Nuclear magnetic resonance study of the influence of the liquid nitrogen freeze‐thaw process on the pore structure of anthracite coal

Chu, Yapei; Sun, Haitao; Zhang, Dongming; Guo, Yu

doi:10.1002/ese3.624

Cited by 40 publications

(16 citation statements)

References 41 publications

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“…Affected by various coalification processes, the pore structure in coal has different shapes and sizes, not only rich in micropores and transition pores but also macropores, visible pores, and fractures, which provide a place and channel for gas adsorption, storage, and migration. 39 LNA method is conducive to understanding the nanopore (<100 nm) structure of coal. Therefore, the LNA experiments were conducted with an ASAP2020 specific surface area analyzer (Micromeritics).…”

Section: Low-temperature Nitrogen Adsorption (Lna) Testsmentioning

confidence: 99%

Prediction of methane adsorption capacity in different rank coal at low temperature by the Polanyi‐based isotherm model

Zhao

Wang

et al. 2022

Energy Science & Engineering

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To investigate the adsorption properties of methane in coal under low temperatures, the isothermal adsorption tests of the three coal samples with different metamorphic degrees were conducted at the ambient temperatures of 253.15−293.15 K, and the low‐temperature nitrogen adsorption (LNA) tests of coal were also performed. Then a relational expression of equilibrium pressure, temperature, and methane adsorption capacity (T−P model) was deduced to predict the adsorption isotherm at any other temperature based on the Polanyi adsorption theory. The results show that the gas adsorption capacity of coal can be significantly increased at low temperatures (below 273.15 K), and the adsorbed methane in anthracite is obviously more than that in lean coal and coking coal by the virtue of possessing a larger micropore/transition pore volume and specific surface area. The relations between adsorption potential (ε) and adsorption volume (ω) at different temperatures can be drawn on one single logarithmic curve, and a suitable pseudo‐saturation pressure can be obtained by the improved Amankwah's method. The predicted adsorbed capacities via the T−P model are in line with the measured results at other equilibrium conditions, indicating that the model can contribute to the deep coalbed methane resources estimation and the gas disaster prevention and control in coal mines.

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Section: Low-temperature Nitrogen Adsorption (Lna) Testsmentioning

confidence: 99%

Prediction of methane adsorption capacity in different rank coal at low temperature by the Polanyi‐based isotherm model

Zhao

Wang

et al. 2022

Energy Science & Engineering

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“…The relationship between the transverse relaxation time and pore radius can be expressed as follows: where T 2 is the transverse relaxation time (ms), ρ is the transverse surface relaxation strength (μm/ms), of which the value depends on the mineral composition of the pore surface and the hydrogen-containing nature of the fluid in the pore, and S and V represent the pore surface area (μm 2 ) and pore volume (μm 3 ), respectively. F s is the pore shape factor (spherical pore, F s = 3; columnar pore, F s = 2), r is the pore radius (μm), and C is the pore conversion coefficient (μm/ms), 6 which is a constant related to pore surface relaxation.…”

Section: Experimental Principle and Schemementioning

confidence: 99%

“… 3 − 5 How to improve the permeability of low-permeability coal bed is the key problem to strengthen gas extraction and prevent gas disaster. The pore-fissure system in coal is the main channel for gas flow, 6 so the microscopic pore structure of coal is an important factor determining its permeability. 7 − 11 In essence, the factors affecting coal permeability mainly affect penetrability through affecting the micropore structure of coal.…”

Section: Introductionmentioning

confidence: 99%

Effect of Mixed Acid Fluid on the Pore Structure of High Rank Coal and Acid Fluid Optimization

