Characteristics of high-rank coal structure parallel and perpendicular to the bedding plane via NMR and X-ray CT

Pores and fractures and their connectivity play a significant role in coalbed methane production.To investigate the growth characteristics and connectivity of pores and fractures in coal parallel and perpendicular to the bedding plane,the pores and fractures of high-rank coal samples collected from the southern Qinshui Basin were measured by low-field nuclear magnetic resonance,X-ray-computed tomography and field emission scanning electron microscopy.Then,the determinants of their connectivity were further discussed.The results show that the high-rank coal samples have similar pore size distributions both parallel and perpendicular to the bedding plane.They primarily contain mesopores(2-50 nm in width),followed by macrospores(> 50 nm in width).The research indicated that the high-rank coal connectivity parallel to the bedding plane is significantly better than that perpendicular to the bedding plane.The connectivity of high-rank coal is mainly determined by throats,and the orientation of the pores and fractures.The two connectivity modes in high-rank coal are "pore connectivity," in which the throats are mainly pores with a low coordination number,and "microfissure connectivity",in which the throats are mainly microfissures with a high coordination number.