## 4 Results and Discussion
### Pore Structure Quantitative Characteristics
#### 4.2.2 Pore Size Distribution  
Based on LTNA analyses, Section 1 shale had the largest pore volume, while Section 2 shale and Section 4 shale had the smallest pore volume. The pore size was mainly distributed in 1 nm-200 nm, and pores ranging between 4 nm and 30 nm composed the major part of the pore volume. The pores larger than 30 nm in Wufeng Formation Section 1 shale and Section 3 shale were the most developed (Figure 4).  
Figure 4: Pore size distribution with LTNA of the Wufeng–Longmaxi Formation deep-marine shale.  
Figure 3: LTNA curves of Wufeng–Longmaxi Formation deep-marine shale. **(A)** Well C, Wufeng Formation, 4105.15 m; **(B)** Well C, Section 1, 4100.96 m; **(C)** Well C, Section 1, 4101.57 m; **(D)** Well C, Section 2, 4085.45 m; **(E)** Well C, Section 2, 4092.13 m; **(F)** Well C, Section 3, 4084.05 m; **(G)** Well C, Section 3, 4078.23 m; **(H)** Well C, Section 4, 4067.88 m; **(I)** Well C, Section 4, 4062.9 m.  
NMR T\({}_{2}\) time is positively correlated with shale pore size, and spectral peak area is positively correlated with shale porosity [38]. The NMR T\({}_{2}\) spectral morphology can also reflect the pore size distribution and development degree in a shale reservoir. The NMR T\({}_{2}\) spectra of the deep-marine shale showed a bimodal or trimodal pattern, but the T\({}_{2}\) values corresponding to their main peaks were small, indicating that the pore volume of the deep-marine shale was mainly contributed by small pores. The T\({}_{2}\) value corresponding to the main peak of the NMR T\({}_{2}\) spectrum in Section 1 exceeded 1 ms, indicating a relatively large pore network (Figure 5).  
In order to quantitatively characterize the degree of pore development of different pore sizes more intuitively, the LTNA and NMR test results were fitted to calculate the optimal C value (Figure 6), thereby obtaining the pore size distribution on the basis of the NMR results.  
The results show that the pore size distribution in O\({}_{3}\)w and Section 1 shale was concentrated in 10 nm-100 nm, and the large pore size pores were more developed. The pore size distribution in Section 3 was concentrated between 5 nm and 50 nm, and the proportion of pores over 1000 nm was large (Figure 7). The pore size distribution within Section 2 was concentrated in 5 nm-50 nm, and the proportions of macropores and micropores were small. The pore size distribution in Section 4 was concentrated in 2 nm-50 nm, and the proportion of macropores was also small, but the proportion of micropores was relatively large.  
Figure 5: NMR T\({}_{2}\) spectra under different states for the deep-marine shale of the Wufeng–Longmaxi Formation. (**A**) Well A, Wufeng Formation, 4373.7 m; (**B**) Well A, Section 1, 4366 m; (**C**) Well A, Section 2, 4359.3 m; (**D**) Well B, Section 3, 4024.92 m; (**E**) Well A, Section 4, 4354.71 m.  
Figure 6: Fitting relationship between NMR T\({}_{2}\) spectra and LTNA for the O\({}_{3}\)w–S\({}_{1}\)1 deep-marine shale. (**A**) Fitting process diagram of NMR T\({}_{2}\) spectra and LTNA; (**B**) Fitting result of NMR T\({}_{2}\) spectra and LTNA.  
Figure 7: Pore size distribution of the O\({}_{3}\)w–S\({}_{1}\)1 deep-marine shale. (**A**) Well A, Wufeng Formation, 4373.7 m; (**B**) Well A, Section 1, 4366 m; (**C**) Well A, Section 2, 4363.05 m; (**D**) Well A, Section 3, 4355.3 m; (**E**) Well A, Section 4, 4341.3 m.