Abstract: In order to solve the problem of low gas drainage concentration and ensure extraction safety in coal seams, the reason for gas leakage in the plugging section and the mechanism of pressure loss in effective gas extraction section were analyzed. The analysis showed that the amount of air leakage is inversely proportional to the grouting pressure and the plugging length, and is proportional to the pore size and negative pressure of gas extraction, and the whole screen mesh tube technology for the effective gas extraction section can reduce the negative pressure loss along the path. Based on this, the "two plugging, one injection and one discharge of full net pipe" integrated device was designed. The engineering practice shows that compared with the "two plugging and one injection" sealing method, under the same conditions, the gas volume by "two plugging, one injection and one discharge of full net pipe" sealing method increases by 54.33%, and that the average gas concentration by "two plugging, one injection and one discharge of full net pipe" method is 125.82% higher than that by "two plugs, one injection, one row of full net straight pipe" after hole collapse.

Key words: two plugging, one injection and one discharge of full net pipe, mechanism analysis, gas leakage in plugging section, pressure loss along path, gas extraction efficiency