The seepage properties and permeability enhancement mechanism in coal under temperature shocks during unloading confining pressures

Wang, Dengke; Zhang, Ping; Wei, Jianping; Yu, Chong

doi:10.1016/j.jngse.2020.103242

Cited by 38 publications

(18 citation statements)

References 27 publications

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“…In the process of coal seam excavation, the balance state of in-situ stress and gas pressure of coal body is destroyed, and the coal body around the roadway forms pressure relief zone, stress concentration zone and original stress zone from the outside to the inside. Due to the change of coal body stress, the physical characteristics of coal body are changed, and the parameters such as permeability and gas pressure show obvious differences 23 , 30 . The intensity of gas emission and the form of gas flow field in coal seam are very different in different positions.…”

Section: Analysis Of the Methods Of Calculation Of The Size Of The Gas Emission Zonementioning

confidence: 99%

A calculation method of gas emission zone in a coal mine considering main controlling factors

Chen

Liu

Xuan

2021

Sci Rep

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The gas emission zone is an important parameter for the space–time effect of coal excavation and gas emission. In this paper, according to the effect of roadway excavation, a numerical model of gas emission zone based on the evolution of stress and permeability was established to obtain the width of gas emission zone with different pressure and permeability coefficient. Then the numerical simulation results were verified by measuring the gas content at different depths. Through numerical simulation and field measured data, the theoretical calculation formula is established on the basis of comprehensive consideration of the influencing factors of gas emission zone. The results showed that the gas emission zone increases with the increase of coal seam gas pressure and permeability coefficient when the roadway section and exposure time are the same. The measured gas emission zone, when taking gas content as the index with the same logistic function growth curve, matches the measured results with a relative error of 1.3 to 6%. The validity of the model is also verified by field experiments. The results can provide guidance for mine gas emission and gas drainage design.

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Section: Analysis Of the Methods Of Calculation Of The Size Of The Gas Emission Zonementioning

confidence: 99%

A calculation method of gas emission zone in a coal mine considering main controlling factors

Chen

Liu

Xuan

2021

Sci Rep

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“…On this basis, different confining pressures are applied to coal mass after temperature impact. The seepage of coal under different confining pressures after temperature impact can be analyzed with the gas permeability experimental device combined [29]. Supercritical CO2 fracturing has a similar effect to hydraulic fracturing.…”

Section: Research Of Mechanical Properties Of Coal Damagementioning

confidence: 99%

Application and development of CT scanning technology in coal sector

et al. 2021

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CT scanning technology has been widely used in the observation of coal microstructures because of its advantages of non-destructive and refined visualization. In this study, the post-processing methods (image processing, 3D reconstruction, numerical simulation, etc.) of CT scan images are introduced in detail, and the application of CT in the coal sector is systematically reviewed, mainly including: coal seam gas mining (coal structure, reservoir permeability etc.); mechanical properties of coal mass damage; coal seam water injection, coal mass permeability enhancement, coal washability, etc. The application of CT in various research fields has been relatively mature. The initial research is focused on the analysis of coal mass structure, and subsequently the fractal dimension is introduced and the in-depth study of coal mass seepage is involved. At the same time, CT scanning equipment is been constantly improving to be applied to a wider range of explorations. In the future, improved image processing or equipment can increase the research accuracy, and the field of coal structure and seepage under the multi-field coupling conditions such as pressure-temperature-seepage can be explored.

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“…Studies have that once thermal stress caused by thermal shocks in coal specimens exceeds coal peak strength, crack propagation and coal failure occur [63,64]. To explain the propagation and growth of microcracks in Figs 6, 7, 8 and 9, it is imperative to determine the stress field near the crack tips and the failure conditions of microcracks.…”

Section: Crack Propagation Criterion Of Coalmentioning

confidence: 99%

Microcrack evolution and permeability enhancement due to thermal shocks in coal

Zhang

Wang

et al. 2020

PLoS ONE

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To understand the effects of thermal shock on microcrack propagation and permeability in coal, thermal shock tests were conducted on coal specimens by using a constant temperature drying oven (105˚C) and a SLX program controlled cryogenic tank. The growth and propagation of microcracks were measured with computer tomography (CT) scanning and scanning electron microscope (SEM) tests. Results showed that thermal shocks improved the permeability of coal significantly. Notably, the permeability of coal after thermal shocks increased from 211.31% to 368.99% and was positively correlated with temperature difference. CT scanning images revealed that thermal shocks increased the crack number, crack volume and crack width as well as smoothened and widened the gas flow paths, thereby enhancing coal permeability. Moreover, SEM images showed that heating-cooling shocks created more new microcracks, forming more complex crack propagation paths and better connectivity among microcracks in coal compared to cooling shocks. We proposed a crack propagation criterion for coal to explain the mechanism of crack failure and propagation during thermal shocks. Our experiment results and theoretical analysis indicate that the heating-cooling shock is more effective in damaging and breaking coal than the cooling shock. Thus, it can be used as an alternative approach to enhance coal permeability in the production of coalbed methane (CBM).

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The seepage properties and permeability enhancement mechanism in coal under temperature shocks during unloading confining pressures

Cited by 38 publications

References 27 publications

A calculation method of gas emission zone in a coal mine considering main controlling factors

A calculation method of gas emission zone in a coal mine considering main controlling factors

Application and development of CT scanning technology in coal sector

Microcrack evolution and permeability enhancement due to thermal shocks in coal

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