2022

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Acidizing technology is an important means to increase production in oil-gas reservoirs. In recent years, acidizing technology has been widely used to increase the permeability of coal seams to enhance gas extraction, where acidizing fluid is the key factor to determine the permeability improvement effect by acidizing technology. In order to clarify the influence of mixed acid fluid on the pore structure of high rank coal and seek the optimal mixed acid fluid suitable for acidizing and permeability improvement of high rank coal in the Jiaozuo coal mine area. Taking the Jiulishan Mine in the Jiaozuo mining area as an example, low field nuclear magnetic resonance (LFNMR) test and static dissolution test were conducted to obtain the T 2 spectrum, porosity, movable fluid saturation, pore throat distribution, nuclear magnetic permeability, and dissolution rate of coal samples before and after treatment with distilled water and three mixed acid fluids. On this basis, the influence of mixed acid fluid on the pore structure of high rank coal was analyzed and the optimal mixed acid fluid suitable for high rank coal was selected. The results showed that the pore size, number, and volume of all kinds of pore sizes of coal samples treated with distilled water all decreased, which was manifested by the decrease of effective porosity and nuclear magnetic permeability. After acidification, the proportion of micropore volume in coal decreased significantly, the number and proportion of pore volume of mesopores and macropore-microfractures increased significantly, and the connectivity between mesopores and macropore-microfractures was enhanced, which was characterized by the increase in effective porosity and nuclear magnetic permeability of coal samples. After acidification, the pore-throat ratio of adsorption pores of all coal samples decreased, while the pore-throat ratio of seepage pores increased. By comparatively analyzing the change law of pore structure of coal samples before and after acidizing with three kinds of mixed acid fluids, the optimal mixed acid fluid suitable for acidizing and permeability improvement of high rank coal in the Jiaozuo coal mine area was selected, which was 12%HCL +3%HF.

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“…By analyzing the T 2 spectra of saturated and centrifuged samples, one can obtain information about the porosity, permeability, pore size distribution, and fluid saturation. 13 , 22 − 25 For example, Lucas-Oliveira et al 26 compared experimental and simulated NMR data with gas permeability through the combination of experiments and simulations and proved that the pore size distribution could be obtained using the T 2 relaxation spectrum. Zheng 20 and Liang et al 27 obtained accurate pore size distributions from NMR T 2 distributions by combining NMR and centrifugation experiments.…”

Section: Introductionmentioning

confidence: 99%

“…The low-field nuclear magnetic resonance (NMR) method has been increasingly widely used in the evaluation of the pore structure of coal because of its high speed, nondestructive nature, large sample size, wide measurement range, etc. , By measuring the relaxation characteristics of the 1 H fluid (water) in pores by low-field NMR, the pore structure and flow characteristics of coal samples can be obtained. By analyzing the T 2 spectra of saturated and centrifuged samples, one can obtain information about the porosity, permeability, pore size distribution, and fluid saturation. ,− For example, Lucas-Oliveira et al compared experimental and simulated NMR data with gas permeability through the combination of experiments and simulations and proved that the pore size distribution could be obtained using the T 2 relaxation spectrum. Zheng and Liang et al obtained accurate pore size distributions from NMR T 2 distributions by combining NMR and centrifugation experiments.…”

Section: Introductionmentioning

confidence: 99%

Study on the Quantitative Characterization and Seepage Evolution Characteristics of Pores of Loaded Coal Based on NMR

et al. 2021

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Quantitative characterization of the pore structure and gas seepage characteristics of loaded coal is of great significance to the study of high-efficiency gas drainage in coal seams. Aiming at the problem of imperfect characterizations of coal seepage characteristics based on nuclear magnetic resonance (NMR), a calculation method for the pore permeability of coal with different pore diameters is proposed. The pore structure and seepage characteristics of coal have been quantitatively studied using a nuclear magnetic resonance (NMR) system. The results show that with increasing external load, the proportion of the pore volume of the coal sample in the range of 0.01−0.52 μm gradually decreases, while that in the range of 5.11−352.97 μm increases. In this process, the porosity increases from 0.9967 to 1.0103%, the connectivity increases from 0.1718 to 0.2391, and the permeability increases from 2.64 × 10 −6 to 8.20 × 10 −6 μm 2 . The calculation of the coal sample connectivity and permeability using the improved NMR permeability component proves that 94.37−352.97 μm pores are the main channel of fluid flow. When the axial pressure increases, the coal body permeability in the aperture range of 94.37−352.97 μm rapidly increases. The improved permeability component calculation model can better reflect the variation law of pore permeability of the loaded coal body.

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Nuclear magnetic resonance study of the influence of the liquid nitrogen freeze‐thaw process on the pore structure of anthracite coal

Cited by 40 publications

References 41 publications

Prediction of methane adsorption capacity in different rank coal at low temperature by the Polanyi‐based isotherm model

Prediction of methane adsorption capacity in different rank coal at low temperature by the Polanyi‐based isotherm model

Effect of Mixed Acid Fluid on the Pore Structure of High Rank Coal and Acid Fluid Optimization

Study on the Quantitative Characterization and Seepage Evolution Characteristics of Pores of Loaded Coal Based on NMR

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