CLADDING TECHNOLOGY SHANXI CO., LTDApplication of Carbon Dioxide Fracturing Technology in Coal Breakthrough Process at Jinjia Coal Mine 212 Transport Crosscut
Literature Overview and Technical Context
This study note addresses the application of carbon dioxide (CO2) fracturing technology during the coal breakthrough process in the 212 transport crosscut at Jinjia Coal Mine. The research focuses on using liquid CO2 phase-change fracturing to pre-fragment coal and rock masses, thereby reducing the risk of coal and gas outbursts, controlling dust generation, and improving the safety and efficiency of underground excavation operations. The technology is particularly relevant in deep coal mines where high gas pressure and brittle rock masses create significant hazards during the critical phase of breakthrough from roadway to coal seam.
The core principle behind liquid CO2 fracturing relies on the rapid phase transition of liquid CO2 from a high-pressure liquid state to a gaseous state when released into a confined borehole. This phase change produces a dramatic volume expansion — approximately 500 to 600 times under standard conditions — generating sufficient pressure to initiate and propagate fractures in the surrounding coal and rock mass. The technology offers advantages over conventional hydraulic fracturing, including lower water usage, faster operation cycles, and the ability to work in water-sensitive formations.
Core Technical Parameters and Process Description
The following table summarizes the key technical parameters associated with the CO2 fracturing system applied in this study:
| Parameter | Typical Value | Remarks |
|---|---|---|
| Liquid CO2 injection pressure | 15–20 MPa | Controlled by high-pressure pump system |
| Borehole diameter | 75–95 mm | Standard drilling equipment |
| Borehole depth | 3–6 m | Adjusted based on coal seam thickness |
| Number of boreholes per cycle | 4–8 | Arranged radially around crosscut |
| CO2 charge per borehole | 15–30 kg | Depends on rock strength and gas content |
| Phase-change expansion ratio | 500–600:1 | From liquid to gas at atmospheric pressure |
| Fracture initiation pressure | 80–150 MPa | Generated in confined borehole |
| Effective fracturing radius | 2–4 m | Measured by post-fracture permeability tests |
| Cycle time per operation | 2–4 hours | Including preparation and safety verification |
The process involves several critical steps: borehole drilling in the coal or rock mass ahead of the excavation face, installation of a liquid CO2 fracturing device with a sealed borehole plug, pressurized injection of liquid CO2 into the device, and controlled initiation of the phase-change reaction. The resulting fractures increase the permeability of the coal mass, allowing trapped gas to migrate and be extracted more effectively before the face advances.
Application Effectiveness and Engineering Outcomes
The application of CO2 fracturing technology in the 212 transport crosscut demonstrated measurable improvements across multiple performance indicators. The following table presents the comparative results:
| Performance Indicator | Before CO2 Fracturing | After CO2 Fracturing | Improvement |
|---|---|---|---|
| Gas emission concentration at face | 1.2–1.8% | 0.4–0.6% | 60–70% reduction |
| Dust concentration | 8–12 mg/m³ | 3–5 mg/m³ | 55–65% reduction |
| Excavation advance rate | 1.5–2.0 m/day | 2.5–3.5 m/day | 60–75% increase |
| Roof pressure events | Frequent | Rare | Significant decrease |
| Coal burst risk | Moderate-high | Low | Substantially mitigated |
| Borehole drilling resistance | High | Reduced | 30–40% less energy |
The technology also contributed to improved working conditions by reducing the frequency of roof pressure events and minimizing the need for repeated support reinforcement. Post-fracture permeability measurements confirmed that the effective fracturing radius reached approximately 2 to 4 meters, which is sufficient to influence the gas flow field in the immediate vicinity of the excavation face.
Key Technical Challenges and Countermeasures
Several challenges were identified during the implementation of this technology, and corresponding countermeasures were developed:
- Borehole sealing integrity: Maintaining a reliable seal in soft coal and fractured rock conditions is critical. The study employed a two-stage plug system with a steel sleeve outer plug and a polyurethane foam inner seal, achieving sealing pressures exceeding 25 MPa.
- Controlled initiation timing: Precise timing of the phase-change initiation is essential to avoid premature fracture or delayed detonation. A temperature-triggered initiation mechanism was used, calibrated to initiate within 30–60 seconds of reaching the target pressure.
- Fracture direction control: Achieving the desired fracture orientation toward the excavation face requires careful borehole arrangement and angle optimization. The study used a radial borehole pattern with 15–25 degree inclination angles to maximize fracture intersection at the face.
- Safety verification: Post-fracture gas monitoring and borehole pressure measurements were conducted before resuming excavation to ensure that residual gas pressure had been sufficiently reduced.
Study Insights and Engineering Implications
From a broader engineering perspective, the CO2 fracturing technology represents a significant advancement in the management of gas and rock burst hazards in underground coal mining. The technology aligns with the principles of proactive hazard mitigation rather than reactive support reinforcement. The phase-change energy mechanism provides a reliable and repeatable means of generating high pressures in confined spaces without the need for explosives or complex hydraulic systems.
One notable insight from this study is the importance of integrating fracturing with gas drainage systems. The fractures created by CO2 phase change serve as enhanced pathways for gas extraction, but the effectiveness depends on the subsequent drainage infrastructure being properly designed to capture the released gas. This integration is essential for achieving the full safety benefits of the technology.
Another important observation is the adaptability of the CO2 fracturing system to different geological conditions. The key parameters — borehole depth, CO2 charge, and borehole arrangement — can be adjusted based on coal seam thickness, gas content, and rock strength. This flexibility makes the technology suitable for a wide range of mining environments, particularly in deep mines where conventional methods may be insufficient.
The study also highlights the economic viability of the technology. While the initial equipment investment is moderate, the operational cost per cycle is relatively low due to the reusability of the fracturing devices and the low cost of liquid CO2 as a consumable. The economic benefits are realized through increased advance rates, reduced support costs, and fewer safety incidents, which collectively improve the overall productivity and safety record of the mine.
In conclusion, the application of CO2 fracturing technology in the 212 transport crosscut at Jinjia Coal Mine demonstrates a mature and effective approach to managing gas and rock hazards during coal breakthrough operations. The technology offers a practical solution to a persistent challenge in underground mining, and its continued development and standardization will likely lead to broader adoption across the industry.