Study on the behavior and mechanism of methane desorption-diffusion for multi-scale coal samples under multi-temperature conditions

Zhao, Dong; Li, Xiaowei; Feng, Zengchao; Pu, Yuxin; Chang, Haiming; Jia, Yunyi

doi:10.1016/j.fuel.2022.125332

Cited by 21 publications

(5 citation statements)

References 37 publications

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“…However, H-values were positively correlated with the total organic carbon (TOC) content and the equilibrium methane adsorption capacity (SP 0.5 MPa ) of the samples in a statistically significant manner with correlation coefficients of 0.75 and 0.78, respectively, and P-values less than 0.01. It shows that the adsorption effect decreases the diffusivities of methane, and the greater the adsorption amount, the more noticeable the adsorption effect's suppression effect on methane diffusion, which is consistent with the study by Zhao et al 15 4.3. Stress−Adsorption Coupling Effects on Methane Diffusivities.…”

Section: Effect Of Adsorption On the Diffusion Of Methanementioning

confidence: 99%

“…The gas-in-place content and migration ability are critical for developing and evaluating shale gas. − The pores in shale can be classified into two categories: microfractures and matrix pores, and gas follows different migration mechanisms in these two types of pore structures . In microfractures, laminar flow is the primary mechanism, driven by the fluid pressure gradient, and can be described by Darcy’s law and the Hagen–Poiseuille equation or by first-order or second-order slip equations considering the slip effect. − In matrix pores, diffusion mainly dominates fluid transport, as described by Fick’s law. , The effective diffusion coefficient in the matrix is influenced by factors such as matrix pore size, oil–water saturation, and methane adsorption effects. , Among them, the adsorption expansion effect is the focus of research; methane adsorption is generally believed to reduce the pore size, thereby reducing the effective diffusion coefficient. − …”

Section: Introductionmentioning

confidence: 99%

“… 11 , 12 Among them, the adsorption expansion effect is the focus of research; methane adsorption is generally believed to reduce the pore size, thereby reducing the effective diffusion coefficient. 13 − 15 …”

Section: Introductionmentioning

confidence: 99%

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Measurement of Gas Diffusion Coefficients in Cores of Fine-Grained Lithologies Considering Stress and Adsorption Effects

Sun,

Zhou,

2023

ACS Omega

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Matrix diffusivity is vital for developing tight sandstone and shale gas reservoirs. This study proposes a method to test the diffusivities of a core under confining pressure conditions using the gas diffusion technique. The diffusivities of methane and helium were examined in fine-grained rocks (sandy shale, silty sandstone, tight sandstone, and shale) under specific stress conditions. The results revealed that the gas diffusivities varied among the samples. The tight sandstones exhibited diffusivity higher than that of silty sandstone, sandy mudstone, and shale. Helium diffusivities in shales and sandy mudstones were 1 order of magnitude smaller, while methane diffusivities were 2 orders of magnitude smaller than those in tight sandstones. A positive correlation was observed between the stress sensitivity factor and the clay mineral content, indicating the influence of the clay minerals’ mechanical properties. Additionally, the shale gas diffusivities exhibited significant anisotropy due to slit-like gas channels parallel to laminae in shale. It was found that the impact of adsorption on diffusivity was positively correlated to the amount of adsorption. While the adsorption effect was negligible in tight sandstones, organic-rich shales and sandy mudstones experienced an order-of-magnitude reduction in methane diffusivities compared to helium. This study presents a method to evaluate the diffusion coefficient of a core matrix under a confining pressure. It provides insights into gas diffusion behavior in different fine-grained rocks, considering the effects of stress, clay mineral content, and adsorption. These findings contribute to understanding tight sandstone gas and shale gas reservoirs, aiding in the optimization of gas production strategies.

