## 4 Results and Discussion
### Pore Structure Quantitative Characteristics  
#### 4.2.1 LTNA Isotherms and Pore Geometry  
On the basis of LTNA isotherm curve classification proposed by the IUPAC [34], the pore types in the deep-marine shale of the study area included H2, H3, and H4. The isothermal adsorption curve of Wufeng Formation shale (4105.15 m) was similar to that of  
Figure 2: SEM photomicrographs showing reservoir spaces of O\({}_{3}\)w–S\({}_{1}\)1 deep-marine shale. (**A**) Organic pores, Well A, Wufeng Formation, 4370.80 m; (**B**) abundant organic pores in bitumen, Well A, Section 1, 4364.66 m; (**C**) organic pores in bitumen, Well A, Section 2, 4376.68 m; (**D**) honeycomb organic pores, Well C, Section 3, 4081.23 m; (**E**) organic pores, Well A, Section 4, 4344.64 m; (**F**) intraparticle pores within calcite particles, Well B, Section 1, 3859.50 m; (**G**) interparticle pores between mineral particles, Well A, Section 4, 4344.64 m; (**H**) microfracture, Well D, Section 1, 4386.21 m; (**I**) microfracture in clay minerals, Well C, Section 2, 4095.13 m; (**J**) microfracture, Well A, Section 3, 4348.55 m; (**K**) microfracture, Well D, Section 4, 4236.88 m; (**L**) microfractures between mineral particles and organic matter, Well A, Section 4, 4355.08 m.  
the H3 type (Figure 3A). The curve shape of the adsorption stage became steeper near the saturated vapor pressure (SVP) point, indicating the large adsorption capacity contributed by abundant micro-nanopores. The desorption curve was gentle at the median pressure point, causing a wide hysteresis loop and suggesting that the pores were mainly parallel plate pores, which are conducive to the seepage migration of gas. The isothermal adsorption curve of Section 1 shale was similar to H2 morphology (Figure 3B). The curve shape of the adsorption stage became steeper at the SVP point, indicating that the adsorption capacity was large and that there were many micro-nanopores (Figure 3C). The desorption curve was steep near the median pressure point, causing a very wide hysteresis loop and suggesting that these pores were dominated by a cylindrical shape with open ends or fine-necked (ink-bottle-like) amorphous pores [37], which are beneficial to the adsorption and storage of natural gas. The adsorption isothermal curve of Section 2 shale was similar to that of H3 and H4 (Figure 3D). The adsorption curve was slower near the SVP point, reflecting that the adsorption content was small due to deficient micro-nanopores [37]. The desorption curve was gentle near the median pressure point, causing a narrow hysteresis loop and reflecting that the pores were mainly parallel-plate-like and slit-like amorphous pores (Figure 3E). The isothermal adsorption curve of Section 3 shale was similar to that of H2 (Figure 3F), and the adsorption curve became steeper at the SVP point, indicating that the adsorption capacity was large due to abundant micro-nanopores. The desorption curve was steeper near the median pressure point, causing a relatively wide and gentle hysteresis loop and suggesting that the pores were similar to those of Section 1 shale (Figure 3G), i.e., mainly cylindrical pores with open ends or fine-necked (ink-bottle-like) amorphous pores. The isothermal adsorption curve of Section 4 shale was similar to that of H4 and H3 (Figure 3H), and the adsorption curve became gentler at the SVP point, indicating that the adsorption capacity was small, which was caused by deficient micro-nanopores. The pores of Section 4 had both parallel-plate-like and slit-like pores, facilitating the migration of pore fluids (Figure 3I). The pore morphologies reflected by the hysteresis loops formed by the nitrogen adsorption-desorption curves were also confirmed with SEM images.  
Figure 3: _Cont._