Technology of Rapid Outburst Elimination by Liquid CO₂ Fracturing in Region of Coal Uncovering

Aiming at the characteristics of the larger outburst elimination amount, complex working link and the long cycle of uncovering coal in the process of crosscut coal uncovering in low permeability outburst seam, the technology of liquid CO₂ phase transition fracturing was used in gas drainage hole. The permeability increase radius of No.4 coal seam is 6 m by theoretical calculation and field investigation. The technology was tested in the face of -650 transport lane which would uncover the No.4 coal seam. The results showed that the average drainage concentration from a single gas borehole increased from 20.2% to 42.6%. The average single hole drainage quantity increased from 1.56 m³/d to 3.76 m³/d before and after fracturing. Gas drainage maintained efficient in the past 20 days. Drainage standards were completed in a month. The extraction rate was 48.16% and the extraction time was shortened by 43%. The average residual gas content was 5.41 m³/t, and the average residual gas pressure was 0.27 MPa. The maximum drilling cuttings volume S was 4.7 kg/m and desorption index of drill cuttings △h₂ was 140 Pa. All test values were less than the critical value. The return air gas concentration is only 4% after the uncovering coal seam, which achieved safe, efficient and rapid cross-cut coal uncovering.