A multi-scale model for CO₂ sequestration enhanced coalbed methane recovery

Abstract

This paper presents a multi-scale model to simulate the multicomponent gas diffusion and flow in bulk coals for CO₂ sequestration enhanced coalbed methane recovery. The model is developed based on a bi-dispersed structure model by assuming that coal consists of microporous micro-particles, meso/macro-pores and open microfractures. The bi-disperse diffusion theory and the Maxwell-Stefan approach were incorporated in the model, providing an improved simulation of the CH₄—CO₂/CH₄—N₂ counter diffusion dynamics. In the model, the counter diffusion process is numerically coupled with the flow of the mixture gases occurring within macro-pores or fractures in coal so as to account for the interaction between diffusion and flow in gas transport through coals. The model was validated by both experimental data from literature and our CO₂ flush tests, and shows an excellent agreement with the experiments. The results reveal that the gas diffusivities, in particular the micro-pore diffusivities are strongly concentration-dependent.

Keywords

multi-scale model / gas transport / coal / coalbed methane / CO₂ sequestration

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Higher Education Press and Springer-Verlag Berlin Heidelberg