Protected seam bottom plate upward comb-shaped drilled hole gas extraction method

[0017] Such as figure 1 As shown, the comb-shaped borehole gas drainage method of the bottom plate of the protected layer of the present invention firstly arranges the drill site A in the bottom plate III of the protected layer, and first drills a main hole 1 in the drill site A along the direction of the working face. 1 The vertical distance between the horizontal position and the protected layer Ⅱ is 15-25m; after the main hole 1 is drilled 15m, stop drilling, ream the main hole 1, install the sealing pipe in the reaming hole, and install the sealing pipe The length of the hole is 8~15m; install the blowout preventer and the gas-water separator at the orifice; continue to drill the main hole 1 along the direction of the working face with near-horizontal directional drilling until the main hole 1 reaches the set depth; built into the main hole 1 Enter the packer whipstock 3 to the innermost end, and then set the position of the first strong manufacturing bevel point from the inside to the outside, and use the small diameter and large angle hole bottom motor 4 for bevel drilling to keep the drilling track to a minimum The radius extends to 0.5m through the protected layer II into the top plate I of the protected layer, completing the first branch hole 2; exit the hole bottom motor 4 from the first branch hole 2, and move the packer whipstock 3 outward to At the next strong manufacturing oblique point position, the next branch hole 2 is drilled by the hole bottom motor 4, and the drilling of all the branch holes 2 with the strong manufacturing oblique point position is completed from the inside to the outside, and finally a set is formed The multi-branch comb-shaped boreholes distributed in the bottom plate III of the protected layer, the spacing between the multi-branch comb-shaped boreholes is 20-30m; the negative pressure for gas drainage of the multi-branch comb-shaped borehole is 25-40kPa; Install a gas drainage pipeline at the orifice of the main hole 1.

[0018] Repeat the above steps to complete multiple sets of multi-branch comb drill holes distributed in the bottom plate III of the protected layer within the scope of the protected layer II, and install gas drainage pipelines at the orifices of the main holes 1 of each group. A group of multi-branch comb-shaped boreholes distributed in the bottom plate III of the protected layer are formed for gas drainage.

[0019] This method can pre-drain the gas in the protected layer before the mining of the protective layer. As the mining face advances during the mining of the protective layer, the protected layer will loosen and produce pressure relief and permeability enhancement effects, and a large amount of pressure will be relieved under the action of negative pressure in drainage The gas enters the comb borehole and is pumped out through the drainage pipeline.