Pore structure and multifractal analysis of coal subjected to microwave heating

Li, He; Shi, Shiliang; Lu, Jiexin; Ye, Qing; Lü, Yi; Zhu, Xiangnan

doi:10.1016/j.powtec.2019.02.009

Cited by 175 publications

(59 citation statements)

References 68 publications

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“…The control equation of the gas flow field can be derived by the combination of Equations (13)(14) and (22)(23).…”

Section: Mathematical Modelmentioning

confidence: 99%

“…It is well‐known that the methane generated in coal seams is an efficient and clean source of energy . In recent years, coalbed methane (CBM) development has received special attention in areas with multiple coal seams . Several unconventional gas resources located in coal deposits have been studied as systems .…”

Section: Introductionmentioning

confidence: 99%

“…11,12 In recent years, coalbed methane (CBM) development has received special attention in areas with multiple coal seams. [13][14][15][16] Several unconventional gas resources located in coal deposits have been studied as systems. [17][18][19] At present, gas predrainage along coal seam boreholes is mainly used in China, which is also an effective method for coal seam gas recovery and gas disaster prevention and control in coal mines, [20][21][22] as shown in Figure 2.…”

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confidence: 99%

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Theoretical, numerical, and experimental analysis of effective extraction radius of coalbed methane boreholes by a gas seepage model based on defined criteria

Wang

Chang

et al. 2019

Energy Science & Engineering

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The effective extraction radius of borehole is the main parameter for determining the design and layout for coalbed methane extraction. This paper is aimed at the problem that the criteria and calculation methods for the effective extraction radius of coal seams are not comprehensive. With Wudong Coal Mine in China taken as an example, the critical gas pressure (0.441 MPa) for the calculation of effective extraction radius is first defined. Next, the gas seepage unit model around the borehole is developed, and the theoretical mathematical expression to calculate the effective extraction radius is derived. Then, the numerical simulation of gas extraction is carried out through a computational fluid dynamics program, and the effective extraction radius is obtained numerically. Furthermore, the influence of original gas pressure, borehole diameter, and negative pressure of gas extraction on gas extraction is analyzed. Finally, the results from the theoretical calculation and numerical simulation are validated by the field engineering measurement and the average relative error is small (less than 10%). The results indicate that the effective extraction radius has a linear relationship with the extraction time. Moreover, it is found that the original gas pressure is the main factor affecting the effective extraction radius and the effective extraction radius is proportional to the borehole diameter and negative pressure through analysis. Therefore, the above findings can provide a theoretical basis for determining parameters such as borehole spacing and extraction time of gas extraction in coal mines.

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“…The control equation of the gas flow field can be derived by the combination of Equations (13)(14) and (22)(23).…”

Section: Mathematical Modelmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

mentioning

confidence: 99%

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Theoretical, numerical, and experimental analysis of effective extraction radius of coalbed methane boreholes by a gas seepage model based on defined criteria

Wang

Chang

et al. 2019

Energy Science & Engineering

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“…Due to the complexity of the HM model, the following assumptions are adopted: (a) coal seam is assumed as a dual‐porosity (fractures and matrix pores) single‐permeability elastic medium; (b) the free gases conform to the ideal gas law, and they exist and migrate in the space of fractures and pores; (c) the adsorbed gas exists on the surface of pores, and water only migrates in fractures; (d) for the transport of methane, it first desorbs from the surface of matrix pores—Langmuir equation, then diffuses from the pores to the fractures—Fick's law, and finally seepages from fractures to drainage borehole—Darcy's law; while for the injected flue gas, the transport direction is opposite—gas mixture first seepages from the injection borehole to the fractures, then diffuses from the fractures to the matrix, followed by the competitive adsorption with CH 4 on pore surfaces. The mass transport of gas and water mixture in the process of flue gas enhanced drainage is shown in Figure .…”

Section: Mathematical Model For Flue Gas Enhanced Coal Seam Gas Drainagementioning

confidence: 99%

Numerical investigation of flue gas injection enhanced underground coal seam gas drainage

Huo

Jing

Fan

et al. 2019

Energy Science & Engineering

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Coal seam with low permeability is widely distributed in China. Injection of flue gas (N2:CO2 = 0.85:0.15) is an effective approach to improve coal seam gas drainage efficiency. This process relates complex responses among ternary gases (CH4, CO2, and N2) competitive sorption on coals, gas diffusion, gas‐water migration by means of two‐phase flow, and coal deformation. In this paper, an improved hydraulic‐mechanical model coupling above interactions is established for flue gas injection enhanced gas drainage. This model is used to simulate flue gas enhanced drainage by finite element method. The sensitivity analyses of key factors are made to recovery a better understanding on the processes controlling flue gas enhanced drainage. Results show that the flue gas enhanced drainage can indeed improve the efficiency of gas extraction and reduce the gas pressure to the required value in a shorter duration. Due to the competitive adsorption and gas sweeping effect of injected flue gas, CH4 is driven toward drainage borehole, and CH4 pressure and content near the injection borehole decrease faster than that near the drainage borehole. The peak CH4 pressure laterally moves from the injection borehole to the drainage borehole. Higher injection pressure, initial permeability, and smaller sorption affinity ratios may lead to greater CH4 production rate at early drainage stage, but smaller CH4 production rate at late stage. The factors controlling the behavior of flue gas enhanced drainage are initial permeability, injection pressure, and sorption affinity ratios in order. This work offers useful framework to investigate important technical challenges associated with enhanced mine gas drainage, as well as unconventional gas development.

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“…Coal is a complex porous medium that contains an extremely uneven distribution of pores and fractures 20–24 . Coal permeability is affected not only by scale effect and stratification but also by ground stress, gas pressure, matrix sorption‐induced deformation, and temperature.…”

Section: Introductionmentioning

confidence: 99%

Coal permeability evolution characteristics: Analysis under different loading conditions

et al. 2020

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The drainage and utilization of coalbed methane (CBM) resources can not only ensure the safe production of coal mines but also can reduce greenhouse gas emissions and protect the environment. Coal permeability is the key factor that affects the CBM drainage efficiency. To understand the coal permeability evolution characteristics, coal specimens reconstituted by coal powder with different particle sizes were prepared and their permeability under loading conditions was investigated. The results indicate that the coal permeability evolution laws measured by different gases are completely different under constant hydrostatic pressure conditions due to the influence of effective stress and the coal matrix sorption-induced deformation. Under constant effective stress conditions, the helium permeability of coals is almost unchanged if the effects of the Biot's coefficient of coals are ignored, but the methane permeability of coals decreases with increasing gas pressure. In the complete stress-strain process, the variation of coal permeability as the axial strain increases at different stages is almost completely different and the coal permeability in the residual plastic flow stage increases by 2.4-71 times, 1.5-39 times, and 2.8-116 times that of the initial state under the different boundary conditions. Furthermore, it is also found that the coal permeability evolution laws are determined by the effective stress, the sorption-induced deformation of coal matrices, and the malconformation of gas adsorption in coals. This study can help us better understand the seepage characteristics of gas in coals and guide the CBM development. C

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Pore structure and multifractal analysis of coal subjected to microwave heating

Cited by 175 publications

References 68 publications

Theoretical, numerical, and experimental analysis of effective extraction radius of coalbed methane boreholes by a gas seepage model based on defined criteria

Theoretical, numerical, and experimental analysis of effective extraction radius of coalbed methane boreholes by a gas seepage model based on defined criteria

Numerical investigation of flue gas injection enhanced underground coal seam gas drainage

Coal permeability evolution characteristics: Analysis under different loading conditions

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