Characteristics of coalbed gas seepage under asymmetric loading and optimization of extraction radius

doi:10.16265/j.cnki.issn1003-3033.2024.12.0905

Abstract

Abstract:

To reveal the influence of asymmetric load on gas seepage and extraction radius, a multi-physics coal and gas fluid-solid coupling model was proposed to analyze the gas seepage characteristics of coal seams. Matrix-adsorbed gas was used as the mass source in the proposed model introducing asymmetric loads into the boundary conditions. Furthermore, segmented drilling was used under asymmetric load conditions to optimize the gas extraction radius and improve extraction efficiency. The results indicated that greater stress compressed the cracks inside the concentrated stress zone, making it more difficult for gas to flow and to be extracted more challenging. The gas pressure in the concentrated stress zone decreased by approximately 2% less than that in the original stress zone, and the permeability decreased by about 9%. Asymmetric load had different degrees of influence on the diffusion and seepage processes. Within 180 days, the mass of diffused gas of the original stress area decreased by 19% and the seepage mass decreased by 20.5%, while these values in the concentrated stress zone decreased by 16.9% and 17.9%, respectively. Asymmetric loads had adverse effects on gas extraction, increasing extraction time under uniform load conditions. By adjusting the extraction radius under asymmetric load conditions, not only can the extraction efficiency be improved by approximately 3%, but it can also ensure that the extraction standards are met within 180 days, thereby effectively improving the overall performance of gas extraction.

Key words: asymmetric load, coal seam gas, gas seepage, extraction radius, gas drainage, permeability

CLC Number:

X936

YAN Lu, WANG Tao, WANG Liancong, LI Wenpu, ZHAO Tianwei. Characteristics of coalbed gas seepage under asymmetric loading and optimization of extraction radius[J]. China Safety Science Journal, 2024, 34(12): 149-158.

Figures/Tables 12

Fig.1

Fig.2

Table 1

Parameters for numerical simulation

参数	数值	参数	数值
$ϕ m 0$	0.012	$ρ c$ / (kg·m^-3)	1 450
$ϕ f 0$	0.06	抽采负压/ kPa	87
$k 0$ /mD	0.01	吸附时间/ d	12
Mc/(kg·mol^-1)	0.016	钻孔半径/ m	0.1
R/(J·mol^-1·K^-1)	8.413 5	煤的泊松比	0.339
煤层温度/K	293	极限吸附变形量	0.004
甲烷动力黏度/ (Pa·s)	1.08 $× 1$ 0^-5	K/ MPa	2 713
$P m$ /MPa	1	$K m$ / MPa	8 139
$P L$ /MPa	1	$F x$ / MPa	7
$V L$ /(m³·kg^-1)	0.02	$F y$ / MPa	12
标况甲烷摩尔质量/(m³ ·mol^-1)	0.022 4	$F z$ / MPa	5

