Abstract:
Hydraulic stimulation, as a pivotal technique for coalbed methane control, is frequently integrated with organic chemical inhibitors to enhance gas drainage efficiency by suppressing methane adsorption through competitive adsorption mechanisms. To explore the modification effects of organic reagents on the physicochemical properties of coal and the mechanisms influencing methane adsorption kinetics due to organic components, experiments were conducted using organic reagents (DCM, EA, THF, and DMF) to extract organic components from coal samples and modify their pore structure. A comprehensive qualitative and quantitative analysis of the physical and chemical structure of the coal before and after modification was performed using Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM-EDS), Raman spectroscopy (Raman), X-ray photoelectron spectroscopy (XPS), and
13C nuclear magnetic resonance (
13C-NMR characterization techniques), along with low-pressure N
2 and low-temperature CO
2 fluid invasion methods for pore distribution testing. The study investigates the impact mechanism of the modified coal on methane adsorption through calculations based on an integrated optimization model of micropore filling. The results indicated that the extraction process led to varying degrees of change in the organic components of high-metamorphic bituminous coal, with DMF showing the strongest effect. The relative content of oxygen-containing functional groups significantly decreased, resulting in reduced methane adsorption capacity of the coal (from 26.536 4 cm³/g in the control group to 10.983 0 cm³/g after DMF treatment). Additionally, the extraction process altered the pore structure of the coal, increasing the relative amount of mesopores and macropores while decreasing micropores. The mechanism behind the decrease in adsorption capacity due to chemical factors was elucidated by optimizing the micropore filling theory. Concurrently, molecular dynamics simulations were employed to quantitatively assess the confinement effects in extraction-modified coal systems
via radial distribution function (RDF) analysis. This approach revealed the intrinsic relationship between micropore-filling behavior and the reorganization of organic components, providing a microscopic chemical interpretation of methane adsorption propensity within the coal matrix.