Articles | Volume 7, issue 3
Solid Earth, 7, 929–942, 2016

Special issue: Pore-scale tomography & imaging - applications, techniques...

Solid Earth, 7, 929–942, 2016

Research article 09 Jun 2016

Research article | 09 Jun 2016

X-ray CT analysis of pore structure in sand

Toshifumi Mukunoki1, Yoshihisa Miyata2, Kazuaki Mikami3, and Erika Shiota4 Toshifumi Mukunoki et al.
  • 1X-Earth Center, Faculty of Advanced Science and Technology, Kumamoto University, 1-39-2 Kurokami Kumamoto city, Kumamoto, Japan
  • 2Department of Civil and Environmental Engineering, National Defense Academy, 1-10-20 Hashirimizu, Yokosuka, Japan
  • 3Japan Oil, Gas and Metals National Corporation, 1-2-2 Hamada Mihama-ku Chiba City, Chiba, Japan
  • 4Graduate School of Science and Technology, Kumamoto University, 1-39-2 Kurokami Kumamoto city, Kumamoto, Japan

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.

Short summary
In this study, a specimen of sand was scanned to evaluate pore structure quantitatively using a micro-focused X-ray CT scanner. The representative volume to perform reasonable image analysis for sand was discussed, and then the spatial distribution of pore diameter in 3-D was visualized and evaluated quantitatively by granulometric image analysis. Also, the voxel-percolation analysis was newly proposed in this study to assess capillary pressure and saturation degree by pore diameter analyzed.