CH4 and CO2 adsorption–desorption-diffusion characteristics in surfactant-modified coal under microscopic conditions

Abstract

Hydraulic techniques are integral to both coal mining and gas extraction procedures, and the precise inclusion of surfactants in hydraulic fracturing fluids serves as a crucial factor influencing the wettability of coal and facilitating gas desorption. Nevertheless, relatively few investigations have focused on the influence of surfactants within coal on the adsorption–desorption-diffusion dynamics of gases. In this study, Xin Tian high-rank coal was treated with different surfactants, and the pore structure and functional groups of the coal samples were determined by fluid invasion methods, Fourier transform infrared (FT-IR) spectroscopy, X-ray photoelectron spectroscopy (XPS), and 13C nuclear magnetic resonance (13C NMR) spectroscopy. Moreover, molecular-scale models were constructed to simulate the adsorption–desorption-diffusion performance of the gases in the surfactant-modified coal. As per the results, modification with methyltrimethoxysilane (MTMS) and polyethylene oxide (PEO) surfactants reduced the proportion of micropores and relative content of oxygen functional groups, resulting in reduced the adsorption of gases and enhanced diffusion performance, consistent with molecular simulations result. These results provide a theoretical foundation for elucidating the adsorption–desorption mechanisms of surfactant-treated coal and its application in mining areas.