Study on pore structure of coal in south Shilou Block and its influence on methane adsorption characteristics

The development degree of pore structure in coal reservoir controls the adsorption performance of methane in coal. Taking the No.2 and No.3 coals in the south Shilou Block as the research objects, the pore structure characteristics of the coals were quantitatively characterized by experimental methods such as low-temperature N₂ adsorption, low-field nuclear magnetic resonance and micro-CT. Based on the methane isotherm adsorption experiment, the changing trend of methane adsorption was obtained, and the relationship between the pore structure of coal and methane adsorption was analyzed. The results show that the pore characteristics of SX-2 coal and SX-3 coal are significantly different. The number of micropores in SX-3 coal is significantly greater than that of SX-2 coal, and its adsorption capacity is better than that of SX-2 coal. There are many cylindrical pores and ink bottle pores in coal, with BET pore specific surface area ranging from 0.608 5 to 2.115 5 m²/g, BJH pore volume ranging from 0.002 6 to 0.005 1 cm³/g, and average pore diameter ranging from 9.643 1 to 17.091 2 nm. The mineral content of coal is significantly higher than that of SX-3 coal. The pore volume and pore specific surface area of coal are negatively correlated with the mineral content in coal. The T₂ spectrum of SX-2 coal shows a trimodal distribution, while that of SX-3 coal shows a bimodal distribution. The pore space distribution of SX-3 coal sample is more concentrated, and the pore connectivity is better. The pore structure of SX-2 coal is mainly macropores, and the pore structure of SX-3 coal is mainly micropores. The microcrack volume of the two coals is mainly provided by cracks with a size greater than 1 000 μm. The volume of microcracks in SX-2 coal is significantly smaller than that in SX-3 coal. The Langmuir model can well describe the adsorption behavior of coal in the study area. Micropores play a leading role in the adsorption of methane. The Langmuir volume is negatively associated with the mineral content in coal, and has a positive correlation with the pore specific surface area and pore volume of coal. The adsorption of methane by SX-3 coal is better than that by SX -2 coal, and the Langmuir volume of SX-3 coal is 2.1 times that of SX-2 coal sample.