Microstructure of mid and high rank coals from Qinshui basin, North China and its contribution to coalbed meathane

To better understand the relationship between micro-structures and coalbed methane(CBM), characterisation methods including microscopic 'photometer, scanning electron microscopy (SEM), mercury porosimetry, nitrogen adsorption at 77K and methane isothermal adsorption were introduced into investigating the adsorption capability of coal reservoir. The results reveal that the micropores volume has a increasing trend with increased vitrinite reflectance. The most favorable pore type is to have good connectivity, very good micro-pores porosity and good adsorption capability. Statistical analysis shows that endo-microfractures are the main type microfractures of Qinshui basin. Based on the results of coal macerals, coal lithotypes, it is found that the bright coal and telocollinites are favorable for endo-fractures formation. Obviously different from the formation of endo-microfracture, exo-microfracture strongly relates to the coal structure. A good match between the fractures and the pores is needed for a favorable CBM reservoir. Based on the evaluation of pore-fracture system, Yangquan is the second CBM commercial area of Qinshui basin.