Abstract
Aiming at the difficulty of gas drainage by drilling along the seam in soft coal seam, the permeability of coal seam was increased by hydraulic fracturing test in the field, and the permeability and gas drainage parameters of coal seam before and after fracturing were studied. The results show that: ① The fracture initiation pressure of 3# coal seam in Guojiahe coal mine is 15~20MPa. When the water injection is 30~40m3, the fracturing radius is 15m, when the water injection is 50 ~ 60m3, the fracturing radius can reach 20m, when the water injection reaches 70m3, the fracturing radius can reach 30m; ② Driven by high pressure water, the gas in the fractured area migrates to the unfractured area, and the gas content in the fractured area decreases; ③ The attenuation coefficient of natural gas flow after fracturing is reduced by 50% compared with that before fracturing, and the permeability coefficient of coal seam after fracturing is increased by 50 times compared with that of original area; ④ The recovery concentration after fracturing is much higher than that before fracturing.
Highlights
Coalbed methane (CBM) can effectively develop and utilize coal resources to reduce the hidden danger of major gas disasters in coal mines, turn greenhouse gases into treasure and increase the share of energy selfsufficiency
The 1307 working face is located at +820m level in Guojiahe coal mine
The drilling parameters and gas content in the original area are shown in table 1, because of the driving effect of high-pressure water, the gas in the fractured area migrates to the unfractured area, and the gas content in the fractured area decreases
Summary
The 1307 working face is located at +820m level in Guojiahe coal mine. The coal seam is 3# coal seam with an average thickness of 16m. The coal seam contains 1~2 layers of gangue, with a thickness of 0.2~0.5m. It is estimated that the original gas content of the coal seam in the working face is 3~4m3/t. The 3# coal seam of the working face is black, and the coal petrology type is mainly semi dark type. The upper 3m and the lower 2m are semi bright briquette. The coal petrographic composition is mainly dark coal and bright coal, with local pyrite film, brown black stripes and uneven fracture. The upper and lower semi bright briquettes are layered structure, and the middle part is massive structure, strip structure and asphalt luster. The gangue is mudstone, and there is about 1 meter thick inferior coal in some areas
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