## 4 Results and Discussion
### Characteristics of the Shale Reservoirs and Their Influencing Factors
#### 4.3.2 Shale Pore Types  
Pore types and structural features are the main factors influencing the physical properties of shale reservoirs. Here, we investigated the pore structure characteristics of 11 shale samples (Table 1). Based on systematic studies of pore types in the Barnett Shale, previous studies have classified shale reservoir pores into three types based on the relationship between mineral matrix pores and particles [25; 47]: interparticle pores, intraparticle pores, and organic pores. Subsequent researchers further classified microfractures as a type of shale pore [48; 49]. Here, based on our microscopic observations, we classified pores of the Dalong shales from well ED-2 as organic pores, non-organic pores, or microfractures. Pore types, morphologies, sizes, and connectivities in the Dalong Formation shales vary significantly due to differences in organic matter type, TOC content, and mineral composition. 1. Organic pores  
Organic pores are nanoscale pores formed within organic grains after hydrocarbon generation and expulsion [24]. Our SEM observations revealed that many organic pores had developed in the siliceous shale samples of the Dalong Formation. These pores were bubble-like, elliptical, or slit-shaped, spanned a wide range of sizes, and showed obvious differences between samples. We studied the development of organic pores in three sets of samples, summarized individually here. Shales in the first set contained 5-6 wt.% TOC and had moderate quartz contents of 56-75% (Figure 8a-d). In these samples, organic pores were mostly bubble-like or elliptical,  
Figure 7: (**a**) Porosity distribution, (**b**) Permeability vs. porosity, (**c**) Porosity vs. TOC, (**d**) Porosity vs. mineral contents in the Dalong Formation shales. evenly distributed within the organic particles, and generally smaller than 50 nm. Those that developed at the edge of an organism retained their original biomorphology, and some are connected to form relatively large, slit-shaped pores (Figure 8a). Others developed from solid bitumen, either within intercrystalline pores of pyrite framboids (Figure 8b) or in the interparticle pores between rigid mineral grains (Figure 8c). Finally, organic pores also developed from mixtures of organic matter and clay minerals (Figure 8d). Shales in the second set contained <5 wt.% TOC and >80% quartz (Figure 8e-h). In these samples, organic pores were interconnected or collapsed to form elliptical or worm-like pores, mostly sized 50-600 nm, though a few were as small as 20-50 nm (Figure 8e,f). These pores formed when the organic matter reached an over-mature stage (2.56-2.79% \(R_{\mathrm{o}}\)) and began producing large amounts of hydrocarbons, thus resulting in abundant organic pores. Some organic pores supported by siliceous mineral particles were well preserved, retaining uncompressed elliptical shapes (Figure 8f). Organic pores developed from humic kerogen in type-II\({}_{1}\) organic matter developed along the edge of the organic matter, rather than within it (Figure 8g,h). Shales in the third set contained >10 wt.% TOC and <56% quartz (Figure 8i-l). These shales had well-developed bubble-like or elliptical organic pores, generally smaller than 50 nm. Due to the varieties of organic micro-components and different hydrocarbon generation capacities, the development of organic pores within different organic particles of these Dalong Formation shales varied significantly. Organic pores were unevenly distributed within the organic matter (Figure 8j), and pore sizes were varied (Figure 8k). Figure 8: Organic matter distributions, pore morphologies, and pore development characteristics of Dalong Formation shales with (**a–d**) Moderate TOC and quartz contents, (**e–h**) Low TOC and high quartz contents, (**i–l**) High TOC and low quartz contents. (**a**) Isolated and interconnected organic pores (yellow arrow) developed within organic matter (1229.6 m depth in well ED-2).