Permeability evolution and mesoscopic cracking behaviors of liquid nitrogen cryogenic freeze fracturing in low permeable and heterogeneous coal

Yin, Guangzhi; Shang, Delei; Li, Minghui; Huang, Jie; Gong, Tiancheng; Song, Zhenlong; Deng, Bangming; Liu, Chao; Xie, Zhicheng

doi:10.1016/j.powtec.2017.10.058

Cited by 63 publications

(22 citation statements)

References 28 publications

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“…Coal seams are heterogeneous, and the permeability of some areas is slightly good and the permeability of some areas is poor (Moore et al., 2015; Peng et al., 2017; Yin et al., 2018). After addition of water invades into the coal seam, the displaced methane can easily flow out through coal seam fractures to a region with a slightly good permeability.…”

Section: Engineering Application Of Isobaric Imbibitionmentioning

confidence: 99%

Dynamic response characteristics of water and methane during isobaric imbibition process in remolded coal containing methane

Yue

Wang

Chen

2018

Energy Exploration & Exploitation

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Addition of water to the coal is actually an isobaric imbibition process. To study the dynamic response characteristics of water and methane, the isobaric imbibition process was stimulated by a self-designed experimental device which can eliminate the reabsorbing phenomenon. The results indicate that adding water can displace absorbed gas. The displacement mechanism is attributed to the capillary effect and competitive adsorption during isobaric imbibition process. A competitive adsorption phenomenon exists between gas molecules and water molecules. Since oxygen-containing functional groups in coal and the hydrogen bond of water, water can easily occupy high-energy sites and only the low-energy sites are available for methane. The imbibition quantity increases with increasing water content or adsorption equilibrium pressure. Moreover, the imbibition quantity would reach a maximum value. The relationship between water content and maximum imbibition quantity or the maximum imbibition rate can be described by a Langmuir function under the same adsorption equilibrium pressure. The maximum imbibition quantity increases with increasing adsorption equilibrium pressure under the same water content, which also can be described by a Langmuir function. However, the maximum imbibition rate decreases with increasing adsorption equilibrium pressures under the same water content, which can be described by an exponential function. Compared to the adsorption equilibrium pressure, the water content has a greater effect on the imbibition quantity and imbibition rate. This study revealed the mechanisms of the dynamic response characteristics of water and methane during

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Section: Engineering Application Of Isobaric Imbibitionmentioning

confidence: 99%

Dynamic response characteristics of water and methane during isobaric imbibition process in remolded coal containing methane

Yue

Wang

Chen

2018

Energy Exploration & Exploitation

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“…At present, most scholars mainly focus on CT scanning to restore the distribution of pore fissures in coal rock [22][23][24]. Few studies have been performed on the multiscale characterization and modelling of coal [25,26], the seepage flow law of water in real pores and the dynamic seepage evolution mechanism [27][28][29].…”

Section: Introductionmentioning

confidence: 99%

Reconstruction and seepage simulation of a coal pore-fracture network based on CT technology

Jing

Meng

Ge³

et al. 2021

PLoS ONE

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The distribution of multiscale pores and fractures in coal and rock is an important basis for reflecting the capacity of fluid flow in coal seam seepage passages. Accurate extraction and qualitative and quantitative analysis of pore-fracture structures are helpful in revealing the flow characteristics of fluid in seepage channels. The relationship between pore and fracture connectivity can provide a scientific reference for optimizing coal seam water injection parameters. Therefore, to analyse the change in permeability caused by the variability in the coal pore-fracture network structure, a CT scanning technique was used to scan coal samples from the Leijia District, Fuxin. A total of 720 sets of original images were collected, a median filter was used to filter out the noise in the obtained images, and to form the basis of a model, the reconstruction and analysis of the three-dimensional pore-fracture morphology of coal samples were carried out. A pore-fracture network model of the coal body was extracted at different scales. Using the maximum sphere algorithm combined with the coordination number, the effect of different quantitative relationships between pore size and pore throat channel permeability was studied. Avizo software was used to simulate the flow path of fluid in the seepage channels. The change trend of the fluid velocity between different seepage channels was discussed. The results of the pore-fracture network models at different scales show that the pore-fracture structure is nonuniform and vertically connected, and the pores are connected at connecting points. The pore size distribution ranges from 104 μm to 9425 μm. The pore throat channel length distribution ranges from 4206 μm to 48073 μm. The size of the coordination number determines the connectivity and thus the porosity of the coal seam. The more connected pore channels there are, the larger the pore diameters and the stronger the percolation ability. During flow in the seepage channels of the coal, the velocity range is divided into a low-speed region, medium-speed region and high-speed region. The fluid seepage in the coal seam is driven by the following factors: pore connectivity > pore and pore throat dimensions > pore and pore throat structure distribution. Ultimately, the pore radius and pore connectivity directly affect the permeability of the coal seam.

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“…After LN 2 freezing-thaw cycles, they found that the coal specimens' elastic moduli, uniaxial compressive strengths (UCSs) and longitudinal wave velocities dropped while the porosities and Poisson's ratios increased. Yin et al [11] studied the permeability evolution and mesoscopic cracking behavior of coal under LN 2 cooling treatments, and found that the coal permeability and fracture expansion increased with increase in water content. Furthermore, Zhao et al [12] studied the damage effect of LN 2 cooling on fracture propagation in coal by using wet and dry coal specimens.…”

Section: Introductionmentioning

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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Permeability evolution and mesoscopic cracking behaviors of liquid nitrogen cryogenic freeze fracturing in low permeable and heterogeneous coal

Cited by 63 publications

References 28 publications

Dynamic response characteristics of water and methane during isobaric imbibition process in remolded coal containing methane

Dynamic response characteristics of water and methane during isobaric imbibition process in remolded coal containing methane

Reconstruction and seepage simulation of a coal pore-fracture network based on CT technology

Microcrack evolution and permeability enhancement due to thermal shocks in coal

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