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

Abstract

A proper understanding of liquid CO2 phase transition fracturing is essential, because the technique can not only reduce CO2 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 CO2 phase transition in the driving face of an outburst-prone coal seam. At first, the research theoretically analyzed the fracturing processing through the liquid CO2 phase transition and established a mathematical model for the fracturing pressure of the coal seam and the influence range of fracturing. Then, the CO2 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 CO2 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.