Attenuation Evolution Characteristics Of Gas Drainage Flow Rate Of Drainage Borehole In High Gas Coal Seam

Gas drainage is a fundamental technical measure to achieve gas disaster prevention and control.However,due to the differences of coal seam physical properties,gas occurrence and extraction parameters,the gas drainage effect will also show great differences.Studying the key influencing factors of coal seam drainage and its flow attenuation characteristics has important guiding significance for coal mine gas drainage design.In this paper,the key influencing factors of the cross-measure borehole and bedding borehole are studied,and the attenuation characteristics of the gas drainage flow are verified by field measurements.The main research progress is as follows:(1)The microscopic pore structure of coal was tested and studied.It is found that the coal sample of Pingdingshan No.12 coal mine has a rough surface structure,and the surface area in contact with the outside is large,which is more conducive to the adsorption of gas,and the pores are developed in a large amount,which is more conducive to the storage of gas.However,the fracture of the coal body is poorly developed,resulting in poor connectivity in the coal seam,which is not conducive to gas migration.(2)The influencing factors of gas drainage in single-hole drilling were studied.It was found that the growth radius of gas drainage in the initial period was larger than that in the latter period.With the increase of drilling diameter,the effective radius of drilling also increases,but this effect is not obvious,at the same time,the negative pressure of drilling has a small effect on the radius of drilling.At the same time,the impact of the suction negative pressure on the borehole extraction radius is small.In addition,the single-hole extraction gas flow rate of different inclination drilling holes is simulated,but when the angle between the drilling hole and the coal seam is small,the influence radius of gas drainage is large,and the gas drainage flow rate is also large.(3)Numerical simulation was carried out on the drainage means under the coupling condition of multi-boreholes along the bedding,and it was found that five different drilling intervals(1 m,2 m,3 m,4 m,and 5 m)had a great influence on the drainage effect.After the drilling was arranged at an interval of 1 m to 5 m,the diameter of the outburst elimination in zone was enlarged by 1.25 times.With the increase of borehole diameter,the diameter of the outburst elimination in zone under the coupling action of 5 bedding boreholes increases gradually.In addition,it can be seen that along with the extension of drainage time,the outburst elimination in zone of coupling borehole in bedding and porosity increases gradually.In the same time interval,the growth range of the outburst elimination in zone in the initial stage is greater than that in the later stage.It is also found that the negative pressure is not the main factor and determinant of the drilling radius.(4)Field tests were carried out to track the drainage flow and concentration of the borehole.It was found that the flow and concentration of the borehole showed three trends:(1)The drainage flow and concentration showed exponential decaying trend,and the power exponent of the exponential function was negative;(2)Although the drainage flow and concentration also show an exponential attenuation trend,the attenuation rate is very different,and The power exponent of the exponential function was positive;(3)The drainage flow and concentration increased first(the connected drainage lasted for about 22 ~ 25 days),and then showed an exponential decay trend.This paper has 31 figures,12 tables and 53 references.