| In some way,the relationship between coal mining and gas extraction is mutual restriction.When working face gas emission exceeds ultimate value,coal mining face advancing rate would be reduced.Gas control is an essential link in coal mining.For regional coal seam gas extraction,Kilometer and directional drilling has a huge superiority.It can effectively drain coal seam gas which has a complex occurrence condition.In order to determining km drill rational arrangement horizon in lower slice during the special thick coal seam slice mining process and improving the effect of km drill gas extraction,the paper took Tingnan 205 working face stratified gas extraction as an example,and studied how to use km drill draining lower slice gas under the influence of coal mining.This paper measured 205 working face gas basic parameters,and calculated working face gas extraction,and analyzed working face gas sources during the special thick coal seam slice mining process and key contents of gas control in the field.Through coal and rock stress permeability experiment,the paper got the relationship between vertical stress and permeability.Combined with mechanics model,the distribution of lower slice stress field and permeability were calculated.The calculation results showed that lower slice coal stress completely released under the influence of coal mining.And coal seam permeability was better within 5 meters.Based on numerical simulation,the paper studied the distribution of drill plastic zone during loading and unloading process in different conditions.And according to drill drainage failure criteria,drill failure horizon was calculated.As a result,stress and damage have a good correlation,and damage risk exists within 5.2 meters.Finally,on-site industrial test was carried out in Tingnan 205 working face.Through analyzing km drill gas drainage parameters in the different arrangement horizon,the results show that optimal gas extraction horizon is 5 m?7 m. |
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