Numerical simulation of coal seam gas emission zone at the bottom of sampling borehole

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.