## 5 Engineering Application
### Panxie Coal Mine of Huainan Mine Area  
In order to address the low efficiency of gas drainage and the tight mining schedule in the Panxie coal mine, a set of U-shaped wells was constructed above the 13,015 working face at a distance of 80 m from the return airway. The horizontal section of well XX-1L had a length of 1066 m, which was divided into 12 segments for hydraulic fracturing. The spacing between each segment ranged from 62 to 150 m. Each segment was perforated once, and the average injection rate for hydraulic fracturing was approximately 7.5 m\({}^{3}\)/min. The average proppant volume per segment was 45 m\({}^{3}\), and the average fracturing fluid injection volume per segment was 916 m\({}^{3}\). The total proppant volume was 534 m\({}^{3}\), and the total fracturing fluid volume was 10,996 m\({}^{3}\). The average proppant concentration for each segment ranged from 6.7% to 11.6%, with average injection rates between 5.7 and 8.2 m\({}^{3}\)/min. The maximum construction fracturing pressure was 63.9 MPa, the minimum was 40.1 MPa, and the construction pressure generally ranged from 22.4 to 47.6 MPa. The fracturing construction parameters are shown in Table 4.  
During the hydraulic fracturing construction process, the morphology of the fractures in the horizontal wells was monitored using microseismic fracture monitoring technology. The monitoring results of the microseismic fracture length are shown in Table 5. The total length of the main fractures ranged from approximately 191.5 to 218.3 m, with a general orientation towards the northeast. These fractures were able to propagate into the coal seam, as demonstrated in Figure 15. The height of the fractures ranged from approximately  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Section Sequence**} & \multicolumn{2}{c}{**Hydraulic**} & \multirow{2}{*}{**Sand Total/m\({}^{3}\)**} & \multirow{2}{*}{**Average Pump**} & \multirow{2}{*}{**Average Sand**} & \multirow{2}{*}{**Average**} \\  & **Fracturing** & & & & **Pressure/MPa** & \\  & **Liquid Volume/m\({}^{3}\)** & & & & \\ \hline
1 & 1131 & 35.0 & 22.4 & 6.7 & 7.3 \\
2 & 1001 & 45.1 & 33.4 & 8.2 & 8.2 \\
3 & 967 & 45.5 & 39.3 & 8.4 & 8.0 \\
4 & 1011 & 55.2 & 44.7 & 9.2 & 5.7 \\
5 &  
30.0 to 36.8 m, completely covering the thickness range of the coal seam, as shown in Figure 16. This confirmed that the fractures in the roof strata can penetrate into the coal seam and propagate over a considerable distance within the coal seam and the roof strata, achieving the goal of enhancing the coal seam.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Section** & **Orientation/\({}^{\circ}\)** & **Total Fracture** & **East Wing** & **West Wing** & & \\
**Sequence** & **Orientation/\({}^{\circ}\)** & **Total Fracture** & **Fracture** & **Fracture** & **Height/m** & **Inclination Angle/\({}^{\circ}\)** \\ \hline
3 & 71.7 & 205.1 & 112.2 & 92.9 & 31.5 & 3 \\
6 & 74.9 & 197.7 & 108.2 & 89.5 & 30.0 & 5 \\
7 & 80.6 & 191.5 & 92.9 & 98.6 & 36.8 & 3 \\
11 & 77.9 & 218.3 & 104.8 & 113.5 & 36.8 & 1 \\ \hline \hline \end{tabular}
\end{table}
Table 5: Statistical table of microseismic monitoring for fracture lengths in XX-1L horizontal well.  
Figure 15: Fracture orientation and length of XX-1L well.  
XX-1L well group was in operation for a total of 671 days. During this period, gas production was suspended for 11 days from 8 May 2020, to 18 May 2020, due to excessive coal powder deposition, which required coal powder treatment. Currently, the XX-1L well produces 493 cubic meters of gas and 7.9 cubic meters of water daily. The maximum daily natural gas production from the XX-1L horizontal well reached 1450 cubic meters. Cumulative gas production amounted to 43.62 \(\times\) 10\({}^{4}\) cubic meters, while cumulative water production stood at 1.19 \(\times\) 10\({}^{4}\) cubic meters, as shown in Figure 17.  
Figure 16: Profile of microseismic monitoring for fractures in XX-1L well.