An advanced CO₂ gas-phase fracturing technology for efficient methane drainage, outburst prevention and excavation in outburst coal seam

Coal and gas outburst in coal mines is a serious disaster in China. Although the disaster has been reduced significantly over the past 10 years, vicious accidents still occure, causing serious losses to the lives of miners and the safety of coal mines. The current applied technologies for outburst prevention and control include hydraulic fracturing, hydraulic slitting, hydraulic flushing, deep hole blasting, intensive drilling, etc., which have solved the outburst problem and safe excavation in some degrees. Nevertheless, the above-mentioned technologies could not solve the problems of safety excavation in the high gas content and low permeability outburst coal seams. Therefore, preventing outburst technology is still a major difficulity in China's coal mines. The carbon dioxide gas fracturing and outburst elimination technology has been developed in Xinyuan Coal Mine of Shouyang County in Shanxi recently and has achieved good results. This paper introduces its technical characteristics, field test method and the effect of anti-burst excavation based on working face 31002 of Xinyuan Coal Mine. The No.3 coal seam of Shanxi Formation mined in Xinyuan Coal Mine is a low-permeability and outburst seam. In the early stage, intensive borehole drilling and gas pre-drainage were used to prevent gas outburst, which took a long time to reach the gas drainage standard, with a low excavation speed. Efficient gas extraction, prevention of coal and gas outbursts, and ensuring the safe and rapid excavation of coal roads are major technical problems for the safe and efficient production of Xinyuan Coal Mine. The key points of the CO₂ gas fracturing technology are described as follows. Implementing 2 holes for CO₂ gas-phase fracturing in front of the tunnel face and drilling additional 9 holes for gas drainage covering a safety range of 15 m in each side of the roadway. All the 11 boreholes were connected to the drainage network for 3-5 days, and the excavation resumed after the outburst prevention parameter K₁ value reached the standard. The test data show that show that the CO₂ gas fracturing significantly enhanced gas drainage efficiency and the coal cannon and other dynamic phenomena are reduced. With K₁value reduced, the gas concentration in the roadway can be reduced and homogenized during coal cutting, ensuring a continuous safe driving. It is concluded that CO₂ gas-phase fracturing can achieve high-efficiency gas extraction and prevention of outbursts, and it can be applied in coal mines with similar gas geological conditions across the country.