Dynamical modeling of coupled heat and mass transfer process of coalbed methane desorption in porous coal matrix

Kang, Jianhong; Zhu, Jiachen; Wang, Youpai; Zhou, Fang; Liu, Yingke

doi:10.1016/j.ijheatmasstransfer.2021.122212

Cited by 12 publications

(8 citation statements)

References 39 publications

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“…Many key parameters in coal reservoir such as permeability, gas content, stress and temperature change dynamically during CBM recovery, which involves the complex intercoupling of multiple fields [ [28] , [29] , [30] ]. For example, gas desorption from coal matrix is endothermic, which causes decrease of reservoir temperature [ 31 ], meanwhile the decrease of reservoir temperature improves the gas adsorption capacity of the matrix [ [32] , [33] , [34] ]. Based on the physical model of coal, several mathematical models for CBM recovery have been derived currently [ [35] , [36] , [37] ].…”

Section: Introductionmentioning

confidence: 99%

Investigation on the influence of the macropores in coal on CBM recovery

Liu,

Sang,

Zhou

et al. 2023

Heliyon

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Section: Introductionmentioning

confidence: 99%

Investigation on the influence of the macropores in coal on CBM recovery

Liu,

Sang,

Zhou

et al. 2023

Heliyon

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“…Desorption refers to the process by which movable gas molecules in organic matter (OM) are removed from the OM’s inner surface and transformed into the free phase as a result of changes in the temperature, pressure, and other physical conditions of the molecules, which increase the energy of thermal motion and overcome the gravitational field. , This process can be quantitatively characterized by physical experiments and molecular simulation . The 3-fold fracture and pore construction of coal seams determines the characteristics of the CBM desorption stages.…”

Section: Introductionmentioning

confidence: 99%

CBM Desorption Model and Stages Based on a Natural Desorption Experiment

Zhang¹,

Wang

Cui

2022

ACS Omega

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Coalbed methane (CBM) desorption modeling is critical for understanding CBM desorption mechanisms and objectively analyzing the production characteristics of CBM wells. According to the CBM natural desorption experimental data of 64 coal samples taken from the Qinshui Basin, we established a CBM desorption model, quantitatively identified the CBM desorption stages, and discussed the relationship between CBM desorption characteristics and well productivity. The results indicated a very significant functional relationship between the CBM natural desorption time and cumulative desorption quantity, which could be accurately described by the model V = a L t/(t + b L ). On the basis of this model and the numerical description of the desorption data, the CBM natural desorption process was divided into four stages: the desorption startup stage, desorption sensitive stage, desorption steady stage, and desorption decay stage. As indicated by analogical reasoning of the CBM well production process, the desorption startup stage corresponded to the drainage-based pressure drop stage, the desorption sensitive and steady stages corresponded to the steady production stage, and the desorption decay stage corresponded to the production declining stage. The CBM adsorption time exponentially decreased with the increase in the average CBM desorption rate and with the increase in the CBM gas content and vitrinite/inertinite ratio. Furthermore, within a certain range of desorption pressure, a high ratio between the adsorption time and gas content corresponded to the extension of the steady production stage of CBM wells, whereas higher or lower ratios were adverse to steady production.

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“…For instance, the classical unipore diffusion model (UDM) based on Fick’s second law, which asserts that gas desorption and diffusion are driven by a concentration gradient in which the diffusion coefficient is assumed as a constant value . The predicted UDM results deviated significantly from the experimental measurements, while the gas diffusion volume cannot be correctly estimated with a constant diffusion coefficient. , To improve such an estimation, bidisperse diffusion models (BDMs) , and various time-dependent diffusivity models (TDDMs) − were proposed from the spatial and temporal domains, respectively; however, some of them may have complex forms, unclear physical meanings, and are inconvenient to predict the late CBM production. , Moreover, an anomalous subdiffusion model with fractional time and space emerged can somehow guarantee the simulation accuracy, while there are significant challenges in their modeling solution work. , In addition, employing Darcy’s law (pressure gradient driven) to describe gas diffusion is also questionable under certain conditions . Accordingly, we previously demonstrated that the gas diffusion flow in a coal matrix is driven by the free gas density gradient (FGDG) and then developed a FGDG model (FGDGM), assuming that free gas is the main contributor to the gas flow and that the diffusive mass flux is proportional to the FGDG.…”

Section: Introductionmentioning

confidence: 99%

“…24,34 Moreover, an anomalous subdiffusion model with fractional time and space emerged can somehow guarantee the simulation accuracy, while there are significant challenges in their modeling solution work. 35,36 In addition, employing Darcy's law (pressure gradient driven) to describe gas diffusion is also questionable under certain conditions. 26 Accordingly, we previously demonstrated that the gas diffusion flow in a coal matrix is driven by the free gas density gradient (FGDG) and then developed a FGDG model (FGDGM), 37 assuming that free gas is the main contributor to the gas flow and that the diffusive mass flux is proportional to the FGDG.…”

Section: Introductionmentioning

confidence: 99%

Modeling of Gas Desorption and Diffusion Kinetics in a Coal Seam Combined with a Free Gas Density Gradient Concept

Qin

Yang

et al. 2022

Energy Fuels

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Gas diffusion in a coal seam plays an essential role in the efficient and effective exploitation of underground coalbed methane (CBM). Based on the concept of free gas density gradient-driven flow, in this work, we formulated and validated a theoretical model to quantify gas desorption and diffusion kinetics in a coal seam at different temperatures. Once the governing equations are formulated and non-dimensionalized, they are numerically solved with the finite difference method and then validated with the experimental measurements on gas desorption at different temperatures. The mechanism of temperature affecting gas diffusion kinetics was elaborately explored. Also, the advantages of the proposed free gas density gradient model (FGDGM) compared to the traditional unipore diffusion model (UDM) were well evaluated and discussed. It is found that the FGDGM simulations are basically consistent with the experimental data, but the UDM prediction deviates significantly from the experimental measurements at different temperatures. By introducing a new dimensionless temperature variable and performing sensitivity analysis, the dimensionless gas desorption is found to increase with temperature, while the incremental gas desorption varies across the entire temperature range. With the temperature increasing from 293 to 313 K, both the gas desorption increment and gas yield enhancement are found to be the largest. In addition, there exists a linear relationship between diffusivity and temperature because a high temperature increases the gas molecules’ activity and accelerates the pore expansion. It is clearly found that temperature has a considerable contribution to the gas diffusion kinetics in a coal seam, and appropriately boosting the coal temperature to enhance CBM recovery is feasible and valuable.

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Dynamical modeling of coupled heat and mass transfer process of coalbed methane desorption in porous coal matrix

Cited by 12 publications

References 39 publications

Investigation on the influence of the macropores in coal on CBM recovery

Investigation on the influence of the macropores in coal on CBM recovery

CBM Desorption Model and Stages Based on a Natural Desorption Experiment

Modeling of Gas Desorption and Diffusion Kinetics in a Coal Seam Combined with a Free Gas Density Gradient Concept

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