# Experimental Study on High-Energy Gas Fracturing Artificial Coal
## 3 High-Energy Gas Fracturing Test
### Test Method  
Based on the experimental results in the literature [26], cement, sand, and water are selected as the basic materials to control the structural strength of the simulated coal; gypsum, perlite, foaming agent, and crushed mica are selected as additives to control the microcracks, microporous, structural surfaces, and gases in the simulated coal. The materials, proportions, and basic physical and mechanical parameters of the simulated coal are shown in Table 4.  
To verify the reasonableness of the present simulated material, some basic mechanical parameters of the real coal from Jiaozuo Zhongma Mine are given in Table 5[27]. Comparing Tables 4 and 5, it can be seen that the strength, Poisson's ratio, and Young's modulus of the present simulated material are less different from those of the real coal, so the simulated coal sample can be used to study the mechanism of high-energy gas fracture coal body. The test block size is 1000 mm \(\times\) 1000 mm \(\times\) 600 mm, mixed manually and compacted with a small vibrating plate in the mold and maintained for 28 days (shown in Figure 1a). In the middle of the test block, a borehole of 50 mm in diameter and 400 mm in depth is left in advance. After putting the fracturing agent charge roll into the borehole, the borehole is sealed with Bar glue. When ready, use the ignition device to excite the fracturing agent. The fracturing agent and ignition device are shown in Figure 1b,c. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Materials and Proportioning** & **Density** & **Poisson’s** & **Compressive** & **Longitudinal** & **Young’s** \\ \hline
**Sand:Water:Cement:Gypsum:Crushed** & **\(\rho\) (g/cm\({}^{3}\))** & **Ratio, \(\mu\)** & **Strength \(\sigma_{e}\)/MPa** & **Wave Velocity** & **Modulus** \\
**Mica:Perlite:Foaming Agent** & & & & **E/GPa** \\ \hline
4.346:0.501:1.581:0.327:0.035:0.023:0.067 & 1.84 & 0.18 & 24.25 & 2580 & 4.73 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Materials, proportions, and basic physical and mechanical parameters of the simulated coal. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Test Project** & **Test Conditions** & **Test Results** \\ \hline Friction Sensitivity Test/\% & Temperature: 20 \({}^{\circ}\)C; Humidity: 55\% & 8\% \\  & Pendulum angles: 66\({}^{\circ}\); Pressure: 2.5 MPa & 8\% \\  & Temperature: 20 \({}^{\circ}\)C; Humidity: 59\% & 10\% \\  & Hammer weight: 10.0 kg & 120 \\ Pressure resistance test/(MPa) & & 163 \\ Temperature resistance test & & \\ (\({}^{\circ}\)C/48 h) & & \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Fracturing agent sensitivity, pressure, and temperature resistance test results. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Coal Sample Name** & **Compressive Strength \(\sigma_{e}\)/MPa** & **Young’s Modulus E/GPa** & **Poisson’s Ratio, \(\mu\)** \\ \hline Jiaozuo Zhongma Coal Mine No.2 & 28.735 & 4.054 & 0.245 \\ Jiaozuo Zhongma Coal Mine No.2 & 37.512 & 3.883 & 0.184 \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Basic mechanical parameters of coal. The borehole wall pressure test is realized by pasting a pressure sensor on the borehole wall. The pressure sensor is glued to the borehole wall with 502 glue, and then the signal line is connected to the signal acquisition system through the orifice. When the high-energy gas acts on the borehole wall, the sensor is squeezed to generate electrical signals, which are transmitted to the signal acquisition system through the charge amplifier to realize the acquisition of the pressure-time curve. The pressure sensor used in this test was a PVDF piezoelectric sensor (Figure 2a), and the signal acquisition system was the DH5922N dynamic strain gauge. (Figure 2b), which was set at 200 kHz of collection frequency. The arrangement of the measurement points for the borehole wall pressure test is shown in Figure 2c. The strain brick is shown in Figure 3a and has a size of 20 mm \(\times\) 20 mm \(\times\) 20 mm, and its material and proportion are the same as the test block.