Abstract
Gas diffusion-sorption is a critical step in coalbed methane (CBM) exploitation and carbon dioxide sequestration. Because of the particularity of gas physical properties, it is difficult to visualize the gas diffusion-sorption process in coal by experimental methods. Due to the limitation of experimental approaches to image the three-dimensional coal pore structure, it is impossible to obtain the three-dimensional pore structure images of coal. As a result, the visualization of gas diffusion-sorption in coal pore structure by numerical ways is impossible. In this study, gas diffusion coefficients were firstly estimated by experiments. Then, a gas diffusion-sorption coupled model was developed which can be applied to the nanoscale geometry imaged by synchrotron radiation nano-CT. The dynamic process of gas diffusion and ad-/desorption in the nanoscale microstructure of coal was visualized by the developed gas diffusion-adsorption coupled model and the numerical simulation based on MATLAB. The simulation results show a good agreement with the experimental results. The gas diffusion-sorption coupled model and numerical method can help to investigate the effect of microstructure on gas diffusion and ad-/desorption and provides a possibility to investigate the multiscale gas transportation and adsorption in coal pore-fracture system.
Highlights
IntroductionAs a porous medium, exhibits high gas adsorption affinity [1]. As a result, coal is a methane reservoir and can be considered as a potential place for carbon dioxide storage [2, 3]
Coal, as a porous medium, exhibits high gas adsorption affinity [1]
Because there is no capillary condensation in CO2 diffusion tests, which may be caused by the smaller test gas pressure range in CO2 diffusion tests, CO2 diffusion coefficients calculated from the adsorption stage are relatively constant there is a fluctuation with gas pressure (Figure 5(c))
Summary
As a porous medium, exhibits high gas adsorption affinity [1]. As a result, coal is a methane reservoir and can be considered as a potential place for carbon dioxide storage [2, 3]. During coalbed methane (CBM) production, the gas needs to diffuse through the coal matrix and flows to the producing well [6,7,8]. A significant amount of researches has been conducted to study gas diffusion behavior in coal by experimental and numerical methods. Experimental research is focused on the factors that affect gas diffusion behavior, such as particle size [10], temperature [11], and gas pressure [12, 13]. Numerical methods are mainly used to calculate the gas diffusion coefficient by the bidisperse diffusion model [14]. Because the gas pressure in coal matrix is continuously changing during gas production and carbon dioxide sequestration [13]. Methane and carbon dioxide diffusion coefficients during the adsorption and desorption process were measured and comprehensively analyzed. Real-time gas diffusion- sorption process in coal was visualized by the combination of nanoscale microstructure and the coupled model of gas diffusionsorption
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