Experimental study and application of directional subdivision hydraulicfracturing and permeability improvement device

Directional subdivision hydraulic fracturing is one of the most effective ways to increase permeability of coal seams. The basic principle of directional subdivision hydraulic fracturing technology is introduced in the paper. Laboratory tests were conducted to explore the characteristic of subdivision hydraulic fracturing key device. The results indicate that the high pressure sealing has good expansibility and anti-contractility and the end plugging torque of the water injector should be set at 3 N·m or more. The experiment results were then validated through practical applications in Pansidong coal mine. It show that the initiation pressure of 13-1 coal seam is 28～30 MPa,the time of single-stage fracturing 10 m is about one hour, and the water consumption is 10～13 t. It is also found that the fracturing time and water consumption of directional subdivision hydraulic fracturing are much less than those for full hole hydraulic fracturing technology.After directional hydraulic fracturing, the average gas concentration of coal seam is increased by 1.72～3.04 times, the average mixed flow rate is increased by 2.00～4.04 times, the average daily extraction capacity is increased by 2.94～10.87 times. This paper proves that the directional subdivision hydraulic fracturing device could effectively increase the permeability of coal seam.