Research On The Effect Of Increasing Gas Extraction By Directional Long-hole Hydraulic Fracturing In Coal Seam

In order to solve the problem of gas extraction in high gas and low permeability coal seam of Longfeng Coal mine,such as low permeability coal seam,small amount of gas extraction and low extraction rate,9 # coal seam in Long Feng coal mine as the research object,by combining theoretical analysis,numerical simulation and the underground test,the anti-reflection technology of hydraulic fracturing is studied systematically,and field tests and applications are carried out.The main technical ideas include:Analysis the anti-reflection mechanism of hydraulic fracturing,and the multi-scale flow mathematical model of coal gas was constructed to simulate the influence range of anti-reflection of hydraulic fracturing.After the research and construction of directional long-distance down-hole drilling technology,the anti-reflection engineering practice of directional long-distance drilling hydraulic fracturing is completed.Finally,the anti-reflection effect of hydraulic fracturing is investigated by using the change of gas parameters in boreholes before and after fracturing and the electric method detection technology,combined with the extraction evaluation unit of optical force technology.The main research results of this paper are as follows:(1)Analyses the hydraulic fracturing antireflection crack extension process and the influence factors of the coal gas multi-scale flow mathematical model for hydraulic fracturing antireflection influence scope of numerical simulation.The results showed that the gas pressure in fracture decreased with the decrease of the distance from drilling hole.With the progress of gas extraction,the permeability and its influence range gradually increase,the increase range slowly decreases and tends to a constant value,but the maximum permeability is always located around the borehole.After 40 days of extraction,the influence radius of extraction is more than 3m.(2)Combined with the bottom suction of 5922 air tunnel and the actual geological situation,three directional long-distance downward holes with hole depth of 300 m and related construction technology are designed.After solving the problems existing in the construction technology,the construction of three directional long-distance downward hole drilling technology is completed.The actual drilling trajectory is basically consistent with the design trajectory,the drilling molding is good,and meets the expected requirements,providing a basis for directional long drilling hydraulic fracturing.(3)Complete hydraulic fracturing of three boreholes using different fracturing methods.One month later,the gas extraction concentration of the three boreholes is above 90%.The gas extraction concentration of the 9-6 boreholes is 60% higher than before fracturing and 90% higher than at the end of fracturing.When the negative pressure is 20 k Pa,the extraction flow is about 20 times higher than that at 15 k Pa.The net flow rate of 9-5 drilling hole increased by about 100 m3 at the maximum net flow rate,which was about 4 times of that before fracturing,effectively improving the gas extraction efficiency.According to the analysis of the microseismic monitoring system,the fracturing was mainly concentrated on both sides of the 9-4 holes,affecting a range of about 30 m,and increasing resistance between 100 and 400 Ω·m.According to GLTech extraction evaluation,the daily extraction net flow rate has increased five times to about 0.35m3/min,and the daily extraction net flow rate has reached 500 m3.The expected extraction standard will be reached by the end of 2021.