| Author's Name: DUAN Yangli1,2, LIANG Xing3, HE Fangyu3, ZHOU Yun3, ZOU Chen3, MEI Jue3,
ZHANG Hanbing1,2, LI Lei1,2, YE Congchen1 |
| Junlian area in the south of Sichuan Basin, as the first commercial production base of coalbed methane in South China,
has a gas producing bed in the Upper Permian Leping Formation, it is great to study the characteristics of micropore structure to
analyze the characteristics of coalbed methane accumulation. In this paper, a large number of Upper Permian Leping coal samples
are selected from coalbed methane evaluation wells for scanning electron microscope observation and liquid nitrogen adsorption
experiments. The characteristics of pore development at micro and nano scale have been systematically analyzed from the aspects of
pore genetic type, pore structure, pore morphology and methane adsorption performance. The results show that micropores of coal
are divided into four genetic types: plant tissue pore, stoma, mineral mold hole and intercrystalline pore. Through quantitative
analysis of pore structure parameter, it is concluded that the average BET total pore specific surface area is 2.638 m2/g, and the
average BJH total pore volume is 0.003 7 cm3/g, and there is a good positive correlation between total pore specific surface area and
total pore volume. The average BJH pore diameter is 5.775~17.842 nm, and the major contribution to the total specific surface area
is from pores with an aperture less than 5 nm, while the major contribution to the total pore volume is from pores greater than 10 nm.
According to the diameter of pores, the pore types are divided into four categories: micropore (＜5 nm), tiny pore (5~10 nm),
mesopore (10~100 nm) and macropore (≥100 nm). Micropores and tiny pores are the main spaces for gas adsorption in high rank
coal, and it is further concluded that the boundary value of pore diameter between adsorption pores and free pores of high rank coal
is 10 nm. Nitrogen adsorption loops are divided into three types (overlap type, semi-separation and semi-overlap slow drop type,
semi-separation and semi-overlap plunge type), and according to the characteristics of the loops, the nanoscale pore morphology is
idealized as three typical models, namely open pore, semi-closed pore and inkbottle-shape pore, and all kinds of pores are
developed in the high rank coal. Based on the comparison of isothermal adsorption experiments of methane from dry ash free coal
samples with different pore morphology, it is found that the adsorption capacity of methane is the highest in inkbottle-shape pores,
and the adsorption capacity of semi-closed and open holes is similar but lower than that of inkbottle-shape pores. |
