Influence mechanism of gas pressure reduction on coal deformation and seepage

doi:10.16265/j.cnki.issn1003-3033.2022.04.019

Abstract

Abstract:

In order to study coal deformation and gas seepage behaviors caused by pressure reduction in gas extraction process, based on seepage test and triaxial compression test of gas pressure reduction, coal deformation and seepage characteristics were obtained. Then, matrix shrinkage deformation was modified by considering adsorption damage, and a permeability model was constructed before its rationality was verified by experimental results. The results show that with the decrease of gas pressure, coal permeability presents a "V" shaped change trend. The axial and radial deformation increase linearly, and coals injected with CO₂ produce larger deformation than that with CH₄, with radial deformation being 1.89 times of axial deformation. Moreover, the elastic modulus and peak principal stress difference in coal with CO₂ are lower to different extent than those with CH₄. In order to ensure safe production, attention should be paid to the issue of coal strength reduction caused by CO₂ injection into coal seam when using CO₂ displacement or CO₂ fracturing anti-reflection technology.

Key words: gas extraction, gas pressure reduction, coal deformation, matrix shrinkage, adsorption damage, seepage test

WU Xuehai, LI Bobo, GAO Zheng, XU Jiang, FU Jiale. Influence mechanism of gas pressure reduction on coal deformation and seepage[J]. China Safety Science Journal, 2022, 32(4): 129-134.

Figures/Tables 7

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References 15

[1]	HOU Xiaowei, LIU Shimin, LI Guofu, et al. Quantifying and modeling of in situ stress evolutions of coal reservoirs for helium, methane, nitrogen and CO₂ depletions[J]. Rock Mechanics and Rock Engineering, 2021, 54: 3701-3719. doi: 10.1007/s00603-021-02511-1
[2]	陈结, 潘孝康, 姜德义, 等. 三轴应力下软煤和硬煤对不同气体的吸附变形特性[J]. 煤炭学报, 2018, 43(增1): 149-157.
	CHEN Jie, PAN Xiaokang, JIANG Deyi, et al. Adsorption deformation characteristics of soft coal and hard coal to different gases under triaxial stress condition[J]. Journal of China Coal Society, 2018, 43(S1): 149-157.
[3]	黎力, 梁卫国, 李治刚, 等. 注热CO₂驱替增产煤层气试验研究[J]. 煤炭学报, 2017, 42(8): 2044-2051.
	LI Li, LIANG Weiguo, LI Zhigang, et al. Experimental investigation on enhancing coalbed methane recovery by injecting high temperature CO₂[J]. Journal of China Coal Society, 2017, 42(8): 2044-2051.
[4]	张庆贺, 杨科, 袁亮, 等. 吸附性气体对构造煤的损伤效应试验研究[J]. 采矿与安全工程学报, 2019, 36(5): 995-1001.
	ZHANG Qinghe, YANG Ke, YUAN Liang, et al. Experimental study on damage effect of adsorbed gas on structural coal[J]. Journal of Mining & Safety Engineering, 2019, 36(5): 995-1001.
[5]	LIU Ting, LIU Shimin, LIN Baiquan, et al. Stress response during in-situ gas depletion and its impact on permeability and stability of CBM reservoir[J]. Fuel, 2020, 266: DOI: 10.1016/j.fuel.2020.117083. doi: 10.1016/j.fuel.2020.117083
[6]	ZHENG Chunshan, KIZIL M S, CHENG Zhongwei, et al. Role of multi-seam interaction on gas drainage engineering design for mining safety and environmental benefits: linking coal damage to permeability variation[J]. Process Safety and Environmental Protection, 2018, 114: 310-322. doi: 10.1016/j.psep.2018.01.011
[7]	袁欣鹏, 梁冰, 孙维吉, 等. 卸压煤层瓦斯抽采渗透率演化模型研究[J]. 中国安全科学学报, 2016, 26(2): 127-131.
	YUAN Xinpeng, LIANG Bing, SUN Weiji, et al. Research on permeability evolution model for coal seam being drained by pressure relief[J]. China Safety Science Journal, 2016, 26(2): 127-131.
[8]	WANG Gongda, REN Ting, WANG Kai, et al. Improved apparent permeability models of gas flow in coal with Klinkenberg effect[J]. Fuel, 2014, 128: 53-61. doi: 10.1016/j.fuel.2014.02.066
[9]	张遵国, 曹树刚, 洪林, 等. 突出危险型煤瓦斯等温解吸试验研究[J]. 中国安全科学学报, 2017, 27(7): 115-120. doi: 10.16265/j.cnki.issn1003-3033.2017.07.021
	ZHANG Zunguo, CAO Shugang, HONG Lin, et al. Experimental study on isothermal desorption of methane from outburst-prone briquette[J]. China Safety Science Journal, 2017, 27(7): 115-120. doi: 10.16265/j.cnki.issn1003-3033.2017.07.021
[10]	LI Bobo, REN Chonghong, WANG Zhihe, et al. Experimental study on damage and the permeability evolution process of methane-containing coal under different temperature conditions[J]. Journal of Petroleum Science and Engineering, 2020, 184: DOI: 10.1016/j.petrol.2019.106509. doi: 10.1016/j.petrol.2019.106509
[11]	李波波, 吴学海, 任崇鸿, 等. 瓦斯气体劣化—荷载作用下煤岩损伤本构模型[J]. 中国安全科学学报, 2021, 31(7): 76-81. doi: 10.16265/j.cnki.issn 1003-3033.2021.07.011
	LI Bobo, WU Xuehai, REN Chonghong, et al. Constitutive model of coal damage under gas degradation and load[J]. China Safety Science Journal, 2021, 31(7): 76-81. doi: 10.16265/j.cnki.issn 1003-3033.2021.07.011
[12]	GUO Haijun, CHENG Yuanping, REN Ting, et al. Pulverization characteristics of coal from a strong outburst-prone coal seam and their impact on gas desorption and diffusion properties[J]. Journal of Natural Gas Science and Engineering, 2016, 33: 867-878. doi: 10.1016/j.jngse.2016.06.033
[13]	XIE Jing, GAO Mingzhong, YU Bin, et al. Coal permeability model on the effect of gas extraction within effective influence zone[J]. Geomechanics and Geophysics for Geo-Energy and Geo-Resources, 2015, 1: 15-27. doi: 10.1007/s40948-015-0002-2
[14]	李波波, 高政, 杨康, 等. 温度与孔隙压力耦合作用下煤岩吸附-渗透率模型研究[J]. 岩石力学与工程学报, 2020, 39(4): 24-37.
	LI Bobo, GAO Zheng, YANG Kang, et al. Study on coal adsorption-permeability model under the coupling of temperature and pore pressure[J]. Chinese Journal of Rock Mechanics and Engineering, 2020, 39(4): 24-37.
[15]	XUE Yi, RANJITH P G, GAO Feng, et al. Mechanical behaviour and permeability evolution of gas-containing coal from unloading confining pressure tests[J]. Journal of Natural Gas Science and Engineering, 2017, 40: 336-346. doi: 10.1016/j.jngse.2017.02.030

气体类型	弹性模量 E/MPa	峰值主应力差 Δσ_c/MPa	泊松比 ν
CH₄	853.13	25.80	0.24
CO₂	816.41	23.33	0.24

参数	气体类型
参数	CH₄	CO₂
B	0.876	1.000
k_a/10^-3μm²	0.038	0.036
ε_L	0.084	0.068
p_L/MPa	4.176	4.956
ζ	0.219	0.670