A numerical approach to upgrade the estimation of gas diffusion coefficient in coal matrix

Peng Liu, Shimin Liu, Guangzhi Yin

Research output: Contribution to conferencePaper

Abstract

Accurately estimating diffusion coefficient of coal is of great significance for coalbed gas production planning. However, the most commonly used approach (written as infinite series) to inverse D may result in erroneous estimation due to assuming a constant surface concentration in solving the Fick diffusion model. This study first conducted a succession of experiments on coal-gas (CH4 and CO2) ad/desorption, and on the basis of Fick diffusion model, both an analytical approach and a numerical approach were proposed to inverse D in coal. The inversion result shows D is not a constant, it increases with pore pressure decreasing. The discrepancy resulted from using distinct inversion approaches varies with the pore pressure changing. It implies using the analytical approach to inverse D will underestimate the gas diffusivity of coal in some extend. Assuming a constant surface concentration will introduce some unpredictable deviation, even some unacceptable error. Finally, a dimensionless processing for Fick diffusion model was proposed to easy the numerical approach to inverse gas diffusion coefficient. This work is expected to make a clear evaluation on the influence of holding a constant surface concentration in solving Fick diffusion model and suggest a high-accuracy and efficient approach to estimate gas diffusion coefficient and model gas transport behaviors in coal matrix.

Original languageEnglish (US)
StatePublished - Jan 1 2019
Event53rd U.S. Rock Mechanics/Geomechanics Symposium - Brooklyn, United States
Duration: Jun 23 2019Jun 26 2019

Conference

Conference53rd U.S. Rock Mechanics/Geomechanics Symposium
CountryUnited States
CityBrooklyn
Period6/23/196/26/19

Fingerprint

gaseous diffusion
Diffusion in gases
Coal
coal
diffusion coefficient
matrix
matrices
gas
production planning
gases
inversions
Pore pressure
porosity
pore pressure
gas transport
Gases
diffusivity
estimating
Coal gas
desorption

All Science Journal Classification (ASJC) codes

  • Geochemistry and Petrology
  • Geophysics

Cite this

Liu, P., Liu, S., & Yin, G. (2019). A numerical approach to upgrade the estimation of gas diffusion coefficient in coal matrix. Paper presented at 53rd U.S. Rock Mechanics/Geomechanics Symposium, Brooklyn, United States.
Liu, Peng ; Liu, Shimin ; Yin, Guangzhi. / A numerical approach to upgrade the estimation of gas diffusion coefficient in coal matrix. Paper presented at 53rd U.S. Rock Mechanics/Geomechanics Symposium, Brooklyn, United States.
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Liu, P, Liu, S & Yin, G 2019, 'A numerical approach to upgrade the estimation of gas diffusion coefficient in coal matrix', Paper presented at 53rd U.S. Rock Mechanics/Geomechanics Symposium, Brooklyn, United States, 6/23/19 - 6/26/19.

A numerical approach to upgrade the estimation of gas diffusion coefficient in coal matrix. / Liu, Peng; Liu, Shimin; Yin, Guangzhi.

2019. Paper presented at 53rd U.S. Rock Mechanics/Geomechanics Symposium, Brooklyn, United States.

Research output: Contribution to conferencePaper

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AU - Liu, Shimin

AU - Yin, Guangzhi

PY - 2019/1/1

Y1 - 2019/1/1

N2 - Accurately estimating diffusion coefficient of coal is of great significance for coalbed gas production planning. However, the most commonly used approach (written as infinite series) to inverse D may result in erroneous estimation due to assuming a constant surface concentration in solving the Fick diffusion model. This study first conducted a succession of experiments on coal-gas (CH4 and CO2) ad/desorption, and on the basis of Fick diffusion model, both an analytical approach and a numerical approach were proposed to inverse D in coal. The inversion result shows D is not a constant, it increases with pore pressure decreasing. The discrepancy resulted from using distinct inversion approaches varies with the pore pressure changing. It implies using the analytical approach to inverse D will underestimate the gas diffusivity of coal in some extend. Assuming a constant surface concentration will introduce some unpredictable deviation, even some unacceptable error. Finally, a dimensionless processing for Fick diffusion model was proposed to easy the numerical approach to inverse gas diffusion coefficient. This work is expected to make a clear evaluation on the influence of holding a constant surface concentration in solving Fick diffusion model and suggest a high-accuracy and efficient approach to estimate gas diffusion coefficient and model gas transport behaviors in coal matrix.

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Liu P, Liu S, Yin G. A numerical approach to upgrade the estimation of gas diffusion coefficient in coal matrix. 2019. Paper presented at 53rd U.S. Rock Mechanics/Geomechanics Symposium, Brooklyn, United States.