Mechanism of extraction modification on multiscale pore structure and methane adsorption kinetics in coal

WANG Liang; ZHENG Siwen; FU Shenguang

doi:10.13225/j.cnki.jccs.2024.0955

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 or-ganic reagents(DCM,EA,THF,and DMF)to extract organic components from coal samples and modify their pore struc-ture.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 reson-ance(13C-NMR characterization techniques),along with low-pressure N2 and low-temperature CO2 fluid invasion meth-ods 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 extrac-tion 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,result-ing 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 sim-ulations were employed to quantitatively assess the confinement effects in extraction-modified coal systems via radial dis-tribution 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.