Study On The Influence Mechanism Of Gas Drainage Concentration In Bedding Boreholes And Its Control Optimization

The extraction of gas from coal bodies through construction boreholes has the advantages of high safety and low economic cost.It is one of the most important methods in the current coal mine gas control work in my country.However,in the actual coal mine gas drainage process,as the drainage work progresses,the gas in the coal body is gradually extracted,and the gas concentration of the gas extracted in the borehole decreases,which not only increases the risk of gas explosion in the pipeline,but also is not conducive to Extract gas for reuse.Therefore,on the basis of related theories such as fluid mechanics,seepage mechanics,rock mechanics,etc.,this paper adopts theoretical derivation,assignment analysis,physical similarity simulation,numerical simulation,and field measurement research methods to determine the gas flow rate and air leakage in the borehole The basic idea of gas drainage concentration in the borehole has been systematically studied on the factors affecting the gas drainage concentration and its changing law,and finally the following conclusions are drawn:(1)Combining the law of gas occurrence and flow in the coal body,use Darcy's law to derive the gas flow calculation formula in the borehole,and on the basis of analyzing the characteristics of the coal body stress changes around the borehole,combined with the seepage mechanics equation to derive The formula for calculating the amount of air leakage in the borehole is presented.The gas flow acceleration is used to characterize the instantaneous change trend of gas flow and gas leakage in the borehole,and the gas drainage negative pressure control limit is determined by the acceleration ratio W of the two.(2)Designed and established a physical similarity simulation experiment for the influence factors of negative pressure on gas drainage concentration.By changing the parameters of gas pressure is low,the drainage concentration It shows a trend of first increasing and then decreasing.Afterwards,through the experiment of the factors affecting the leakage of air by the negative pressure of extraction,it was found that the small coal powder around the borehole will be affected by the negative pressure of the extraction and move along the fissures and adsorb and block the air leakage channel.Based on this,it is proposed to install the extraction in stages.The idea of using negative pressure to increase the concentration of gas drainage.(3)Using COMSOL numerical simulation software,combined with the actual parameters of coal at ZF215 working face of Jiangjiahe Coal Mine,simulated the scalar amount of gas drainage,air leakage,and drainage in boreholes under different coal permeability and drainage negative pressure conditions.The change and law of concentration.It is concluded that the increase in suction negative pressure has a more significant impact on the amount of air leaking into the borehole.Therefore,when the absolute sealing of the borehole cannot be guaranteed,when the concentration of gas drainage is attenuated,it can be adopted Appropriately reduce the negative pressure of drainage to achieve the purpose of increasing the concentration of gas drainage.(4)On-site determination of the best drainage negative pressure is carried out at the ZF215 working face of Jiangjiahe Coal Mine.The drainage negative pressure is set by gradient arithmetic change,and the gas concentration explosion limit is 16%as the boundary.When the gas drainage concentration drops to 16%The secondary plugging method of injecting plugging powder is used to improve the gas drainage effect.The best drainage negative pressure is 30kPa before the gas drainage concentration is attenuated to 16%,and the best drainage is determined after the second plugging.The negative pressure for mining is 45kPa.This method can make the gas drainage concentration above 16%for 78 days,ensuring the smooth completion of the gas control work at the working face.