Effects of Pore Structures of Different Maceral Compositions on Methane Adsorption and Diffusion in Anthracite

The pore structure of coal reservoirs is the main factor influencing the adsorption-diffusion rates of coalbed methane. Mercury intrusion porosimetry (MIP), low-pressure nitrogen adsorption (LP-NA), low-pressure carbon dioxide adsorption (LP-CA), and isothermal adsorption experiments with different macerals were performed to characterize the comprehensive pore distribution and methane adsorption-diffusion of coal. On the basis of the fractal theory, the pore structures determined through MIP and LP-NA can be combined at a pore diameter of 100 nm to achieve a comprehensive pore structural splicing of MIP, LP-NA, and LP-CA. Macro-mesopores and micro-transitional pores had average fractal dimensions of 2.48 and 2.18, respectively. The Langmuir volume (V-L) and effective diffusion coefficients (D-e) varied from 31.55 to 38.63 cm(3)/g and from 1.42 to 2.88 x 10(-5) s(-1), respectively. The study results showed that for super-micropores, a higher vitrinite content led to a larger specific surface area (SSA) and stronger adsorption capacity but also to a weaker diffusion capacity. The larger the average pore diameter (APD) of micro-transitional pores, the stronger the diffusion capacity. The diffusion capacity may be controlled by the APD of micro-transitional pores.