Microscopic pore structure characteristics of Shanxi Formation coal reservoir in Daning-Jixian Block

Accurate description of micro and nano pores in coal reservoir plays an important role in evaluating the reservoir and gas production capacity of coalbed methane, we used 6 continuous samples of high rank coal in Daning-Jixian area on the eastern margin of Ordos Basin as the research object, and combined with high pressure mercury injection, low temperature N₂ adsorption and low pressure CO₂ adsorption experiments to characterize the pore structure characteristics. The aim of this study is to have an in-depth understanding of the full-size pore size distribution and explore the influencing factors of coal reservoir pore structure. The results show that the pore volume and specific surface area of coal sample in the study area have obvious differences with the pore size distribution, and the contribution rate of coal sample micropores to pore volume and specific surface area is significant, especially the diameter <1.5 nm micropore provides storage space for most of the adsorptive gas. The contribution of mesoporous and macroporous to pore volume and surface area is relatively small, which is not conducive to coalbed methane seepage. The vitrinite content of coal samples in the study area is positively correlated with pore volume and specific surface area, which contributes significantly to pore development. The relationship between inertinite content and pore volume and surface area is not obvious. With the increase of M_ad, more adsorption pores are developed in coal samples, and pore volume and specific surface area are negatively correlated with A_d, indicating that the increase of A_d will lead to the decrease of pore volume and specific surface area.