Structural control on pore-fracture characteristics of coals from Xinjing coal mine, northeastern Qinshui basin, China

Deformation characteristics and pore structure of coals from Xinjing coal mine have been studied, as well as the control mechanism of structural deformation on coal structure characteristics, based on observation in coal mine and deformation analysis of typical coal samples, combined with microscopic observation and mercury intrusion porosimetry (MIP). The research has revealed that coals of Xinjing coal mine mainly suffered from brittle deformation and consisted of primary and cataclastic structural coal, and a small part of intensively deformed coals develop locally in no. 3 coal seam. With the structural deformation enhanced, the coal strength becomes worse, the mortar textures and fracture density increase, and the scale and aperture of fractures increase at first and then decrease. The pores of coal, with high total pore volumes and porosity, are mainly composed of micropores and transitional pores, and the pore volumes of macro-and mesopores vary over a large range. The number of macropores greatly correlates with the density and aperture of joints and fractures, and the number of mesopores is determined by the enrichment of mortar textures. Three pore structures are proposed according to the shapes of intrusive mercury curves, of which the parallel type has good pore connectivity and improved permeability, the angular type has both good pore connectivity and permeability induced by the structural modification, and the double S type has poor porous connectivity which is unfavorable for coalbed methane exploitation and most possible for coal and gas outburst during mining.