Table 1

Fig.3

Fig.4

Fig.5

Fig.6

Fig.7

Fig.8

Fig.9

Table 2

Fig.10

References 24

[1]	周世宁, 孙辑正. 煤层瓦斯流动理论及其应用[J]. 煤炭学报, 1965, 1(1): 24-37.
	ZHOU Shining, SUN Jizheng. Theory of coal seam gas flow and its applications[J]. Journal of China Coal Society, 1965, 1(1): 24-37.
[2]	郭勇义, 周世宁. 煤层瓦斯一维流场流动规律的完全解[J]. 中国矿业学院学报, 1984, 2(2): 22-31.
	GUO Yongyi, ZHOU Shining. Complete solution of one-dimensional flow field rules in coal seam gas[J]. Journal of China University of Mining and Technology, 1984, 2(2): 22-31.
[3]	汪有刚, 李宏艳, 齐庆新, 等. 采动煤层渗透率演化与卸压瓦斯抽放技术[J]. 煤炭学报, 2010, 35(3): 406-410.
	WANG Yougang, LI Hongyan, QI Qingxin, et al. Permeability evolution of mining coal seam and pressure relief gas extraction technology[J]. Journal of China Coal Society, 2010, 35(3): 406-410.
[4]	杨天鸿, 陈仕阔, 朱万成, 等. 煤层瓦斯卸压抽放动态过程的气-固耦合模型研究[J]. 岩土力学, 2010, 31(7): 2247-2252.
	YANG Tianhong, CHEN Shikuo, ZHU Wancheng, et al. Study on gas-solid coupling model for dynamic process of gas relief and drainage in coal seam[J]. Rock and Soil Mechanics, 2010, 31(7): 2247-2252.
[5]	卢平, 袁亮, 程桦, 等. 低透气性煤层群高瓦斯采煤工作面强化抽采卸压瓦斯机理及试验[J]. 煤炭学报, 2010, 35(4): 580-585.
	LU Ping, YUAN Liang, CHENG Hua, et al. Mechanism and experiment of enhanced extraction of pressure relief gas from high gas mining face in low permeability coal seam group[J]. Journal of China Coal Society, 2010, 35(4): 580-585.
[6]	梁冰, 章梦涛, 王泳嘉. 煤层瓦斯渗流与煤体变形的耦合数学模型及数值解法[J]. 岩石力学与工程学报, 1996, 15(2): 40-47.
	LIANG Bing, ZHANG Mengtao, WANG Yongjia. Coupling mathematical model and numerical solution of gas seepage and coal deformation in coal seam[J]. Chinese Journal of Rock Mechanics and Engineering, 1996, 15(2): 40-47.
[7]	尹光志, 王登科, 张东明, 等. 含瓦斯煤岩固气耦合动态模型与数值模拟研究[J]. 岩土工程学报, 2008, 30(10): 1430-1436.
	YIN Guangzhi, WANG Dengke, ZHANG Dongming, et al. Study on dynamic model and numerical simulation of gas-bearing coal[J]. Chinese Journal of Geotechnical Engineering, 2008, 30(10): 1430-1436.
[8]	张浩浩, 李胜, 范超军, 等. 煤岩渗透率各向异性模型及瓦斯抽采模拟研究[J]. 中国安全科学学报, 2018, 28(12):109-115. doi: 10.16265/j.cnki.issn1003-3033.2018.12.018
	ZHANG Haohao, LI Sheng, FAN Chaojun, et al. Research on anisotropy model of coal permeability and gas extraction simulation[J]. China Safety Science Journal, 2018, 28(12):109-115. doi: 10.16265/j.cnki.issn1003-3033.2018.12.018
[9]	郝天轩, 宋超. 数值模拟结合SF6示踪法确定煤层钻孔瓦斯抽采有效半径[J]. 中国安全科学学报, 2013, 23(1):22-27.
	HAO Tianxuan, SONG Chao. Numerical simulation and SF6 tracer method to determine the effective radius of gas extraction in coal seam borehole[J]. China Safety Science Journal, 2013, 23(1):22-27.
[10]	周红星, 程远平, 谢战良. 计算机模拟确定瓦斯抽放有效半径的方法研究[J]. 能源技术与管理, 2005, 4(4): 81-82.
	ZHOU Hongxing, CHENG Yuanping, XIE Zhanliang. Study on the method of determining effective radius of gas drainage by computer simulation[J]. Energy Technology and Management, 2005, 4(4): 81-82.
[11]	齐黎明, 祁明, 陈学习. 抽采钻孔周围煤层瓦斯压力分布理论分析及应用[J]. 中国安全科学学报, 2018, 28(7):102-108. doi: 10.16265/j.cnki.issn1003-3033.2018.07.017
	QI Liming, QI Ming, CHEN Xuexi. Theoretical analysis and application of gas pressure distribution in coal seam around extraction borehole[J]. China Safety Science Journal, 2018, 28(7):102-108. doi: 10.16265/j.cnki.issn1003-3033.2018.07.017
[12]	马耕, 苏现波, 魏庆喜. 基于瓦斯流态的抽放半径确定方法[J]. 煤炭学报, 2009, 34(4): 501-504.
