Modeling of multi-field gas desorption-diffusion in coal: A new insight into the bidisperse model

Kai Wang, Yanhai Wang, Chao Xu, Haijun Guo, Zhiyuan Xu, Yifu Liu, Huzi Dong and Yang Ju

Energy, 2023, vol. 267, issue C

Abstract: Gas desorption-diffusion plays a pivotal role in the coalbed methane extraction, CO2 geological sequestration, CO2 enhanced coalbed methane extraction and coal and gas outburst disasters due to the large amount of adsorbed gas in coal seam. It is of great significance to investigate the gas diffusion mechanisms in coal. The traditional bidisperse model considers that the macropores and micropores are in parallel and independent with each other, neglecting the series structures between the macropores and micropores. In this paper, a coupling multi-field gas desorption-diffusion model was constructed, in which the mechanical field, thermal field and gas diffusion field were fully coupled and the parallel and series structures between the macropores and micropores were both considered, then solved with COMSOL Multiphysics software. The isothermal gas desorption-diffusion experiments of coal particles with different coal particle size were carried out, and the experiment data were used to validate our model. The results show that the model proposed in this paper can be simplified into two cases, in which Model Ⅰ is the parallel model, where all the micropores are in parallel with macropores, and Model Ⅱ is the series model, where all the micropores are in series with macropores. Model Ⅰ and Model Ⅱ characterize the gas diffusion process in coal particles in different ways, where the gas diffusion process in micropores is developed from the boundary to the center of the coal particles in Model Ⅰ, while the gas diffusion in micropores at different locations of coal particles is simultaneous, resulting in nearly uniform distribution of gas pressure in the micropores. No matter how complex the pore structure in coal matrix is, it is the combination of the parallel structures and series structures between adjacent pores. The research results of this paper are instructive to the gas diffusion in coal and other fields such as shale gas extraction.

Keywords: Gas diffusion in coal; Bidisperse model; Numerical model; Thermal effects; Multi-field coupling (search for similar items in EconPapers)
Date: 2023
References: View references in EconPapers View complete reference list from CitEc
Citations: View citations in EconPapers (8)

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Persistent link: https://EconPapers.repec.org/RePEc:eee:energy:v:267:y:2023:i:c:s0360544222034211

DOI: 10.1016/j.energy.2022.126534

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