# Optimization and Application of Drilling Parameters Based on Gas-Solid Coupling Simulation
## 4 Analysis of Numerical Simulation Results
### Analysis of the Effect of Negative Extraction Pressure on Gas Pressure  
The simulated working conditions are as follows: the initial gas pressure is 1 Mpa: the negative pressure of extraction is set to 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, and 35 kPa; the diameter of the borehole is 120 mm; and the extraction time is 50 d.  
Figure 2 shows the cloud diagram of gas pressure change in the coal body around the drill hole when the negative pressure of extraction is 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, and 35 kPa, respectively. According to the analysis of Figure 2, when extracting the gas from the coal body, due to the existence of the pressure difference between the negative pressure of extraction and the gas pressure of the coal seam, the gas pressure of the coal body around the drill hole decreases more, and the gas pressure of the coal body far away from the drill hole decreases slightly but is basically equal to the initial gas pressure of the coal seam. The gas pressure is slightly decreased but basically equal to the initial gas pressure of the coal seam, and the gas pressure is basically negatively correlated with the negative pressure of extraction. Figure 3 shows the variation in effective extraction radius at different extraction negative pressures (10 kPa, 15 kPa, 20 kPa, 20 kPa, 25 kPa, 30 kPa) and at different extraction times (30 d, 50 d, 70 d), and Table 2 shows the variation in effective extraction radius under different extraction times. According to Figure 3 and Table 2, it can be seen that the effective extraction radius changes in the range of 1.39 m-1.55 m, 1.96 m-2.40 m, and 2.87 m-4.38 m under the extraction times of 30 d, 50 d, and 70 d, corresponding to the negative pressures of 10 kPa, 15 kPa, 20 kPa, 25 kPa, 30 kPa, and 35 kPa respectively, and the effective extraction radius changes in the range of 1.39 m-1.55 m, 1.96 m-2.40 m, and 2.87 m-4.38 m, respectively, when the extraction time is the same; the higher the negative pressure of extraction, the larger the effective extraction radius is. When the extraction time is the same, the higher the negative pressure, the larger the effective extraction radius, but with the increasing negative pressure, the effective extraction radius increases, but when the negative pressure increases to a certain critical value, the effective extraction radius rate decreases significantly. \begin{table}
\begin{tabular}{c c c} \hline
**Parameters** & **Numerical Value** & **Parameter Unit** \\ \hline Klinkenberg factor & \(1.44\times 10^{5}\) & Pa \\ Molecular mass of methane gas & 16 & g/mol \\ Gas state constant & 8.413510 & J/mol/K \\ Seam temperature & 293 & K \\ Methane kinetic viscosity coefficient & \(1.08\times 10^{-5}\) & mu \\ Langmuir constant (limiting adsorption capacity) & 0.02 & m\({}^{3}\)/kg \\ Langmuir constant (pressure) & 3.03 & MPa \\ Molar volume of methane at standard conditions & 22.4 & L/mol \\ Apparent density of coal & 1.41 & kg/m\({}^{3}\) \\ Poisson’s ratio of coal & 0.3 & GPa \\ Limiting adsorption deformation & 0.005 & \\ Modulus of elasticity of coal matrix & 8200 & MPa \\ Modulus of elasticity of coal & 2800 & MPa \\ \hline \end{tabular}
\end{table} 
Table 1: _Cont._Figure 3: Variation in effective extraction radius with different extraction times. Figure 2: Gas pressure cloud under different negative pressure of extraction: (**a**) 10 kPa, (**b**) 15 kPa, (**c**) 20 kPa, (**d**) 25 kPa, (**e**) 30 kPa, (**f**) 35 kPa. At a certain extraction time, when the negative extraction pressure varies between 10 kPa and 25 kPa, the faster the rate of gas pressure decrease around the borehole, the more obvious the growth rate of the effective extraction radius, but after the negative extraction pressure is greater than 25 kPa, with the increase in negative extraction pressure, the rate of gas pressure decreases, and the growth rate of the effective extraction radius decreases significantly.