	MA Geng, SU Xianbo, WEI Qingxi. Extraction radius determination method based on gas flow pattern[J]. Journal of China Coal Society, 2009, 34(4): 501-504.
[13]	张明杰, 贾文超, 梁锡明, 等. 基于瓦斯自然涌出规律的有效抽采半径研究[J]. 中国安全科学学报, 2018, 28(10):98-104. doi: 10.16265/j.cnki.issn1003-3033.2018.10.017
	ZHANG Mingjie, JIA Wenchao, LIANG Ximing, et al. Research on effective extraction radius based on natural gas emission law[J]. China Safety Science Journal, 2018, 28(10):98-104. doi: 10.16265/j.cnki.issn1003-3033.2018.10.017
[14]	李润芝, 梁冰, 孙维吉, 等. 顺层钻孔瓦斯抽采半径及布孔间距试验研究[J]. 中国安全科学学报, 2016, 26(10):133-138.
	LI Ruizhi, LIANG Bing, SUN Weiji, et al. Experimental study on gas extraction radius and spacing of borehole in bedding borehole[J]. China Safety Science Journal, 2016, 26(10):133-138.
[15]	郝富昌, 刘彦伟, 龙威成, 等. 蠕变-渗流耦合作用下不同埋深有效抽采半径研究[J]. 煤炭学报, 2017, 42(10): 2616-2622.
	HAO Fuchang, LIU Yanwei, LONG Weicheng, et al. Study on effective extraction radius at different buried depths under creep and seepage coupling[J]. Journal of China Coal Society, 2017, 42(10): 2616-2622.
[16]	张钧祥, 李波, 韦纯福, 等. 基于扩散-渗流机理瓦斯抽采三维模拟研究[J]. 地下空间与工程学报, 2018, 14(1): 109-116.
	ZHANG Junxiang, LI Bo, WEI Chunfu, et al. Three-dimensional simulation of gas extraction based on diffusion-seepage mechanism[J]. Chinese Journal of Underground Space and Engineering, 2018, 14(1): 109-116.
[17]	吴世跃. 煤层气与煤层耦合运动理论及其应用的研究[D]. 沈阳: 东北大学, 2006.
	WU Shiyue. Research on the theory and application of coalbed methane and coal seamcoupling movement[D]. Shenyang: Northeastern University, 2006.
[18]	AN Fenghua, CHENG Yuanping, WANG Liang, et al. A numerical model for outburst including the effect of adsorbed gas on coal deformation and mechanical properties[J]. Computers and Geotechnics, 2013, 54: 222-231.
[19]	梁冰, 章梦涛, 潘一山, 等. 瓦斯对煤的力学性质及力学响应影响的试验研究[J]. 岩土工程学报, 1995, 17(5): 12-18.
	LIANG Bing, ZHANG Mengtao, PAN Yishan, et al. Experimental study on the effect of gas on mechanical properties and mechanical response of coal[J]. Chinese Journal of Geotechnical Engineering, 1995, 17(5): 12-18.
[20]	陈勉, 陈至达. 多重孔隙介质的有效应力定律[J]. 应用数学和力学, 1999, 20(11): 1121-1127.
	CHEN Mian, CHEN Zhida, The effective stress law of porous media with multiple pores[J]. Applied Mathematics and Mechanics, 1999, 20(11): 1121-1127.
[21]	ZHANG Hongbin, LIU Jishan, ELSWORTH D, et al. How sorption-induced matrix deformation affects gas flow in coal seams: a new FE model[J]. International Journal of Rock Mechanics and MiningSciences, 2008, 45(8):1226-1236.
[22]	WU Yu, LIU Jishan, ELSWORTH D, et al. Dual poroelastic response of a coal seam to CO₂ injection[J]. International Journal of Greenhouse Gas Control, 2010, 4: 668-678.
[23]	曹新奇, 辛海会, 徐立华, 等. 瓦斯抽放钻孔有效抽放半径的测定[J]. 煤炭工程, 2009, 41(9): 88-90.
	CAO Xinqi, XIN Haihui, XU Lihua, et al. Determination of effective drainage radius of gas drainage borehole[J]. Coal Engineering, 2009, 41(9): 88-90.
[24]	梁冰, 袁欣鹏, 孙维吉, 等. 分组测压确定瓦斯有效抽采半径试验研究[J]. 采矿与安全工程学报, 2013, 30(1): 132-135.
	LIANG Bing, YUAN Xinpeng, SUN Weiji, et al. Experimental study on determining effective gas extraction radius by group pressure measurement[J]. Journal of Mining and Safety Engineering, 2013, 30(1): 132-135.

类别	原始瓦斯量/ (kg·m^-3)	总瓦斯含量/ (kg·m^-3)	瓦斯扩散量/ (kg·m^-3)	瓦斯渗流量/ (kg·m^-3)	抽采率/ %
无优化	1 501.6	1 041.8	34.014	6.63	30.62
优化后	1 501.6	994.8	31.66 8	6.150 6	33.75