Experimental study on gas diffusion dynamics in fractured coal: A better understanding of gas migration in in-situ coal seam

Liu, Ting; Lin, Baiquan; Fu, Xuehai; Gao, Yabin; Kong, Jie; Zhao, Yang; Song, Haoran

doi:10.1016/j.energy.2020.117005

Cited by 115 publications

(50 citation statements)

References 34 publications

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“…Diffusion coefficient is an important parameter of reaction gas diffusion ability, which is related to coal structure, metamorphic degree, particle size, and other factors [29][30][31][32]. The gas diffusion ability also has a significant effect on the gas expansion energy, as shown in Figure 6.…”

Section: Influencing Factors Of Gas Expansion Energymentioning

confidence: 99%

Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Cao¹,

Hu²,

Yong-liang³

et al. 2021

Geofluids

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Due to the insufficient understanding of the outburst mechanism, the coal and gas outburst disasters in China are more serious. Gas expansion energy is the main source of energy that causes outburst. In order to explore the distribution law of gas expansion energy in outburst coal seams, a gas-solid coupling equation of outburst coal seams was established. The distribution law of coal stress field, deformation field, gas flow field, and gas expansion energy were simulated and analyzed by using COMSOL Multiphysics. The results showed that from the excavation face to the deep part of coal seam, the stress presented unloading zone, stress concentration zone, and original stress zone. The volumetric strain and permeability reached the minimum, while the gas pressure reached the maximum at the peak value of vertical stress. As time goes on, the gas pressure in the fracture near the working face gradually decreased and was less than the pressure in coal matrix. The total gas expansion energy consists of free gas and desorption gas expansion energy. Affected by the excavation, free gas expansion energy maintained a constant value in the original coal seam and gradually decreased in the area close to the working face. The expansion energy provided by desorption gas was zero in the original coal seam. And it first increased and then decreased rapidly near the working face. Compared with stress and coal seam thickness, gas pressure and initial diffusion coefficient had significant influence on gas expansion energy of coal seam. When the diffusion coefficient was greater than 1e-9 m2/s, the gas expansion energy of the coal seam near the working face was significantly higher than that of the original coal seam, which had the risk of inducing outburst.

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Section: Influencing Factors Of Gas Expansion Energymentioning

confidence: 99%

Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Cao¹,

Hu²,

Yong-liang³

et al. 2021

Geofluids

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“…where t is the time, s; p f g is the pressure of coal seam gas in the fracture, MPa; and τ is the desorption time of coal seam gas, reflecting the emission capacity of coal matrix, which is equal to the time taken for the matrix to desorb 63.2% of coal seam gas. By introducing equations (1) and (2) into equation 4, the transport equation of coal seam gas in coal matrix can be obtained [13]:…”

Section: Controlling Mathematic Equationsmentioning

confidence: 99%

“…Gas drainage can reduce the gas content and gas pressure within coal seams, which is an effective way to eliminate outburst disaster [6][7][8]. Many measures were applied to increase the preextraction efficiency in the soft coal seam, including hydraulic fracturing, hydraulic punching, and presplitting blasting, methane driven by gas injection [9][10][11][12][13][14]. However the effect is limited.…”

Section: Introductionmentioning

confidence: 99%

Investigation of Large-Diameter Borehole for Enhancing Permeability and Gas Extraction in Soft Coal Seam

Wang¹,

Yan

Ren

et al. 2020

Geofluids

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The efficiency of gas extraction from the soft coal seam with ultralow permeability is low. Gas extraction with large-diameter borehole is proposed to deplete gas content for preventing gas outburst disaster in this study. The fractures around the large borehole will enhance the permeability in the damage area to promote gas extraction. We established a damage-stress-seepage coupling model for large-diameter borehole gas extraction in soft coal seam. This mathematical model contains governing equations of gases sorption and transport, coal deformation, and damage, reflecting the coupling responses between gas and coal seam. The model is solved by the finite element method to simulate the gas drainage large-diameter borehole through roadway. Distributions of elastic modulus, damage area, and maximum principal stress in soft coal seam with different borehole diameters including 94 mm, 133 mm, 200 mm, and 300 mm are analyzed. The gas pressure, gas content, and effective extraction area in soft coal seam are discussed. Results show that the shear failure zone appears around the large-diameter borehole, and its permeability rises sharply. This opens up the gas transport channel and is conducive to the rapid extraction. It is confirmed that gas extraction using large-diameter borehole (300 mm) can greatly improve the efficiency of the gas preextraction in soft coal seam by increasing gas extraction rate. These provide a foundation for guiding the operation of gas extraction with large borehole from the soft coal seam in the field.

