## 5 Gas Extraction Process Optimization and Field Test Validation
### Analysis of Gas Extraction Processes
#### 5.1.2 Comparative Analysis of Economic Benefits  
According to the two preliminary extraction and depressurized gas extraction schemes mentioned in the previous section and after comparing the number of construction boreholes and the total drilling volume, it can be seen that the total number of directional long boreholes is 203 fewer than the total number of high-level oblique boreholes, and the total drilling volume is saved by 27,407 m. The use of directional long boreholes to extract decompressed gas significantly reduces the amount of drilling work and the cost of gas control, and also has significant advantages in terms of the amount of equipment, the number of construction personnel, the time required for construction, etc. A comparison of the economic benefits of specific high-level oblique boreholes and directional long boreholes is shown in Table 2.  
According to Table 2, in the gas extraction process using high-level oblique boreholes to unload the pressure, the unit price of borehole construction is 130 CNY/m and the construction cost is CNY 4,580,420. For the gas extraction process using directional long boreholes to unload the pressure, the unit price of borehole construction is 350 CNY/m and the construction cost is CNY 2,739,100. The economic cost-benefit ratio of using high-level oblique borehole and directional long boreholes to unload the gas extraction process is 1.67.  
From the comprehensive analysis of the gas extraction effect and economic benefits of the two processes, it can be determined that the directional long borehole extraction and depressurization gas extraction process has a better gas extraction effect, a higher borehole utilization rate, and a lower economic impact; it is therefore the preferred depressurization gas extraction process method for the 1504 working face in East 2 of Dalong Coal Mine.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Drilling Process**} & **Number of** & **Drill Rig** & \multirow{2}{*}{**Time (d)**} & **Unit Price** & \multirow{2}{*}{**Cost (CNY)**} \\  & **Boreholes/Total Number** & **Model/Number** & & **(CST)/Personnel** & \\ \hline high-level & & & & \\ oblique & 219/35,234 & ZDY-3500 LP/2/4 & 630 & 130 & 4,580,420 \\ boreholes & & & & & \\ directional long & 16/7826 & ZDY-12000 LD/1/2 & 200 & 350 & 2,739,100 \\ boreholes & & & & & \\ \hline \end{tabular}
\end{table}
Table 2: Comparison of the economic benefits of high-level oblique boreholes and directional long boreholes.  
From the data, the pure quantity of gas extracted for each directional long borehole was calculated and is shown in Figure 23. It can be concluded that the average gas extraction rate of the 1# directional long boreholes is 4.43 m\({}^{3}\)/min, and the average rate of pure gas extraction is 2.15 m\({}^{3}\)/min. The average gas extraction rate of 2# is 3.41 m\({}^{3}\)/min and the average rate of pure gas extraction is 1.87 m\({}^{3}\)/min. The 3# directional long boreholes have an average gas extraction rate of 3.74 m\({}^{3}\)/min and an average rate of pure gas extraction of 1.78 m\({}^{3}\)/min. The 4# directional long boreholes have an average gas extraction rate of 4.05 m\({}^{3}\)/min and an average rate of pure gas extraction of 1.63 m\({}^{3}\)/min.