Study on the proper position of gas drainage boreholes of L type based on the overlying fracture distribution in three dimensions induced by mining

Abstract：Gas drainage boreholes of L-type drilling from ground can save lots of roadway engineering and time compared with gas drainage roadway above the coal seam.In order to study the proper location of L-type boreholes, longwall panal 3213 in Xinjing coal mine was used as the in-site case.The overburden strata movement and fractures distribution in three dimensions induced by mining were obtained by discrete element software CDEM and physical similarity simulation test.The three-dimensional model of fracture field on the top of goaf was imported into software COMSOL.The gas migration law and gathering area around the goaf and its above area were obtained with different locations of L type drainage boreholes.The results showed that the gas concentration in the goaf could be effectively reduced by L type drainage boreholes.The proper position of the horizontal range of L type borehole was located on the middle-top range of fractured zone above the goaf.For longwall panal 3213, the proper position was 20～30 m above the coal seam in vertical direction and 15～30 m alternate of the tailgate in horizontal direction.The in-site drainage tests showed that the gas density was 78.5%, gas quantity was 8.58 m³/min that was 119 53 m³for a day extracted by the L type boreholes.The drainage gas was 42.60% of the total gas emission quantity in longwall panel 3213, which was very significant for the gas control in this coal face.

Keyword：mining-induced fractures in overlying strata;distribution in three dimension;L-type borehole;gas migration;numerical simulation;