Numerical modeling and experimental validation of anomalous time and space subdiffusion for gas transport in porous coal matrix

Kang, Jianhong; Zhou, Fang; Xia, Tongqiang; Ye, Gaobang

doi:10.1016/j.ijheatmasstransfer.2016.04.110

Cited by 63 publications

(24 citation statements)

References 37 publications

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“…However, there is no physical basis to justify allowing a spatially uniform diffusion coefficient to decline with time in this context. Jiang et al (2013), Kang et al (2015Kang et al ( , 2016 and Fan et al (2016) alternatively proposed to use time and space-fractional diffusion equations in order to describe gas production curves over the full time range. This more phenomenological approach is driven by the general use of fractional diffusion models for anomalous diffusion processes and does not require transient diffusion coefficients.…”

Section: Introductionmentioning

confidence: 99%

Gas Diffusion in Coal Powders is a Multi-rate Process

2019

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Gas migration in coal is strongly controlled by surface diffusion of adsorbed gas within the coal matrix. Surface diffusion coefficients are obtained by inverse modelling of transient gas desorption data from powdered coals. The diffusion coefficient is frequently considered to be dependent on time and initial pressure. In this article, it is shown that the pressure dependence can be eliminated by performing a joint inversion of both the diffusion coefficient and adsorption isotherm. A study of the log-log slope of desorbed gas production rate against time reveals that diffusion within the individual coal particles is a multi-rate process. The application of a power-law probability density function of diffusion rates enables the determination of a single gas diffusion coefficient that is constant in both time and initial pressure.

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Section: Introductionmentioning

confidence: 99%

Gas Diffusion in Coal Powders is a Multi-rate Process

2019

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“…Analytical solutions for gas phase pressure and water pressure Substituting eqs. (12) and (13) into eq. (8) gets the governing equation for gas-flow:…”

Section: Fractional Darcy Velocity For Fractal Two-phase Flowmentioning

confidence: 99%

“…The gas-water two-phase flow in porous rock matrix is usually non-linear, tortuous and fractal. An anomalous two-phase flow rather than Darcy flow may dominate the process of thermal stimulation enhanced CBM recovery [12]. In addition, the pathway of heat conduction is also anomalous.…”

Section: Introductionmentioning

confidence: 98%

Analytical solutions of fractal-hydro-thermal model for two-phase flow in thermal stimulation enhanced coalbed methane recovery

2019

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Thermal stimulation is a useful supplementary mining technique for the enhancement of coalbed methane recovery. This technique couples the temperature change with gas-water two-phase flow in the mining process. Many integer dimension hydro-thermal models have been proposed but cannot well describe this coupling because two-phase flow and heat conduction are usually non-linear, tortuous and fractal. In this study, a fractal-hydro-thermal coupling model is proposed to describe the coupling between heat conduction and two-phase flow behaviors in terms of fractional time and space derivatives. This model is analytically solved through the fractal travelling-wave method for pore pressure and production rate of gas and water. The analytical solutions are compared with the in-situ coalbed methane production rate. Results show that our proposed fractal-hydro-thermal model can describe both heat and mass transfers in thermal stimulation enhanced coalbed methane recovery.

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“…Because the pore size is the same, the resistance for gas diffusion in the medium will also be equal, so the calculated diffusion coefficient is a constant (Kang et al, 2016;Shahtalebi et al, 2016;Ni et al, 2014).…”

Section: A C C E P T E D Accepted Manuscriptmentioning

confidence: 99%