Design And Application Of High Level Drilling Borehole Based On Overburden Crack Evolution Law

With the deepening of the coal mining gradient,a large number of shallow mines have gradually transformed into deep mines,which makes the occurrence of gas more and more complicated,and the problems caused by the complexity of the occurrence of gas are becoming increasingly serious.Therefore,under complex gas conditions,reasonable selection of optimal high-level drilling parameters to achieve the effect of low cost and high recovery rate is of great significance for reducing gas hazards in coal mining and improving gas recovery utilization.Based on the gas geological data and the actual situation in the field,the evolution law of overburden rock fissures and the characteristics of gas flow in goaf of 150112 working face in the edge coal industry are analyzed and studied by means of comprehensive research methods such as theoretical analysis,field monitoring and numerical simulation.It is found that the caving zone and fissure zone are analyzed when the overburden rock is destroyed by using 3DEC numerical simulation software.Evolution law and height distribution range of the two zones are basically consistent with theoretical calculation results,so it is judged that the maximum height of the caving zone is 8-13 m and the maximum height of the fracture zone is 58.4-65.5m.Before the high-level borehole extraction is not used,the gas concentration in the goaf is larger,the distribution range is larger,the closer to the goaf,the higher the gas concentration in the deep part of the goaf,and the gas concentration in the upper corner of the working face.The gas concentration in the whole goaf decreases gradually after high-level borehole extraction,and the gas concentration in the upper corner of the goaf also meets the requirements of safe production.Based on the above research results on the evolution law of overburden fissures and gas flow characteristics in goaf,the design scheme of high-level boreholes in overburden strata of 150112 working face is determined.When high-level boreholes are used to extract gas,the overall extraction concentration is higher,and the gas concentration of high-level boreholes can reach more than 90%,while the gas extraction quantity of high-level boreholes gradually increases with time,and the overall change trend is obvious.In the whole process of gas extraction,because the high-level boreholes may be in caving zone or borehole collapse,the gas extraction concentration is on the low side,and the fluctuation of gas extraction concentration is periodic fluctuation law affected by mining,that is,"initial mining period-growth period-attenuation period".Therefore,through comprehensive analysis of the high-level boreholes,the gas extraction concentration and extraction volume change.The regularity of chemical characteristics further verifies the rationality of the design scheme of drilling parameters in the overburden strata.There are 27 figures,16 tables and 63 references in this paper.