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“…The coal body was partially damaged by the pressure, causing fracturing in the hole and enhancing the permeability of the coal and associated rocks 33‐37 . When the LCO 2 was heated and pressurized via subjection to a phase change, the seepage and diffusion rates of the CO 2 in the coal pores increased, thereby enhancing free gas displacement 38‐41 . Thus, the CO 2 competes with the adsorbed CH 4 on the coal surface for displacement, and this can effectively improve CH 4 extraction efficiency 42 .…”

Section: Engineering Design and Implementation Of The Lco2 Coal Fractmentioning

confidence: 99%

“…[33][34][35][36][37] When the LCO 2 was heated and pressurized via subjection to a phase change, the seepage and diffusion rates of the CO 2 in the coal pores increased, thereby enhancing free gas displacement. [38][39][40][41] Thus, the CO 2 competes with the adsorbed CH 4 on the coal surface for displacement, and this can effectively improve CH 4 extraction efficiency. 42 In fact, the LCO 2 injection into the coal seam involves the dual gas drainage effect, which improves the permeability of the seam through fracturing and CH 4 displacement, thereby achieving stimulation and reformation of the coal seam.…”

Section: Principle Of Lco 2 Coal Fracturing and Gas Extractionmentioning

confidence: 99%

Liquid CO ₂ high‐pressure fracturing of coal seams and gas extraction engineering tests using crossing holes: A case study of Panji Coal Mine No. 3, Huainan, China

et al. 2020

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Summary Owing to the low coal permeability coefficients and poor gas extraction efficiencies associated with the extraction of coal in the Huainan coal mining area, the aim of this study was to design, for the first time, a high‐pressure low‐temperature liquid CO2 (LCO2) pump for engineering tests with respect to the fracturing of coal seams and the improvement of CH4 recovery in China. To reasonably calculate the initiation pressure for the coal seam fracturing as well as the gas flow parameters, theoretical analysis with field testing were integrated in the design. In addition, considering the interim gas extraction standard, the gas extraction equivalent radius based on this standard was calculated. The test results revealed a maximum LCO2 pressure of 20.6 MPa, which surpasses the theoretical maximum pressure (19.5 MPa) required for the fracturing of coal seams. During the entire gas extraction process, the CO2 concentrations in boreholes K1 and K3 decrease exponentially with time, showing attenuation coefficients of 0.0205 and 0.0231, respectively. The attenuation coefficients of the three attenuation stages of the original coal seam gas flow rate were 0.0314, 0.2142, and 0.1198, which were higher than those corresponding to the test area. The CH4 concentration in boreholes K1 and K3 in the test area were both higher than that in the original coal seam, and the maximum CH4 flow rates in these boreholes were 1.31‐ and 1.72‐fold higher than that in the original coal seam, respectively. The comparative analysis of CH4 concentrations and flow rates indirectly showed an improvement in the permeability of the coal seam. Further, a quantitative equivalent gas extraction evaluation method based on LCO2 fracturing of coal seam and gas displacement was proposed. Furthermore, based on a comprehensive evaluation, the effective displacement radius caused by the LCO2 fracturing test was 9 m, with a displacement efficiency of 23.95%, and a displacement volume ratio of 0.21. This method offered the possibility of realizing the quantitative evaluation of the LCO2 injection amount and the gas extraction effect, and provides a basis for optimizing the LCO2 fracturing of coal seams as well as the gas extraction process.

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Experimental study on gas diffusion dynamics in fractured coal: A better understanding of gas migration in in-situ coal seam

Cited by 115 publications

References 34 publications

Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Investigation of Large-Diameter Borehole for Enhancing Permeability and Gas Extraction in Soft Coal Seam

Liquid CO ₂ high‐pressure fracturing of coal seams and gas extraction engineering tests using crossing holes: A case study of Panji Coal Mine No. 3, Huainan, China

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Experimental study on gas diffusion dynamics in fractured coal: A better understanding of gas migration in in-situ coal seam

Cited by 115 publications

References 34 publications

Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Gas Expansion Energy Model and Numerical Simulation of Outburst Coal Seam under Multifield Coupling

Investigation of Large-Diameter Borehole for Enhancing Permeability and Gas Extraction in Soft Coal Seam

Liquid CO 2 high‐pressure fracturing of coal seams and gas extraction engineering tests using crossing holes: A case study of Panji Coal Mine No. 3, Huainan, China

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Product

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Liquid CO ₂ high‐pressure fracturing of coal seams and gas extraction engineering tests using crossing holes: A case study of Panji Coal Mine No. 3, Huainan, China