Meitan xuebao (Aug 2023)
Effects of nanoparticle composite surfactants on the adsorption/desorption and diffusion of CH4 in coal
Abstract
A solid (coal) - gas (CH4) - liquid (surfactant) three-phase interaction system model is established based on the Grand Canonical Monte Carlo (GCMC) and Molecular Dynamics (MD) methods. The effects of the nanoparticle composite cationic surfactant CTAB, anionic surfactant SDBS and nonionic surfactant VAEO8 on CH4 adsorption/desorption and diffusion in coal are investigated from the aspects of adsorption configuration, adsorption amount, interaction energy, relative concentration distribution and diffusion coefficient. The results show that the surfactants and nanoparticles are imbibed into coal pores, occupying the adsorption sites of CH4 on the coal surface under the wetting effect and electrostatic action. In the absence of nanoparticles, the anionic surfactant SDBS enhances the hydrophilicity of coal and has the best effect on promoting CH4 desorption. Whereas the cationic surfactant CTAB and nonionic surfactant VAEO8 enhance the hydrophobicity of coal, resulting in a weaker CH4 desorption capacity. Nanoparticles and surfactants act synergistically in reducing solid-liquid interfacial tension, so nanoparticle composite surfactants are better than surfactants without nanoparticles in promoting CH4 desorption. After adding nanoparticles, the electrostatic force and interaction energy of the system are all increased. The CH4 diffusion coefficient in the raw coal system > the CH4 diffusion coefficient in surfactant coal system > the CH4 diffusion coefficient in coal system with nanoparticles composite surfactant. Overall, the mechanism of the influence of nanoparticle composite different types of surfactants on CH4 adsorption and diffusion is clarified from the microscopic point of view, and the study provides a theoretical basis for optimizing fracturing fluid system to improve coalbed methane recovery.
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