## 3 Results
### Pore Types and Pore Throat Characteristics
#### 3.2.2 Nano-Scale Pore Throats  
For the He8 section of the study area, pores and throats developed in the stratum are mainly intercrystalline pores of clay minerals, intergranular throats between secondary overgrowth quartz grains, and microcracks in a small amount of quartz grains. The intergranular pores of minerals are dominated by illite intercrystalline pores and kaolinite intercrystalline pores. Based on the SEM image of the study area and Matlab, the pore size distribution and pore throat radius of every sample in the study area were quantitatively analyzed. However, due to the limitations of SEM, a complete and macroscopic understanding of the sample is absent. So, through combining high-pressure mercury injection experiments with Matlab, the analysis of the pore throat distribution of the whole tight sandstone is systematic and comprehensive. The research method is similar to that of the micron pore throat. However, for the nano-pore throat, throat distribution and size are key points, and three main pore throats are respectively flake throats between the overgrowth quartz grains (Figure 6a), the book-like intercrystalline pores of kaolinite (Figure 6b), and the intercrystalline pores of the illite (Figure 6c). First, the SEM images are binarized (Figure 6a-c) by the 'Color Thresholder' application in Matlab, and the corresponding binary  
Figure 5: Relationship between average pore throat coordination number and porosity and the permeability of tight sandstone. images are shown in Figure 6d-f. Furthermore, according to functions 'bwlabel' and 'bwarea' and related codes, the pore throat size distribution is constructed (Figure 6g-i). Figure 6g-i shows that the different color areas represent the different pore areas, which are identified by Matlab. Through detailed statistics of various types of pore throats in the study area, the pore throat distribution histogram of the samples is shown in Figure 7. Pore throat statistics consist of illite intercrystalline pores and kaolinite intercrystalline pores, overgrowth quartz intergranular pores, and quartz grains intergranular pores and microcracks in the study area (Figure 7). In Figure 7, the orange and purple curves represent the intercrystalline pores of clay minerals (intergranular pores of illite and kaolinite). The pore throat radius is mainly concentrated between 0 nm and 600 nm, and is mainly distributed at about 300 nm. The blue curve represents the overgrowth quartz intergranular pores. The pore throat radius mainly ranges from 300 nm to 1200 nm. On the whole, the tight sandstone throat radius of the study area is mainly concentrated in the 200-1000 nm range. A quantitative analysis of the scanning electron microscope images in Matlab can clearly analyze  
Figure 6: SEM image, binary image, and pore distribution image of pore throat in the He8 Section. (**a**) SEM image of intergranular pores of overgrowth quartz; (**b**) SEM image of kaolinite intercrystalline; (**c**) SEM image of illite intercrystalline; (**d**) binary image of intergranular pores of overgrowth quartz; (**e**) binary image of kaolinite intercrystalline; (**f**) binary image of illite intercrystalline; (**g**) pore throat distribution of intergranular pores of overgrowth quartz; (**h**) pore throat distribution of kaolinite intercrystalline; (**i**) pore throat distribution of illite intercrystalline. the various types of pore throat radius distribution, including the distribution range, pore throat size distribution, and pore and throat characteristics of every image. However, the overall tight sandstone distribution is poorly fitted on this method. Therefore, combined with the characteristics of high-pressure mercury intrusion curves, the distribution characteristics of the tight sandstone throat can be well displayed in every dimension (Figure 8). Figure 8 shows the pore throat radius distribution of a whole sample measured by high-pressure mercury intrusion.