Research On Permeability Improvement Technology Of Hydraulic Fracturing In Crossing Borehole Of Tectonic Coal In Yuxi

The Yuxi mining area is a high gas field, soft coal, small permeability coefficient, low gas extraction rate are its peculiarity,so the gas disaster such as coal and gas outburst is becoming a major threat to the mine safety and efficient production,and a certain amount of technology is urgently needed to better improve the permeability of coal seam. Hydraulic fracturing as permeability improvement technology has been widely used in recent years, as well as its better results.However, because of the difference of tectonic conditions in different mines, the fracturing process parameters are also different.Based on the gas geological conditions in the study area,the factors such as coal seam's characteristics, in-situ stress(size and direction), gas content and so on that influence hydraulic fracturing cracks distribution form and gas extraction rate are analyzed. Then according to the basic principle of hydraulic fracturing and theory of elastic mechanics, the hydraulic fracturing pump pressure(fracture pressure and frictional resistance) is calculatied; Based on the filtration effect of hydraulic fracturing shape prediction model, fracture geometry size is analyzed and calculatied after hydraulic fracturing; Using the method of mathematical statistics, the permeability, the concentration of gas extraction, the extraction flow, the radius of influence,the damping period are contrast before and after hydraulic fracturing; The following results are obtained:The fracture pressure is about 13 MPa ~ 15 MPa in the depth of 500 m,and the maximum pump pressure is between 20 MPa ~ 25 MPa; Water fracturing fluid has a certain effect in the research area;The produced crack is vertical,and the crack's length is between 50 m and 60,the wideth is 0.0015m~0.002 m,the height is about 10m; The effect radius of fracturing is about 60 m,and after fracturing, the gas extraction concentration is increased by 50% ~ 200% as well as the extraction flow rate increased by 60% ~ 300%; Based on the mathematical method of AHP,it is concluded that comprehensive effect of hydraulic fracturing about outburst prevention is better than hydraulic flunshing.Therefore, the hydraulic fracturing has good pressure relief anti-reflection effect in Daping mine, and can be good popularization and application value in Yuxi coalfield. It can be widely applied in the similar mine gas geological conditions.