针对煤矿井下密闭取样无心钻进长度难以确定这一难题，分析钻孔孔底煤层瓦斯涌出规律，建立流−固耦合模型，模拟分析煤层初始渗透率、煤层初始瓦斯压力、钻孔直径、煤壁暴露时间对钻孔孔底 煤层瓦斯排放带长度的影响；拟合得出钻孔孔底煤层瓦斯排放带长度预测方程。结果表明：在不同的排放时间段内，钻孔孔底煤层瓦斯排放带内煤层瓦斯压力均为先快速增长、后趋于稳定；在同一煤层条件下，煤壁暴露时间越长，形成钻孔孔底煤层瓦斯排放带长度越长；煤层初始瓦斯压力是影响钻孔孔底煤层瓦斯排放带长度的重要因素；钻孔直径的增大能够使更远处的瓦斯进行排放，使钻孔孔底煤层瓦斯排放带的长度增加；煤层初始渗透率增大能够影响钻孔孔底煤层瓦斯排放带长度增长，但煤层内的瓦斯量为定值，因此钻孔孔底煤层瓦斯排放带的长度有极限值；采用偏最小二乘法分析得出的对钻孔孔底煤层瓦斯排放带长度影响程度从强到弱依次为煤层初始瓦斯压力、煤壁暴露时间、煤层初始渗透率、钻孔直径。

Aiming at the problem that it is difficult to determine the length of coreless drilling in underground coal mine, in order to explore the length of gas emission zone in coal seam at the bottom of borehole, the gas emission law of coal seam at the bottom of borehole is analyzed, and the fluid-solid coupling model is established. The influence of initial permeability of coal seam, initial gas pressure of coal seam, borehole diameter and exposure time of coal wall on the length of gas emission zone in coal seam at the bottom of borehole is simulated and analyzed; the prediction equation of the length of the gas emission zone at the bottom of the borehole is obtained by fitting. The results show that in different emission time periods, the coal seam gas pressure in the coal seam gas emission zone at the bottom of the borehole increases rapidly at first and then tends to be stable. Under the condition of the same coal seam, the longer the exposure time of the coal wall, the longer the length of the coal seam gas emission zone formed at the bottom of the borehole; the initial gas pressure of coal seam is an important factor affecting the length of gas discharge zone at the bottom of borehole. The increase of the diameter of the borehole can make the gas discharge farther away, and increase the length of the coal seam gas discharge zone at the bottom of the borehole. The increase of the initial permeability of the coal seam can affect the growth of the length of the coal seam gas emission zone at the bottom of the borehole, but the amount of gas in the coal seam is a fixed value, so the length of the coal seam gas emission zone at the bottom of the borehole has a limit value. Analyze the influence degree by the partial least squares method of the length of the coal seam gas discharge zone at the bottom of the borehole from strong to weak is the initial gas pressure of the coal seam, the exposure time of the coal wall, the initial permeability of the coal seam and the diameter of the borehole.