X-ray CT analysis of pore structure in sand

Abstract

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.

Pore-scale tomography and imaging: applications, techniques and recommended practice

“…Last but not least, Mukunoki et al (2016) present research of CT investigations of structures in unconsolidated sand, relevant for environmental engineering.…”

Micro- and macro-scale water retention properties of granular soils: contribution of the X-Ray CT-based voxel percolation method

“…Nonetheless, two-phase flow simulations at the pore scale are still numerically costly and concerns remain regarding the capability to image soil samples at the REV size and directly compute the core-scale properties of these 3D digitalised porous media. In this framework, morphological approaches represent a promising alternative to exploit large volumes of 3D µCT images but at the cost of highly simplified physical description (Hilpert and Miller 2001;Vogel et al 2005;Mukunoki et al 2016). Berg et al (2016) showed that the morphological approach produced a good prediction of the relative permeability curve of sandstone rock for drainage steady-state experiment but it failed for imbibition conditions.…”

“…Berg et al (2016) showed that the morphological approach produced a good prediction of the relative permeability curve of sandstone rock for drainage steady-state experiment but it failed for imbibition conditions. Recently, Mukunoki et al (2016) introduced an original method called the voxel percolation method (VPM), which enables an a priori estimate of the retention curve based on the solid-pore binary image obtained from µCT. The WRC predicted by VPM compared fairly with experimental WRC, provided that the computation was carried out in a sufficiently large image sample.…”

“…To achieve this goal, three different materials were selected and their pore structure and water distribution were visualised by µCT during HCT retention curve characterisation. The VPM model (Mukunoki et al 2016) was considered as representative example of morphological approach. In the first part of this paper, the drainage WRC determination using a mini HCT apparatus is described.…”

Evaluation of Imbibition Process in Porous Media by Invaded Percolation Probability

“…This approach has also been employed to analyze pore structure [5], [6]. Recently, detailed shape of pores and frequency of pore size have studied directly due to the development of observation apparatus such as a high-resolution X-ray computed tomography (CT) scan [7].…”