Study On Gas Extraction Technology Of High Directional Long Borehole In Complex Rock Strata

With the raising of coal mining intensity and mining depth,the amount of gas emission is also raising,part of which comes from the goaf.Therefore,for the sake of ensure the security of coal mine production,it is essential to treat the goaf gas as the key work.This paper takes 172107 working face of complex rock strata in Dashucun Mine as the research object,analyze the geological law of mine gas,study the evolution law of mined-out fracture field,and use COMSOL numerical simulation software to study the gas migration and distribution law of goaf.Finally,the gas extraction technology research was carried out on the 172107 working face,and the extraction effect of high directional long borehole and ordinary high borehole was compared and analyzed.The main achievements are as follows:(1)The burial depth is the most important factor affecting the gas content in 2#coal seam of Dashucun Mine,which conforms to the following statistical law:y=0.0473x-12.4(2)Through theoretical calculation and numerical simulation,the height of three belts in the goaf of 172107 working face was investigated,and the height of caving belt was determined to be 12 m,and the height of fracture belt was determined to be 12 m～46 m.According to the theoretical calculation and numerical simulation results,it is concluded that the overlying rock fissure morphology can be replaced by a space structure similar to trapezoidal skeleton,and the main parameters of overlying rock caving morphology are determined.(3)Using the method of separate source prediction,it is calculated that the gas emission from goaf accounts for 31% of the total gas emission,and the gas emission from falling coal and coal wall accounts for 69% of the total gas emission.Using COMSOL numerical simulation software,the gas migration and distribution law in goaf under U-shaped ventilation condition of complex rock face is simulated numerically.It is concluded that the gas migration and distribution rule in goaf is as follows: the gas concentration along the dip changes from no obvious change in the intake roadway to a sudden increase in the return air roadway;the gas concentration along the advancing direction of working face increases with the goaf depth increasing,and the gas concentration increases gradually in the vertical direction.(4)The high directional long borehole with a maximum hole depth of 538 m was constructed in the working face of complex strata.The drainage practice shows that the high directional long borehole covers a wider area than the ordinary high borehole,and the extraction effect is stable,so it can replace the ordinary high borehole for gas extraction in goaf.This paper has 29 figures,8 tables and 70 references.