Abstract
Gas extraction cycle is too long in low‐permeability coal seam. In order to solve the problem, the basic principle about gas drainage drilling for gas injection technology is studied to increase permeability. And the mathematical model is established. Gas is injected into the low‐permeability coal seam by numerical simulation. The results indicate that the best condition is a negative pressure drainage at 26 kPa and a gas injection pressure at 0.6 MPa in the vertical direction and in the horizontal direction of the injection hole. In Shanxi Daping Coal Mine 3113 working face, the field test is implemented. As a result, the test is successful. During the 14 d gas injection constantly, gas content of coal seam is reduced from 12.33 m3/t to 7.12 m3/t, greatly reducing the risk of coal and gas outburst elimination time required.
Highlights
At present, the overall situation of gas extraction in China is bad, mainly because of the low-permeability of coal seam [1]
Gas injection technology for permeability enhancement is a new type of permeability increasing technology, which could increase the permeability of coal seam effectively [4]
E technology of gas injection and permeability enhancement has been developed from the field of coal bed methane development
Summary
The overall situation of gas extraction in China is bad, mainly because of the low-permeability of coal seam [1]. Field tests were successfully carried out [10,11,12], such as gas injection to eliminate outburst danger and gas injection to promote gas drainage, and certain effect was achieved. After N2 injection into the coal seam, partial pressure of CH4 is reduced to produce the competitive adsorption of multiple gases. In these three aspects, N2 completed the displacement of CH4 to have increased permeability of coal seam. Because the proportion of N2 in air accounts for 79.8% and it is very convenient to obtain compressed air under the mine, the air injection is selected to enhance the permeability. erefore, the numerical simulation process uses air as the simulation condition, and the compressed air in the compressed air system is taken as the gas source to conduct the field gas injection permeability enhancement test
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