煤孔隙结构对瓦斯解吸−扩散−渗流过程的影响

贾男

doi:10.13272/j.issn.1671-251x.2023110076

煤孔隙结构对瓦斯解吸−扩散−渗流过程的影响

doi: 10.13272/j.issn.1671-251x.2023110076

贾男^{1, 2,}

1.
中煤科工集团沈阳研究院有限公司，辽宁抚顺　113122
2.
煤矿安全技术国家重点实验室，辽宁抚顺　113122

基金项目: 辽宁省科技计划联合基金项目（2023JH2/101700008）。

详细信息

作者简介:
贾男（1989—），男，锡伯族，辽宁沈阳人，副研究员，硕士，主要研究方向为煤矿瓦斯治理，E-mail：jn_1989@163.com

中图分类号: TD712
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出版历程
- 收稿日期: 2023-11-23
- 修回日期: 2024-03-18
- 网络出版日期: 2024-04-11

The influence of coal pore structure on gas desorption-diffusion-seepage process

JIA Nan^{1, 2
,}

1.
CCTEG Shengyang Research Insititute, Fushun 113122, China
2.
State Key Laboratory of Coal Mine Safety Technology, Fushun 113122, China

摘要

摘要: 充分认识煤层瓦斯运移机制是提升抽采效率的根本前提。而目前针对煤体瓦斯微观运移特性的研究探讨的多是煤微观孔隙瓦斯运移特性，忽略了瓦斯解吸−扩散过程。以焦煤为例，采用压汞测试、纳米级工业CT扫描和数值仿真，精准重构并定量表征了煤孔隙空间结构，从微观角度分析了瓦斯解吸−扩散−渗流的演化过程，初步探讨了煤孔隙空间结构对瓦斯运移的影响。结果表明：① 在孔隙中心位置的瓦斯压力相对较高，解吸−扩散由孔隙中心向边缘进行，不同时间及位置上瓦斯压力分布规律差异明显，造成瓦斯压力分布差异性的原因在于各代表性体积（REV）单元中孔隙与喉道的半径、长度、形状、连通性能不同。② 孔隙结构和拓扑优势拓展了瓦斯解吸−扩散−渗流范围，大尺寸孔隙结构能为气体分子提供多元化运动空间，削弱尺寸效应对扩散广度的影响，促进瓦斯解吸−扩散速率。③ 强非均质连通孔隙结构中，瓦斯渗流分散而高效，能通过广泛沟通煤基质完成气体由扩散到渗流的转变，提升瓦斯传质效率；弱非均质连通孔隙结构中，气体渗流路径单一、流线集中，渗流传质阻力较大，气体分子由扩散到渗流的转变效率低，不利于瓦斯高效运移。研究结果从微观角度丰富了煤体瓦斯运移理论，为瓦斯抽采工程实践提供了理论基础。
- 瓦斯抽采 /
- 煤层瓦斯 /
- 孔隙结构 /
- 瓦斯解吸 /
- 瓦斯扩散 /
- 瓦斯渗流 /
- CT扫描
Abstract: Fully understanding the mechanism of coal seam gas migration is the fundamental prerequisite for improving extraction efficiency. At present, research on the micro migration features of coal gas mostly focuses on the micro pore gas migration features of coal, ignoring the gas desorption-diffusion process. Taking coking coal as an example, the pore space structure of coal is accurately reconstructed and quantitatively characterized using mercury intrusion testing, nanoscale industrial CT scanning, and numerical simulation. The evolution process of gas desorption-diffusion-seepage is analyzed from a microscopic perspective, and the influence of coal pore space structure on gas migration is preliminarily explored. The results show the following points. ① The gas pressure is relatively high at the center of the pore, and desorption-diffusion proceeds from the center of the pore to the edge. The distribution of gas pressure varies significantly at different times and positions. The reason for the difference in gas pressure distribution is that the radius, length, shape, and connectivity of pores and throats in each representative elementary volume (REV) unit are different. ② The pore structure and topological advantages expand the range of gas desorption-diffusion-seepage. The large-sized pore structure can provide diversified movement space for gas molecules, weaken the influence of size effect on diffusion breadth, and promote the rate of gas desorption-diffusion. ③ In the strongly heterogeneous connected pore structure, gas seepage is dispersed and efficient, and the transformation of gas from diffusion to seepage can be achieved through extensive communication with the coal matrix, improving the efficiency of gas mass transfer. In weakly heterogeneous connected pore structures, the gas seepage path is single, the seepage lines are concentrated, the mass transfer resistance of the seepage is high, and the transformation efficiency of gas molecules from diffusion to seepage is low. It is not conducive to efficient gas migration. The research results enrich the theory of coal gas migration from a microscopic perspective and provide a theoretical basis for gas extraction engineering practice.
- gas extraction /
- coal seam gas /
- pore structure /
- gas desorption /
- gas diffusion /
- gas seepage /
- CT scan

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图 1 实验样品

Figure 1. Experimental samples

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图 2 实验仪器

Figure 2. Experimental instruments

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图 3 降噪前后CT图像对比

Figure 3. CT image comparison before and after noise reduction

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图 4 孔隙灰度阈值的Bi−PTI拟合结果

Figure 4. Bi-PTI fitting resules of pore gray threshold

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图 5 瓦斯边界条件

Figure 5. Gas boundary condition

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图 6 数字岩心重构结果

Figure 6. Digital core reconstruction results

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图 7 REV表征单元孔隙空间结构

Figure 7. Representative elementary volume(REV) characterisation of unit pore space structure

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图 8 孔隙等效直径分布规律

Figure 8. Distribution law of pore equivalent diameter

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图 9 孔隙体积分布规律

Figure 9. Distribution law of pore volume

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图 10 瓦斯压力空间分布

Figure 10. Space distribution of gas pressure

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图 11 REV单元y−z截面孔隙压力分布

Figure 11. Pore pressure distribution in y-z section of REV unit

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图 12 瓦斯渗流速度流线分布

Figure 12. Velocity streamline distribution of gas seepage

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表 1 Bi−PTI模型拟合参数

Table 1. Fitting parameters of Bi-PTI model

煤样	γ₁/ 10⁴ HU	γ₂/ 10⁴ HU	ζ₁/10⁻⁴	ζ₂/10⁻⁴	$\omega $	相关系数	G_m/HU
5号煤	5.32	3.81	3.110	0.94	0.44	0.99	10475
6号煤	1.31	2.45	2.100	0.81	0.65	0.99	12923

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表 2 数值模拟参数

Table 2. Numerical simulation parameters

参数	5号煤	6号煤
R/（J·K⁻¹·mol⁻¹）	8.314	8.314
T/K	303	303
s/m²	5.6×10⁻⁹	5.9×10⁻⁹
a/（m³·kg⁻¹）	0.0112	0.0112
b/MPa⁻¹	1.86×10⁻⁷	1.86×10⁻⁷
V_m/（m³·kg⁻¹）	0.024	0.024
f/m²	1×10⁻⁹	1.2×10⁻⁹
N_solid	2.2×10¹⁷	2.1×10¹⁷
V_voxel/m³	1×10⁻¹⁸	1×10⁻¹⁸
ρ/（kg·m⁻³）	1260	1260
V_e/m³	3.1×10⁻¹⁴	3.0×10⁻¹⁴
D/（m²·s⁻¹）	3.60×10⁻¹²	3.60×10⁻¹²
P/MPa	1.0×10⁻²	1.0×10⁻²

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