## 3 Result and Discussion
### Comparative Analysis of Sandstone Pore Throat Distributions  
Using the conversion coefficients C and n and Equation (6), the transverse relaxation time T\({}_{2}\) was converted into a pore size distribution. As illustrated, for core S1-1, a comparison chart of the pore throat distribution derived from the Tuha sandstone's NMR T\({}_{2}\) relaxation time distribution spectrum and the MICP pore throat distribution was constructed, as depicted in Figure 8.  
From Figure 8, it can be observed that the signal frequency curves of pore size distribution converted from both MICP and NMR do not align perfectly. Comparing the two methods, it is noticeable that the NMR-detected signal frequency is higher than that of the MICP method for pores smaller than 0.0037 \(\upmu\)m (micropores). This discrepancy is attributed to the sandstone mercury injection pressure set at 200 MPa, which is incapable of detecting pores smaller than 0.0037 \(\upmu\)m. However, NMR can detect all hydrogen-containing \begin{table}
\begin{tabular}{c c c c c c} \hline
**Well Number** & **Samples** & **Saturation of MICP (\%)** & **C** & **n** & **R\({}^{2}\)** \\ \hline \multirow{4}{*}{S1} & 1 & 93.194 & 0.0197 & 1.0121 & 0.9059 \\  & 2 & 85.503 & 0.0112 & 0.8718 & 0.9951 \\  & 3 & 78.665 & 0.0129 & 0.7945 & 0.9950 \\  & 4 & 81.174 & 0.0179 & 0.8916 & 0.9878 \\ \hline \multirow{2}{*}{S2} & 5 & 92.531 & 0.0261 & 1.0490 & 0.9475 \\  & 6 & 88.878 & 0.0231 & 1.0635 & 0.9498 \\ \hline \multirow{2}{*}{S3} & 7 & 89.929 & 0.0179 & 0.9565 & 0.9157 \\  & 8 & 92.171 & 0.0213 & 1.0685 & 0.9447 \\ \hline \multirow{2}{*}{H1} & 1 & 94.802 & 0.0281 & 1.3238 & 0.8993 \\  & 2 & 93.544 & 0.0245 & 1.4426 & 0.8858 \\ \hline \multirow{2}{*}{H2} & 3 & 59.246 & 0.0192 & 1.3348 & 0.8872 \\  & 4 & 79.073 & 0.0204 & 1.3472 & 0.9088 \\ \hline \multirow{2}{*}{H3} & 5 & 83.450 & 0.0086 & 1.0868 & 0.8859 \\  & 6 & 89.400 & 0.0173 & 1.2396 & 0.8662 \\ \hline \multirow{2}{*}{H4} & 7 & 83.649 & 0.0227 & 1.3416 & 0.8995 \\  & 8 & 75.774 & 0.0207 & 1.2822 & 0.8448 \\ \hline \end{tabular}
\end{table} 
Table 3: Conversion factors between NMR T\({}_{2}\) relaxation time distribution spectrum and pore throat radius and correlation index. Figure 7: Fitting-related parameters of conversion from NMR T\({}_{2}\) to pore radius (S1-1 and H3-5). fluid volumes in the rock sample; hence, for pores smaller than 0.0037 \(\upmu\)m, the distribution frequency detected using NMR is higher than MICP. In the pore throat radius range of 0.0037-0.2 \(\upmu\)m, while the distribution frequency of the NMR signal mostly agrees with that of MICP, the discrepancy between the two methods increases with decreasing pore throat radius. This is likely due to the inability of mercury intrusion to access some of the smaller and non-connected pores. In region 1 (0.2-1.8 \(\upmu\)m), the distribution frequency from MICP is notably higher than NMR, whereas in region 2 (1.8-7 \(\upmu\)m), it is lower than NMR. This divergence is due to the inherent differences in the two detection methods. When the core is fully saturated, the NMR T\({}_{2}\) relaxation time distribution spectrum distribution only reflects the distribution of pore size and pore throats in the rock sample. The intensity of the NMR signal represents the proportions of differently sized pores, uninfluenced by the connectivity of pores and throats. In contrast, the MICP method calculates the frequency distribution based on the volume of mercury that enters the rock sample at a specific injection pressure. For homogeneous rock samples, the MICP method yields accurate pore throat results. During the formation of reservoirs, depositional environments, diagenesis, tectonic actions, fluid activities, formation temperature, and pressure all have significant impacts on rock pore structures [3]. Due to the complex nature of stratification, especially in heterogeneous reservoirs where large pores connect with small throats, discrepancies arise, as shown in Figure 9.  
In Figure 9a, the pore throat radii are in the order \(r_{1}>r_{2}>r_{3}\).