Research on Enhancing Gas Extraction Efficiency through CO₂ Gas Fracturing in Outburst-Prone Coal Seams

Given the background of significant Coal Mine gas disasters worldwide, the research and development of efficient gas control technologies have become critical to ensuring mining safety. CO₂ gas fracturing (CO₂-Frac), an innovative technology for Coal Mine gas control, has demonstrated efficiency in various mining areas across China. However, its application in outburst-prone coal seams is not yet fully understood. This study presents a field-scale CO₂-Frac project conducted in an outburst Coal Mine in China, specifically the Pingshu Coal Mine, where the previously employed dense-borehole gas extraction technology failed to efficiently achieve gas extraction and outburst prevention. The CO₂-Frac plan was evaluated through fracture propagation experiments utilizing both single-hole and dual-hole configurations, highlighting the advantages of the dual-hole CO₂-Frac method. Subsequently, on-site gas extraction tests were conducted to further assess the efficacy of the CO₂-Frac plan. The results indicate that (1) In the dual-hole CO₂-Frac scheme, the fractured and pressure relief area expanded to approximately 26.82 m², which is 220% larger than that of the single-hole scheme. (2) The dual-hole CO₂-Frac significantly enhanced gas extraction effectiveness, increasing the flow rate from 0.026 to 0.216 m³/min in a 100m borehole, a 7.3-fold improvement. Additionally, the gas extraction period to reach the standard was reduced from 20 to 6 days. These findings conclusively demonstrate that the dual-hole CO₂-Frac technique is an effective method for safe excavation in outburst-prone coal seams, providing both theoretical and practical validation for its application in similar geological settings.