Elimination of coal and gas outburst risk of an outburst-prone coal seam using controllable liquid CO2 phase transition fracturing.

• Mathematical model for the effective fracture radius was established. • The fracture zone around the blasting hole is distributed approximately in an ellipsoid. • Field test indicated that the gas drainage effect significantly improves. A proper understanding of liquid CO 2 phase transition fracturing is essential, because the technique can not only reduce CO 2 emission, but also can increase production of coalbed methane (CBM). In order to improve the speed of gas drainage and increase the gas permeability of a low permeability coal seam in the driving face of an outburst-prone coal seam, this paper introduced the technology of pressure relief and antireflection by liquid CO 2 phase transition in the driving face of an outburst-prone coal seam. At first, the research theoretically analyzed the fracturing processing through the liquid CO 2 phase transition and established a mathematical model for the fracturing pressure of the coal seam and the influence range of fracturing. Then, the CO 2 phase transition fracturing was numerically simulated. Numerical simulation results showed that the influence radius of fracturing was 2.55–2.70 m. Finally, the field test on liquid CO 2 phase transition fracturing was conducted in the driving face based on the modeling results. The results of field experiments show that the amount of head-on gas emission increased by about 2 times after blasting, and the quantity of gas extraction from a single borehole controlled by fracturing was increased by about 4 times. After 8 h of blasting, the amount of gas emission and drainage decreased to the level before blasting. The outburst suppression effect is obvious after a comparison of the gas desorption index of drilling cuttings within 20 m before and after blasting in the heading face. [ABSTRACT FROM AUTHOR]