Three-Dimensional Characterization of Inner Pores in Calcareous Sand Particles

The shape of the calcareous sand particles found near the South China Sea is complex. The edges of these particles are prominent, and the surface pore and inner pore structures are developed. In order to accurately characterize the three-dimensional (3D) shape of the pores in calcareous sand particles, high-precision tomographic images of the calcareous sand particles were obtained using a high-precision X-ray μCT scanning technique. The 3D image of the calcareous sand particles was reconstructed through cutting, denoising, binarization, and other operations on the original CT scan image. As the shape of calcareous sand particles is irregular, it is difficult to extract the internal pores directly. In this paper, a series of algorithms, such as 3D closing algorithm, were used to reconstruct the interior structure of calcareous sand. According to the appearance characteristics of the calcareous sand particles, porosity of the inner pores, shape of the pore size distribution curve, and fractal dimension, calcareous sand particles can be roughly classified into two types. The first type of calcareous sand particles has more gullies on the surface; its inner pores are more developed. The inner pores of the second type of calcareous sand particles are less developed and have lower connectivity. The porosity and pore size distribution curves of the two types of calcareous sand particles are significantly different. Furthermore, it is found that pores in the calcareous sand particles conform to the 3D fractal characteristics, and the value of the fractal dimension is positively correlated with the value of porosity. In order to deeply study the connectivity of inner pores in calcareous sand particles, the space network model of the inner pores was obtained by calculating the distance map. It can be concluded that all the distribution of the coordination number of the calcareous sand particle network model has the same general trend. Additionally, owing to the difference in pore morphology between the two types of calcareous sand particles, the distribution of their coordination numbers is slightly different. © 2019, Editorial Board of Journal of Tianjin University(Science and Technology). All right reserved.