# A Study on the Remaining Reserves of the Weiyuan Shale Gas Block in Three-Dimensional Development
## 3 Evaluation of Remaining Reserves
### Calculation of Remaining Reserves  
The difference between the static geologic reserves and the total well control dynamic reserves in the Weiyuan block is taken as the remaining reserves in the Weiyuan block. Since the Weiyuan block has not been developed for large-scale production in the eastern and northwestern parts of the block, the scope of the calculation and the map of the abundance and EUR distribution of the geologic reserves in the Weiyuan block are limited to the main distribution area of the production wells (Figure 5), and the static geologic reserves, abundance, and well control dynamic geologic reserves and abundance within the main distribution area of the production wells are obtained by calculating the static geologic reserves, abundance, and well control dynamic geologic reserves and abundance in the Weiyuan block.  
Figure 4: A 3D trend diagram of dynamic well control reserves in the construction production area of the Weiyuan block. The vector arrow represents the distribution trend of well controlled reserves, pointing in the direction from high well controlled reserves to low well controlled reserves.  
Figure 3: Contour map of dynamic well control reserves in the Weiyuan area.  
According to the remaining reserves estimation principle, the total remaining geological reserves \(G_{r}\) are  
\[G_{r}=G_{z}-G_{d} \tag{1}\]  
where \(G_{z}\), total geological reserves, 10\({}^{8}\) m\({}^{3}\); \(G_{r}\), total remaining geological reserves, 10\({}^{8}\) m\({}^{3}\); \(G_{d}\), total well control dynamic reserves, 10\({}^{8}\) m\({}^{3}\).  
Based on statistics and calculations (Table 2), the total well control dynamic reserves in the main distribution area of the production wells are 906.7 \(\times\) 10\({}^{8}\) m\({}^{3}\) and the static geological reserves are 2519.9 \(\times\) 10\({}^{8}\) m\({}^{3}\). Thus, the total remaining geological reserves are found to be 1613.2 \(\times\) 10\({}^{8}\) m\({}^{3}\) according to Equation (1).  
According to the reserve abundance and well area control area distribution of the main production build-up area in the Weiyuan block, the statistics of the vertical remaining reserve data of typical wells (Table 3) show that horizontal wells can only exploit 35-60% of the static geological reserves, and there are 40-65% of the vertical remaining reserves that are undeveloped. The average remaining reserves of platform wells are (1.2-3) \(\times\) 10\({}^{8}\) m\({}^{3}\), with localized potential for exploration.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Reserve** & \multicolumn{2}{c}{**Average Reserve**} & **Area of Wells/(km\({}^{2}\))** & **Geological Reserves/(10\({}^{8}\)m\({}^{3}\))** \\
**Abundance/(10\({}^{8}\) m\({}^{3}\).km\({}^{-2}\))** & **Abundance/(10\({}^{8}\) m\({}^{3}\).km\({}^{-2}\))** & **Area of Wells/(km\({}^{2}\))** & 231.94 \\ \hline
3–4 & 3.61 & 64.25 & 231.94 \\
4–5 & 4.49 & 85.74 & 384.97 \\
5–6 & 5.52 & 79.54 & 439.06 \\
6–7 & 6.56 & 123.56 & 810.55 \\
7–8 & 7.44 & 87.82 & 653.38 \\ Aggregate & / & 440.91 & 2519.9 \\ \hline \hline \end{tabular}
\end{table}
Table 2: Static geological reserve statistics of major production areas in Weiyuan.  
Figure 5: Contour map of abundance plane in Weiyuan construction production area: (**a**) geological reserve abundance map; (**b**) semi-branched EUR abundance contour map; (**c**) well control reserve abundance map; (**d**) abundance map of remaining reserves.