# Optimization and Application of Drilling Parameters Based on Gas-Solid Coupling Simulation
## 6 Conclusions  
By establishing a gas-solid coupling model for gas drainage and employing COMSOL numerical simulation software, this study investigates the impacts of extraction negative pressure, borehole diameter, and extraction duration on coal seam gas pressure. Field validations were conducted, yielding the following conclusions:  
(1) By analyzing the change in gas pressure and effective extraction radius around the drill hole using the three influencing factors of different drill hole diameters, extraction times, and negative pressures, we came up with the optimal drill hole arrangement parameters: drill hole diameter of 203 mm, negative pressure of 25 kPa, and extraction time of 90 d.  
(2) The optimal drilling arrangement parameters obtained from the numerical simulation results are used to verify the extraction effect in the Fengtai coal mine through 80 days of observation and data recording of the pure volume of gas extraction, mixing volume, the upper corner, and the concentration of gas in the return airflow: the mixing volume of the directional high-level long boreholes ranged from 16.50 m\({}^{3}\)/min to 24.21 m\({}^{3}\)/min, and the pure volume of the extraction ranged from 0.93 m\({}^{3}\)/min to 11.14 m\({}^{3}\)/min; the gas concentration in the upper corner ranged from 0.14% to 0.25%, and the gas concentration in the return airflow ranged from 0.03% to 0.10%. The gas concentration in the upper corner \begin{table}
\begin{tabular}{c c c} \hline \hline
**Technology Type** & \
\begin{tabular}{c} **Directional High-Level** \\ **Long Boreholes** \\ \end{tabular} &
\begin{tabular}{c} **High-Level Drainage** \\ **Galleries** \\ \end{tabular} \\ \hline Roadway section area/m\({}^{2}\) & & 5.5 \\ Quantity of work/m & 1349 & 300 \\ Project unit price/CNY & 749.86 & 8000 \\ Total project price/CNY & 1,011,600 & 2,400,000 \\ Amount of gangue/ton & & 2733.5 \\ Gangue treatment cost/CNY & & 218,680 \\ Construction period/d & 15 & 84 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Comparative analysis of technical advantages. was between 0.14% and 0.25%, and the gas concentration in the return airflow was between 0.03% and 0.10%. The gas limit in the 15101 face was not exceeded, which further verified the rationality of the drilling parameters. (3) Adopting directional high-level long boreholes instead of high-level drainage galleries for gas extraction can reduce the construction cost by 69.42%, reduce the amount of gangue by 2733.5 tons, reduce the cost of gangue transportation by 218,680 CNY, and reduce the construction time by 82.14%. Deficiencies in the current research are as follows:  
(1) The gas-solid coupling model fails to consider temperature variations' impacts on gas adsorption-desorption behavior. In practical coal mining scenarios, dynamic temperature fluctuations during extraction activities may influence gas migration patterns. (2) The adoption of a two-dimensional planar model overlooks the effects of vertical permeability and three-dimensional fracture network distribution on gas drainage efficiency. (3) Field validations were exclusively conducted in a single mine (Fengtai Coal Mine), lacking verification in complex geological conditions (e.g., high tectonic stress zones, multi-fault coal seams), thereby limiting the universal applicability of the research findings. (4) There was a failure to place drill holes that effectively detect gas pressure to validate the rationality of the model  
Future research directions are as follows:  
(1) Develop a three-dimensional gas-solid coupling model incorporating heterogeneous coal masses, large deformation theory, temperature fields, dynamic permeability, and geological structures to enhance numerical simulation authenticity for gas drainage. (2) Validate model rationality in mines featuring multiple faults, high geothermal gradients, and intense tectonic stresses while investigating correction requirements for optimal borehole parameters under diverse geological conditions.