## 2 _Introduction_  
Represented by a lattice of pores connected by throats, the void in rock masses has a fundamental impact on the physical and mechanical properties of the rock. Sedimentary rock mass is mainly composed of pores and solid parts. To evaluate the reservoir properties of sedimentary rock, a quantitative analysis in terms of the pore morphology is required, which entails the characterization of both the dimensions and shapes of the pores and the connecting throats. [PERSON] et al. [1] performed characterization studies on the microstructure of rock masses and analyzed the spatial arrangement of pores and solids on the rock slices. Thanks to the development of image processing technologies, scanning electron microscopy and image processing technologies were applied to quantitatively reveal the pore structure of geotechnical materials [2; 3; 4]. [PERSON] et al. [4] tried to quantify the pore morphology of different carbonate samples based on the digital analyses of two-dimensional images from thin sections taken under the environmental scanning electron microscope (ESEM). The effect of the pore morphology on the porosity and permeability was also discussed. [PERSON] et al. [5] applied femtosecond laser cutting so as to look into the intrapore structures of calcareous sand grains of various sizes. As they concluded, small pores outnumbered large pores and the former prevailed in terms of volumetric fraction. [PERSON] et al. [6] applied X-ray diffraction, scanning electron microscopy and mercury intrusion porosimetry to study the effect of zinc (Zn) concentration on the pore-size distribution of zinc-contaminated kaolin clay when the clay was stabilized by a cement additive. X-ray tomographic imaging and relevant analytic technologies were also applied to study the multiphase flow and displacement inside a porous material [7]. In recent years, significant improvement has been made with regard to the X-ray light source technology in CT scanning. Meanwhile, driven by oil and gas exploration, pollutant migration, coal mining, and the geological storage of CO\({}_{2}\), high-resolution industrial CT has been increasingly used to reveal the pore morphology of rocks [8; 9; 10]. The application of CT technology enables researchers to look into the microstructures of geotechnical materials [11; 12; 13; 14; 15]. [PERSON] et al. [16] applied the mercury injection capillary pressure (MICP) test, nuclear magnetic resonance (NMR), scanning electron microscopy (SEM) and X-ray computed tomography (CT) to investigate the geometry and topology of the pore network of low permeability carbonate cap rocks, during which the CT scanning proved to be competent to characterize the geometry, topology and fractal dimension of the pore network in the rocks. In other developments, X-ray computed tomography (CT) was applied to investigate the damage cracking behavior of rock and soil aggregate (RSA) under uniaxial compressive loading [15]. [PERSON] et al. [17] proposed a finite volume-based methodology for the analysis of two-phase flow using micro-CT images of porous media. In summary, the primary advantage of CT scanning is to image a sample in a three-dimensional and non-destructive manner. It uses X-rays to create cross-sectional pictures (\"slices\") of the sample. The slices can either be displayed individually in two dimensional form or stacked together to generate a 3D imaging that can reveal the internal structure of the sample. Furthermore, with the help of relevant softwares and algorithms such as Avizo, VGStudio MAX and Pore3D, quantitative 3D analysis can be performed for certain features of interest for the sample. In geoscience, the features of interest include the pore characteristics, morphological characteristics, mineral composition, crack propagation, fluid flow analysis and the reconstruction of fossils [18]. The present work studies the pore network of two types of sedimentary rocks, i.e., carbonate rock and sandstone.