Study on long-distance fixed-point sealed coring technology in broken-soft coal seam

With the rapid development of mining, drilling and other technologies in the field of coal mine and the increasing demand for enhancing production and profit in the coal mine, the demand is increasingly urgent for detection of coal seam gas content in the initial stage. In recent years, the gas content measurement technology of underground long borehole high-pressure water sealed coring has been applied in the medium hard coal seam mining area with remarkable effects, but its application is limited in broken-soft coal seam. A number of issues are encountered that easy breakup of coal core sample, easy wall collapse of the bore hole, gas inrush from borehole, low success rate for coal sample coring, and large risk, when the existing coring technology through directional drilling and sealed high-pressure water is employed in the broken-soft coal seam. In order to solve the aforementioned issues and meet the demand of coal samples containing original moisture, a long-distance fixed-point closed coring technology process was proposed to use "gas coring drilling + gas conveying plugging ball + high-pressure water and gas combined sealing coal core" in the soft coal seam with double circulation medium. A long-distance dry closed coring system is proposed through downhole pressurized air sampling drilling, in which pressurized air is used instead of pressurized water for drilling slag discharge, core bit cooling and plugging ball transportation; air and water are combined to press. The sealed coring device in the hole is closed through the drive from a combination of wind and water. The main coal seam in the same area of a mine in Huainan mining area is selected for testing. The gas content of long-distance fixed-point closed coring in broken-soft coal seam is measured as 6.65~7.82 m³/t, while the gas content of conventional coring is measured as 5.11~6.45 m³/t. It is found that the gas content of airtight coring samples is generally higher than that of conventional coring samples. The research shows that the long-distance fixed-point closed coring technology in the broken-soft coal seam provides a new way to accurately measure the gas content in the broken-soft coal seam over a long-distance, thereby meeting the information demand for the gas occurrence information in the broken-soft coal seam in large areas and ensuring safe and efficient production in mines.