Comprehensive characteristics of pore structure and factors influencing micropore development in the Laochang mining area, eastern Yunnan, China

Characterization of coal pore structure plays an important role in the exploration and development of coalbed methane. Results from corrected high-pressure mercury injection porosimetry, low-temperature liquid nitrogen adsorption, and low temperature carbon dioxide adsorption were used in combination with fractal theory. This study aims to gain insight into full-scale pore size distribution and to discuss factors influencing micropore development in relation to physical properties of coal samples. The results show that coal compressibility in the study area is between 0.79-1.27 x 10(-10) m(2)/N, the maximum cumulative mercury intrusion volume was 75%-85% of that before correction. Pore shapes are mainly cone pores and parallel plate-shaped pores. The total pore volume (PV) ranges from 0.071-0.084 cm(3)/g. Micropores, especially those with diameters less than 1.5 nm, account for more than 90% of PV, providing storage space for most of the adsorbed gas. The effect of coalification on pore development is complex, there is no obvious relationship between micropore volume, specific surface area (SSA) and coal rank; however, a negative correlation exists between micropore volume, SSA and volatile yield. Moisture and fixed carbon content can increase micropore volume and SSA, while ash yield and minerals tend to reduce micropore volume and SSA.