices are diverse in soil mechanics, geotechnical and geoenvironmental engineering, petroleum engineering, and agricultural engineering. In particular, the imaging of the pore space in porous media has contributed to numerical simulations for single-phase and multiphase flows or contaminant transport through the pore structure as three-dimensional image data. These obtained results are affected by the pore diameter; therefore, it is necessary to verify the image preprocessing for the image analysis and to validate the pore diameters obtained from the CT image data. Moreover, it is meaningful to produce the physical parameters in a representative element volume (REV) and significant to define the dimension of the REV. This paper describes the underlying method of image processing and analysis and discusses the physical properties of Toyoura sand for the verification of the image analysis based on the definition of the REV. On the basis of the obtained verification results, a pore-diameter analysis can be conducted and validated by a comparison with the experimental work and image analysis. The pore diameter is deduced from Young–Laplace's law and a water retention test for the drainage process. The results from previous study and perforated-pore diameter originally proposed in this study, called the voxel-percolation method (VPM), are compared in this paper. In addition, the limitations of the REV, the definition of the pore diameter, and the effectiveness of the VPM for an assessment of the pore diameter are discussed.
Water retention in granular soils is a key mechanism for understanding transport processes in the vadose zone for various applications from agronomy to hydrological and environmental sciences. The macroscopic pattern of water entrapment is mainly driven by the pore-scale morphology and capillary and gravity forces. In the present study, the drainage water retention curve (WRC) was measured for three different granular materials using a miniaturised hanging column apparatus. The samples were scanned using X-ray micro-computed tomography during the experiment. A segmentation procedure was applied to identify air, water and solid phases in 3D at the pore-scale. A representative elementary volume analysis based on volume and surface properties validated the experimental setup size. A morphological approach, the voxel percolation method (VPM) was used to model the drainage experiment under the assumption of capillary-dominated quasi-static flow. At the macro-scale, the VPM showed a good capability to predict the WRC when compared with direct experimental measurements. An in-depth comparison with image data also revealed a satisfactory agreement concerning both the average volumetric distributions and the pore-scale local topology. Image voxelisation and the quasi-static assumption of VPM are likely to explain minor discrepancies observed at low suctions and for coarser materials.
2D Granulometric method analyzed pore structure of CT images in 2 dimensions obtained from X-ray CT scanner.Then, Lattice Boltzmann Method for two-phase flow using Shan and Chen model was applied to same images analyzed for in-situ simulation. Flow condition with a capillary number of 10 -4 at inlet did not give enough pore pressure to seepage into pore size less than 9 voxels. Meanwhile, it was confirmed that the flow condition with a capillary number of 10 -3 at inlet could give enough pore pressure which LNAPL could seep into the pore with less than 9 voxels. Hence,
The objective of this study is to improve the understanding the migration mechanisms of Light Non-Aqueous Phase Liquids (LNAPLs) in porous media at the pore network scale. In this paper, an evaluation of trapped LNAPL in a pore structure after injection experiments coupled with micro focused X-ray Computed Tomography (MXCT) is presented. Image analysis of pore occupation by fluids from MXCT data was performed using different granular materials: glass beads and sandy soil. It can be observed that the trapping process is dependent on the pore structure. Specifically, LNAPL tends to be retained in larger pores in certain area where can work capillary pressure.
Abstract. The development of a micro-focused X-ray CT device enables digital imaging analysis at the pore-scale. The applications have been diverse, for instance, in soil mechanics, geotechnical and geoenvironmental engineering, petroleum engineering, and agricultural engineering. In particular, imaging of the pore space of porous media has contributed to numerical simulations for single and multi-phase flow, or contaminant transport, through the pore structure as three-dimensional image data. These obtained results are affected by the pore diameter so it is necessary to verify the image pre-processing for image analysis, and validate the pore diameters obtained from the CT image data. Besides, it is meaningful to produce the parameters in a representative element volume (REV) and significant to define the dimension of REV. This paper describes the underlying method of image processing and analysis and discusses the physical properties of Toyoura sand for the verification of image analysis based on the definition of REV. Based on the obtained verification results, pore diameter analysis can be conducted and validated by the comparison of the experimental work and image analysis. The pore diameter was deduced by Laplace’s law and the water retentively test for the drainage process. The referenced result sand perforated pore diameter proposed originally in this study, called the voxel-percolation method (VPM), are compared in this paper. The paper describes the limitation of REV, the definition of pore diameter, and the effectiveness of VPM for the assessment of pore diameter.
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