Study On High-Level Directional Drilling Drainage Technology In High Strength Production Face Of Low Gassy Seam

In recent years,with the continuous improvement of the level and capacity of coal mine production mechanization,a large number of oversize mines with production capacity exceeding 6.0Mt/a have emerged.There are a kind of special mines in these mines.The gas content of coal seam in these mines is not high,but under the condition of high-intensity mining,the absolute gas emission of working face reaches the standard of high gas mine,and the gas concentration in upper corner is too high or even beyond the limit.In view of this kind of mine,in recent years,the method of extracting pressure-relief gas from goaf by high-level directional drilling in roof has been adopted to control the problem of upper corner gas.For this method,it has certain theoretical significance and practical value to study how to arrange high-level directional drilling to extract pressure-relief gas from goaf and ensure safe and efficient production.This paper takes Wangjialing Coal Mine No.12318 working face of Shanxi Zhongmei Huajin Energy Company as the research object,which is a typical oversize coal mine with low gas content and high production intensity.Through the analysis of the present situation of high-level directional drilling extraction in the test face,the existing problems and corresponding solutions are obtained.Based on the research and determination of the "three zones" height range of caving caused by the backward spanning of overlying strata in goaf by the method of empirical formula calculation and numerical simulation,the correlation between the extraction effect of high-level directional drilling and its layout parameters is analyzed by adjusting the layout parameters of high-level directional drilling and field tests,and the proper layout parameter range of high-level directional drilling is determined.And the engineering application is also carried out to prove its rationality and analyze its gas prevention effect.The main contents of this paper are as follows:(1)Through the analysis of the present situation of gas extraction in the test face,it is concluded that there are some problems in the current high-level directional drilling extraction,such as the uncertainty of proper borehole layout parameters and the low concentration of gas extraction.(2)By using the method of combining empirical calculation formula with computer numerical simulation,the height range of caving "three zones" formed after overburden damage in goaf is obtained as follows: the maximum height of caving zone is up to 25 m,the maximum height of fracture zone is about 125 m,and the bending subsidence zone is above 125 m.(3)According to the height range of caving "three zones",through adjusting the layout parameters of high-level directional drilling and field tests,the correlation between the layout parameters of boreholes and their extraction effect is analyzed.Finally,the proper layout of vertical layer of high-level directional drilling in Wangjialing Coal Mine is determined to be between 25-49 m,proper layout horizontal distance range is between 30-60 m,and the overlap length between adjacent drilling sites is about 80 m.(4)The proper layout parameters of high-level directional drilling are applied in the field,and the rationality of the layout parameters is proved by comparing the extraction effect and gas prevention effect with that of previous drilling sites.