Research and application of CO2 gas fracturing for gas control in low permeability coal seams

With the progressive increase of the mining depth,gas related mine hazards are getting worse since gas con-tent and gas pressure naturally elevates. In the study,a novel methane control technology namely CO2 gas fracturing (CO2 -Frac),has been proposed and investigated in Luan coal mine field. The CO2 -Frac is achieved by directional multiple stage CO2 gas fracturing with a newly renovated CARDOX system. The key mechanism of CO2 -Frac is to re-duce local stress and gas pressure,and increase permeability effectively. Mine-scale tests on CO2 -Frac have been con-ducted in five coal mines in Luan mine field from 2011 to 2015. It was observed that gas outburst tendency was re-duced,permeability and methane drainage effectiveness (concentration and flow rate) in the CO2 -Frac boreholes were significantly improved,and drainage time was shortened to 210 days from 720 days. The CO2 -Frac is confirmed as the best technology to control coalmine gas disaster in this low permeability coal seams in Luan mine field,and it can be effectively applied in the gassy coalmines with similar geology conditions cross the county. This paper delineates the key research findings of this five year project including the CO2 Frac procedure,the fracture initiation and prorogation mechanism,methane drainage results,and how to optimize fracturing direction.