Study On Gas Seepage Characteristics Of Coal Under High Pressure Water Jet

The geological conditions in our country are complex and the form of coal mine safety is grim.Due to the increase of mechanization degree and the increase of mining scale,the depletion of shallow resources in old mines leads to the extension of the exploitation depth of old mines.And the new wells can only extend to the deep coal seam and the gas content and pressure in the coal seam increase gradually.The technology is more complicated.There are two characteristics of the sudden accident.First the coal seam is gradually upgraded to the prominent coal seam.In the absence of sufficient defensive measures,the accident will happen.Second the original coal and gas outburst seam,due to the implementation of the corresponding defensive measures is not strong or not suitable for special geological conditions caused by accidents.Based on the summary of coal gas seepage equation,the gas seepage equation of high pressure water jet after coal is put forward.It can be concluded that different coal seams have different degrees of metamorphism and different porosities.Under the action of high pressure water,the pore structure of coal seams develops here,increasing the gas flow path in the coal seam and increasing the gas permeability.Under the condition of fixed pressure,the permeability of gas in the media shows a state of first decreasing and then increasing with the increase of pore pressure.During this period,the pore pressure has a turning point.In a fixed under the condition of confining pressure,coal gas permeability decreases as the pore pressure in the reflect a rise after falling first state,pore pressure during this period there was a turning point,the gas permeability curve on both sides of the turning point in the basic symmetry,into “U” glyph change.The gas permeability curve is in the range of the confining pressure increases,the gas permeability in the coal seam becomes smaller.After entering the coal body,water will occupy the percolation and migration channels,increasing the resistance of gas flow and reducing the permeability,at this point,the moisture on the coal gas seepage flow will produce a reaction,which is obstructing the water seepage on the gas side.However,after the high pressure water is injected into the coal seam,the pressure of water redevelops the cracks in the coal body and increases the permeability of the coal gas.The permeability of the gas increases.Compared with the permeability of the coal body,the influence of water can be ignored.