Permeability characteristics of deep coal seam and pressure relief technologies of the key first mined coal seam

In view of the complicated geological conditions of coal mining in China, the extensive development of coal seams in coal-bearing strata and the serious occurrence of gas disaster in outburst coal seam group, this paper analyzes permeability character of deep coal reservoir by combining theoretical analysis, data statisti cs with engineering practice and it shows that deep coal is natural pulverized and developed in micro, small pore with permeability usually less than 10-6μm2 .It propose s the connotation of the key first mined seam selection which is security, economy and master plane as well as the theoretical model of"drilling and unloading"for the ke y first mined seam.This paper ascertains the quantifying key indicators for ton coal drilling distance and bore space when burial depth is more than 800 m.On this basis, it is introduced that the technology approach for surface remaking by using hydraulic fracturing well and underground remaking by using bedding and piercing boreholes in China, which could cooperate with the pressure-relief gas extraction methods for the adjacent coal seams and form a three-dimensional gas extraction technology sy stem, realizing a safe and high efficient development of coal and gas resources in high gassy outburst coal mines.