Characteristics of pore development in medium-high rank coal

The adsorption/desorption, diffusion, and migration of CBM are so closely related to the pore development in coals that experimental study on it is very essential. It is a fast, convenient, non-toxic and harmless way to obtain capillary pressure data of coals through centrifugation. The pore structure types in medium-high rank coal are characterized and classified through centrifugation instead of mercury injection and a comparison is made between the two methods. Meanwhile, the origin of pore development is explored with SEM experiment. The result shows:pore structure in coals can be classified into three types according to the coal rank. From typeⅠto type Ⅲ, the pore development transits from macro-pores to micro-pores and the storage and transportation mode for CBM from adsorption and diffusion to free seepage. Centrifugation and mercury injection are similar in characterizing the pore development. Various kinds of pore origin in coal lead to the differences in the storage and transportation mode for CBM.