Technology of gas extraction by deep hole directional drilling in underground coal mine and its applicatio

In order to solve problems of slow tunneling and tension of mine excavation replacement in test mine using traditional extraction technology, a scheme of using deep hole directional drilling with long directional drilling instead of conventional drilling to carry out coal seam gas extraction was proposed. Directional drilling has a large effective area on coal seam, which can change distribution of original coal stress in a large range, thus breaking dynamic balance of gas adsorption and desorption in coal seam and transforming a large number of adsorbed gas into free state; Under the action of pressure gradient formed by drilling negative pressure and coal ground stress and gas pressure, free gas flow continuously to drilling space, make the surrounding coal gas emission effectively, cause shrink deformation of coal, permeability coefficient increases significantly, ground stress and gas pressure gradient are reduced, so as to make the long drilling directional extraction influence range expanded, realize the effective gas extraction from coal seam in a large area. The test results show that using deep hole directional drilling with long directional drilling can get a well formed hole and has obvious effect in gas extraction. Total drilling footage of the test hole is 2 213 m,the maximum drilling depth reaches 523 m, and the average daily extraction pure quantity is 3 528 m3. The average volume fraction of gas extraction is up to 88.3%, and the highest value is 98.0%. The average single-hole gas extraction pure quantity is 1.23 m3/min, and the maximum value exceed 2 m3/min. Compared with conventional drilling extraction, the pure quantity of single-hole gas extraction of directional drilling is increased by more than 16 times, the volume fraction of single-hole gas extraction is increased by 2-4 times, and monthly average footage of roadway is increased by more than1 times.