CLADDING TECHNOLOGY SHANXI CO., LTDExperimental Study of CO2 Fracturing Device in Aneng Coal Mine
Field Trial Overview and Objectives
The Aneng Coal Mine, located in the Yanzhou Coal Mining Group in Shandong Province, China, has been selected as a field trial site for the CO2 phase-change fracturing technology. The mine operates in a thick, gassy coal seam with a thickness of 4.5 to 6.0 meters, a gas pressure of 2.0 to 3.0 MPa, and a gas content of 8 to 12 cubic meters per ton. The coal permeability is extremely low, typically below 0.05 millidarcy, making conventional gas drainage methods ineffective. The field trial aims to evaluate the effectiveness of the CO2 phase-change fracturing technology in enhancing the gas drainage efficiency and reducing the gas pressure in the coal seam. The trial also aims to assess the safety, reliability, and economic viability of the technology for industrial-scale application.
Trial Design and Implementation
The field trial was designed with a control group and a treatment group. The control group consisted of conventional gas drainage boreholes without fracturing, while the treatment group consisted of boreholes with CO2 phase-change fracturing. The boreholes were drilled at a spacing of 4 meters, with a depth of 150 meters and an inclination angle of 5 degrees. The CO2 fracturing device was positioned at a depth of 80 to 120 meters in the treatment boreholes, and the charge pressure was set at 12 MPa. The boreholes were sealed with a cement-clay composite plug, and the initiation was triggered remotely with a delay of 30 seconds. The gas drainage performance was monitored for 4 weeks after the fracturing operation.
| Trial Parameter | Control Group | Treatment Group |
|---|---|---|
| Borehole spacing | 4 m | 4 m |
| Borehole depth | 150 m | 150 m |
| CO2 charge pressure | N/A | 12 MPa |
| Fracturing device depth | N/A | 80-120 m |
| Monitoring period | 4 weeks | 4 weeks |
| Number of boreholes | 10 | 10 |
Results and Performance Evaluation
The field trial results demonstrated a significant improvement in gas drainage efficiency in the treatment group compared to the control group. The gas drainage volume in the treatment group was 45 to 65 percent higher than in the control group during the first week after fracturing. The gas concentration in the treatment group was also higher, indicating that the fracturing had created effective flow pathways for the gas. The pressure decline rate in the treatment group was also faster, indicating that the fracture network had enhanced the gas drainage efficiency. However, the enhancement effect gradually declined over time, with the gas drainage volume in the treatment group approaching that of the control group after 4 weeks. This decline is attributed to the gradual sealing of the fractures by coal fines and water.
Safety Assessment and Quality Control
The safety of the CO2 phase-change fracturing operation was assessed through a comprehensive review of the operational procedures, the quality control of the fracturing device, and the monitoring of the gas environment. The fracturing device was fabricated from high-strength steel with full-penetration welds inspected by ultrasonic testing, and each device was hydrostatically tested at 1.5 times the maximum working pressure. The initiation system was designed with a safety delay of 30 seconds to ensure that all personnel had evacuated the area before the fracturing event. The gas concentration in the borehole and the surrounding area was monitored continuously, and no abnormal gas accumulation was observed during the trial. The quality control of the fracturing device was documented and traceable, with each device accompanied by a quality certificate including the material certificate, welding procedure qualification, and non-destructive examination report.
Study Insights and Industrial Application Prospects
The field trial at Aneng Coal Mine has demonstrated that the CO2 phase-change fracturing technology is technically viable and effective for enhancing gas drainage in high-gas low-permeability coal seams. The technology offers a significant improvement in gas drainage efficiency, with a 45 to 65 percent increase in gas drainage volume in the first week after fracturing. The safety of the operation has been confirmed through rigorous quality control of the fracturing device and careful operational procedures. The economic viability of the technology is also attractive, with the cost of the fracturing device and the operation being significantly lower than the cost of alternative gas drainage technologies. Future industrial-scale applications should focus on optimizing the fracturing parameters through numerical simulation and field validation, extending the effective drainage period through the use of proppants, and developing automated monitoring systems for real-time tracking of the gas drainage performance. The successful application of the technology at Aneng Coal Mine provides a valuable reference for the widespread adoption of CO2 phase-change fracturing in the Chinese coal mining industry.