Study on gas extraction characteristics of multi-branch directional long drillings along underground coal seam

The characteristics of "ultra-deep hole, incidental branch" of directional drilling along underground coal seam make the gas drainage characteristics different from those of ordinary drilling.Firstly, the variation characteristics of the effective influence range of the pre-drainage borehole in the test mine with time were analyzed by numerical simulation.Then combined with the actual mine to determine the test directional drilling arrangement spacing of 5 m.Two groups of experimental directional drilling groups with fan-shaped arrangement of 1 branch and 2 branches were set up and the pure quantity of drainage was measured.The measured results show that the pure quantity of drainage by directional drilling shows a trend of rapid decrease-fast increase-slow attenuation with time.The extraction stage can be divided into "U" type fluctuation period and stable attenuation period.In the two stages, the pure quantity and time of gas drainage respectively conform to the cubic polynomial relationship and the negative exponential function relationship.By comparing the predicted results with the measured results, it is found that the total amount of directional drilling extraction and residual gas content predicted by the "U" type model are more accurate than the negative exponential decay model.It is more suitable for the prediction of the gas drainage effect of directional drilling and engineering design.