To accurately determine the effective extraction radius of directional long drilling, the influence of the negative pressure of the hole mouth, the drilling diameter, and the drilling length of the hole on the effective extraction radius of a directional long drilling hole is simulated by establishing a coal-to-gas gas-structure coupling model considering the Klinkenberg effect. Finally, the reliability of the numerical simulation is verified through field testing in Yuxi Coal Mine. The results reveal that the attenuation of negative pressure in a directional long borehole along a long hole has a significant influence on the gas extraction effect. The radial gas pressure of the extraction drilling hole is distributed in a “V” shape when the negative pressure of the extraction decays along the direction of the hole length. The higher the negative pressure and the longer the diameter of the drilling hole, the higher is the gas extraction effect. The effective extraction radius is exponentially related to the drilled hole depth when the negative pressure of extraction is attenuated along the long hole direction. The negative pressure of the hole and the diameter of the borehole are linearly related to the effective extraction radius at the depth of drilling hole of 430 m. Through field tests, while extracting for 180 days based on the stubble pressing effect, the effective extraction radius of the directional long borehole of the No. 3 coal seam of Yuxi Coal Mine is 5.7 m, and the absolute error between the numerical simulation is 0.1 m. In addition, the gas pressure obtained from different sampling points is consistent with the numerical simulation. The relative error is 0.3–4.1%. The results provide a theoretical basis for the rational layout of directional drilling.

A proper understanding of the change characteristics of negative drainage pressure along a drilling hole is essential since gas drainage parameters are the key parameters that influence the efficiency of gas drainage. In this study, based on the coupling of gas seepage from coal seams and the gas flow along the drilling hole, a theoretical model was established to calculate the gas pressure change law along the drilling hole with different influencing factors. Subsequently, a multibranch method was applied to test the negative pressure at different drilling holes. Finally, a field test was conducted in the Jiulishan coal mine to analyze the changed characteristics of the negative drainage pressure along the drilling hole. The results show that at a constant negative drainage pressure in the borehole, the negative pressure gradually decreased with increasing depth. With an increase in negative drainage pressure at the borehole, the negative pressure loss for every 100 m substantially increased. The gas flux had the most obvious influence on the negative pressure in the drilling hole, and the pressure loss rapidly increased with increasing gas flux. When the diameter of the borehole was small, the negative pressure loss was significant; when the drilling hole was deep, the negative pressure decreased more significantly. This study has important theoretical and practical significance for improving the gas drainage effect.