## 4 Results
### Bound and Movable Fluids  
During oil and gas migration, a certain amount of water remains in the pore system, almost non-flowing, called bound water. Bound water is mostly distributed in the pores with pore sizes smaller than 200 nm, whose presence and distribution are significantly influenced by the solid properties. The corresponding saturation of bound water is called  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Sample** & **Depth (m)** & **Layer** & \
\begin{tabular}{c} **NMR** \\ **Porosity (\%)** \\ \end{tabular} &
\begin{tabular}{c} **Permeability** \\ **(mD)** \\ \end{tabular} & \(T_{\text{2C}}\) **(ms)** \\ \hline Q0 & 4110.7 & 1 & 2.61 & 0.00011 & 60.4400 \\ \hline Q1 & 4105.0 & \multirow{2}{*}{2} & 4.17 & 0.235 & 35.7905 \\ \cline{1-1} Q2 & 4101.2 & & 4.52 & 0.00030 & 16.3092 \\ \hline Q3 & 4096.1 & \multirow{2}{*}{3} & 3.42 & 0.00022 & 60.4400 \\ \cline{1-1} Q4 & 4091.4 & & 4.11 & 0.00053 & 68.8991 \\ \cline{1-1} Q5 & 4086.4 & & 5.95 & 0.0041 & 68.8991 \\ \cline{1-1} Q6 & 4081.7 & & 4.42 & 0.00069 & 60.4400 \\ \cline{1-1} Q7 & 4076.1 & & 3.16 & 0.00011 & 5.7190 \\ \cline{1-1} Q8 & 4071.3 & & 6.52 & 0.0046 & 2.9708 \\ \cline{1-1} Q9 & 4066.2 & & 4.67 & 0.00077 & 2.6061 \\ \cline{1-1} Q10 & 4061.7 & & 4.24 & 0.00066 & 2.9708 \\ \cline{1-1} Q11 & 4056.7 & & 3.86 & 0.00041 & 2.2861 \\ \cline{1-1} Q12 & 4051.9 & & 4.97 & 0.0011 & 2.9708 \\ \cline{1-1} Q13 & 4046.2 & & 3.85 & 0.00039 & 2.6061 \\ \cline{1-1} Q14 & 4042.2 & & 4.05 & 0.00044 & 2.6061 \\ \cline{1-1} Q15 & 4036.5 & & 4.81 & 0.0012 & 2.2861 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Porosity and permeability characteristics of representative samples from each layer of the Wufeng–Longmaxi Formation in the Z-3 well.  
Figure 3: Comparison of NMR pore size distributions of tested shale samples.  
bound water saturation. The saturation of movable fluids reflects the amount of fluid that can be collected and produced in a reservoir, which is of great significance for reservoir evaluation and exploitation.  
The bound water saturation of tested samples from the Z-3 well ranged from 26.41% to 92.2%, with an average value of 84.24% (Figure 4). The higher the saturation of the bound fluid, the more pores with sizes ranging from 1 nm to 200 nm developed in the sample. The pores with a pore size larger than 0.2 um are more developed, with higher saturation of the movable fluid, showing better flow capacity of the reservoir. The samples exhibit a relatively high bound water saturation, while the movable fluid saturation tends to be relatively low, which represents the high proportion of pores with a pore size of 1 nm-200 nm in the relaxation time of \(T_{2}\) spectrum distribution. Thus, pores with a pore size of less than 100 nm are more developed in the samples and composed of the major microstorage space. Note that the movable fluid saturation of Sample Q1 is much higher than the bound fluid saturation, indicating the unique pore structure.  
The \(T_{2}\) spectrum of the Q1 sample is characterized by a prolonged \(T_{2}\) relaxation time, with no distinct peak observed between pore sizes ranging from 1 nm to 20 nm, as well as between 20 nm and 100 nm (Figure 3). Moreover, the permeability of the Q1 sample is significantly better than the other layers. The significant difference between the saturation of movable fluid in Sample Q1 and other samples indicates that the high saturation of movable fluid contributes to favorable conditions for percolation. The enlarged pore size and improved connectivity promote the generation of sufficient storage space and efficient paths for fluid flow in the reservoir.