Coal Geology & Exploration


The technological concept of sand fracturing at the high pressure side is proposed against the present situation where the coal mine downhole operation space is small, the power and water supply capacities are limited, and the surface sand fracturing equipment cannot be applied directly in the coal mine downhole. On the basis of the principle of sand mixing and carrying through hydrodynamic impact, the continuous hydraulic sand fracturing equipment at the high pressure side was developed. Such equipment requires no external power source for sand mixing. It forms cyclone impact through the changes in the flow regime and flow field of the fracturing fluid to realize sand mixing and carrying. As indicated by the theoretical analysis, numerical simulation and indoor simulation test, this equipment is feasible in principles, and can effectively mix and carry sand. The developed equipment has the overall pressure resistance of 55 MPa, 750 kg quartz sand can be loaded at one time, and can realize the continuous sand fracturing for a single crossing borehole or multiple crossing boreholes. The associated 3-channel shunt continuous hydraulic sand fracturing control system at the high pressure side of the coal mine downhole was designed. This system uses the mine compressed air to realize the on/off action of the switch, and coordinates with the fracturing pump control system to realize the remote concentrated control over the sand adding process, so as to ensure the safety and reliability during sand adding. The equipment was applied to carry out the field test for 5 floor crossing boreholes at the Pansan Coal Mine in Huainan Mining Area, Anhui. As indicated by the results, this equipment has high sand carrying capacity, and effective sand adding can be realized by only opening Channel II, with the maximum continuous sand adding amount of 150 kg and the maximum injected water amount of 316 m3. The gas extraction scalar quantity of the sand fracturing borehole and the gas extraction quantity of the 100 m borehole were 2.38 and 2.03 times of that of the water fracturing borehole, respectively, showing significant effects in permeability enhancement. The developed equipment can be applied in the fields, such as the coal mine downhole highpressure water jetting, hydraulic cutting and hydraulic sand fracturing.


high pressure side, hydraulic sand fracturing, gas extraction, Pansan Coal Mine in Huainan, underground coal mine




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