Preservation and deliverability characteristics of coalbed methane, North China

One hundred and forty-four coal samples from 9 coalfields (or coal basins) in North China were examined using the microfracture analysis by fluorescence microscope, liquid nitrogen adsorption analysis and mercury-injection analysis. Microfractures in coals arc dominantly less than 5 μm wide and less than 300 J/m long, and frequency is about 20-200 strips per 9 cm2. Porosity of the coals ranges from 2.38% to 10.3%, and is mainly of adsorption-pore (pore size less than 100 nm) which is favorable for adsorption and accumulation of gas, but unfavorable for desorption and recovery of gas. Accumulation ability is best in Jiaozuo, Xinggong, secondarily in Pingdingshan. Datong, south Qinshui, and followed by others, while deliverability is best in Huainan-Huaibei, Pingdingshan. Anhe, and worst in Yongxia and Datong. Poor-developed microfractures in Jiaozuo, poor connectivity in Xinggong. and low proportion of seepage-flow pores (pore size larger than 100 nm) in Qinshui bring about 'bottleneck problems' for the recovery of coalbed methane.