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Section: Effect Of Adsorption On the Diffusion Of Methanementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Measurement of Gas Diffusion Coefficients in Cores of Fine-Grained Lithologies Considering Stress and Adsorption Effects

Sun,

Zhou,

2023

ACS Omega

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“…According to the theory of gas molecular motion [57,58], temperature mainly impacts gas molecular diffusion through the root-mean-square speed and average free path of the gas molecules. Molecular motion theory in materials science states that the temperature of a gas is an indicator of the average kinetic energy of the molecules [32,59].…”

Section: Influence Of Temperature On the Diffusion Coefficientmentioning

confidence: 99%

Experimental Study on Methane Diffusion Characteristics of Different Metamorphic Deformed Coals Based on the Counter Diffusion Method

Ren,

Gao,

Wen

et al. 2023

Processes

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The diffusion coefficient (D) is a key parameter that characterizes the gas transport occurring in coal seams. Typically, D is calculated using the desorption curve of particle coal. However, this method cannot accurately reflect the diffusion characteristics under the stress constraint conditions of in situ coal seams. In this study, different metamorphic deformed coals of medium and high coal rank were considered based on Fick’s law of counter diffusion. The change laws of D under different confining pressures, gas pressures, and temperature conditions were tested and analyzed, and the influencing mechanisms on D are discussed. The results showed that D of different metamorphic deformed coals exponentially decreased with an increase in confining pressures, and exponentially increased with increases in gas pressures and temperature. There is a limit diffusion coefficient. The influence of the confining pressure on D can essentially be determined by changes in the effective stress, and D negatively affects the effective stress, similar to permeability. The effect of gas pressure on D involves two mechanisms: mechanical and adsorption effects, which are jointly restricted by the effective stress and the shrinkage and expansion deformation of coal particles. Temperature mainly affects D by changing the root-mean-square speed and average free path of the gas molecules. Under the same temperature and pressure conditions, D first increased and then decreased with an increase in the degree of deformation. D of the fragmented coal was the largest. Under similar deformation conditions, D of the high-rank anthracite was larger than that of the medium-rank fat coal. Porosity is a key factor affecting the change in D in different metamorphic deformed coals.

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“…The temperature varies considerably from mine to mine depending on the mining depth and climatic conditions (Sagha et al 2007;Zhao et al 2022), and it is one of the most vital factors impressing the gas adsorption capacity (Guan et al 2018). The effect of temperature on gases adsorption of coal has been studied by scholars using different research methods.…”

Section: Introductionmentioning

confidence: 99%

Investigation of adsorption-diffusion behaviors of elementary O2, CO2, and N2 in coal particles: influence from temperature

Liu

Chu

et al. 2023

Environ Sci Pollut Res

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Adsorption-diffusion behaviors of gases (i.e., O 2 , CO 2 and N 2 ) in coal are directly related to the coal spontaneous combustion (CSC), in which the temperature is the key factor affecting the gas migration process in coal. In this work, isothermal adsorption experiments of O 2 , CO 2 and N 2 under different temperatures were carried out on bituminous coal and anthracite coal samples at 0.5 MPa, respectively. Based on the free gas density gradient diffusion (FDGD) model, the microchannel diffusion coe cients of different gases at different temperatures were calculated, and the effects from temperature were quantitatively evaluated. The results acquired from the experiment and simulation show that (i) the adsorption capacity of these three gases decreases as the temperature increases, and the adsorption capacity at the same temperature satis es CO 2 > O 2 > N 2 ; (ii) the FDGD model is veri ed to be still applicable at high temperatures, indicating that the adsorption-diffusion behavior of O 2 , CO 2 and N 2 in coal particles at different temperatures is still consistent with the free gas density gradient diffusion; (iii) the microchannel diffusion coe cient K m of the three gases gradually increases when the temperature goes up. The present work contributes to the understanding of the gases migration process in the development of CSC.

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Study on the behavior and mechanism of methane desorption-diffusion for multi-scale coal samples under multi-temperature conditions

Cited by 21 publications

References 37 publications

Measurement of Gas Diffusion Coefficients in Cores of Fine-Grained Lithologies Considering Stress and Adsorption Effects

Measurement of Gas Diffusion Coefficients in Cores of Fine-Grained Lithologies Considering Stress and Adsorption Effects

Experimental Study on Methane Diffusion Characteristics of Different Metamorphic Deformed Coals Based on the Counter Diffusion Method

Investigation of adsorption-diffusion behaviors of elementary O2, CO2, and N2 in coal particles: influence from temperature

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