## 4 Results
### Pore System and Pore Size
#### 4.3.1 Inorganic Pores  
Inorganic interP pores are the pore spaces between detrital particles such as feldspar, quartz, and clay platelets formed through sedimentation and diagenesis. InterP pores can also be found in authigenic minerals, including quartz, calcite, pyrite, and siderite [21]. The size and shape of interP pores are influenced by detrital type, grain size, sorting, and particle arrangement [21]. InterP pores between rigid grains such as quartz and feldspar are well-developed, typically exhibiting a polygonal shape and lacking obvious orientation. Additionally, the edges of these pores are usually relatively straight (Figures 6K and 8A,B). The dissolution of the edges of easily soluble detrital particles, such as feldspar and calcite, results in a zigzag appearance of the pore edges (Figure 6J,L and Figure 8A,J). The size of interP pores ranges from 10 nm to 600 nm, with an average of 154 nm, and can reach several micrometers. Figure 7: Box plots of the proportion of POM and MSB to total OM in mudstones, mudstones with siltstone interlayers, and sand-silt intervals. Some interP pores between rigid particles and clay minerals, as well as among clay platelets, were preserved in compaction-protected shadows. The pores between clay platelets are often elongated, triangular, or irregular in shape (Figure 8C,D). The interP pores between clay platelets tend to be oriented due to compaction (Figure 8D). The pore sizes between rigid particles and clay minerals, as well as among clay platelets, range from 5 nm to 200 nm, with a maximum size of up to 800 nm and an average size of 54 nm. Inorganic intra-particle pores (intraPs) are also common in the Yanchang shales. These include pores or cleavages within detrital grains and authigenic minerals, as well as pores within pyrite and clay aggregates. IntraP pores can be categorized into residual primary intraP pores and diagenetic intraP pores. Pores and cleavages within feldspar, calcite, clay minerals, mica, and fossils were preserved under compaction as residual intraP pores (Figure 8A,D,K). In contrast, intracrystalline pores within pyrite and clay aggregates (Figure 8E-H), intraP pores, cleavages, and dissolution pores within authigenic calcite, dolomite, feldspar, and siderite (Figure 6H,J,L and Figure 8I-L) are classified as diagenetic intraP pores. The size of most intraP pores ranges from 2 nm to 100 nm, with some reaching  
Figure 8: SEM photographs showing interP and intraP pores. (**A**) Primary interP pores and intraP pores, well Y8. (**B**) Primary interP pores and dissolution pores, well Y8. (**C**) Primary interP pores in clay platelets and intraP pores in clay aggregates, well Y11. (**D**) Primary interP pores in clay platelets and siderites, and intraP pores in clay aggregates, well Y5. (**E,F**) IntraP pores in clay aggregates, well Y8. (**G**) IntraP pores within pyrite aggregates, well Y10. (**H**) IntraP pores within pyrite aggregates, well W3. (**I**) Dissolution pores within feldspar, well W3. (**J**) Dissolution pores of siderite, interP pores, and intraP pores, well Y5. (**K**) Cleavage and dissolution pores in feldspar, well W3. (**L**) Dissolution pores in feldspar and siderite, well Y10. Red arrows—interP pores, yellow arrows—intraP pores, purple arrows—dissolution pores. several micrometers. The intracrystalline pores within authigenic pyrite are relatively large, with pore sizes typically ranging from 20 nm to 400 nm (Figure 8E,F). The dominant inorganic pore types and sizes in sand-silt intervals and mudstones exhibit significant differences. Sand-silt intervals, characterized by a high content of rigid detrital such as feldspar and quartz, as well as larger grain sizes, have rigid particles that support each other to resist compaction. This results in a greater number of residual interP pores being preserved in compaction-protected shadows.