深部中阶煤孔结构的压汞—液氮联合表征及孔隙分形特征

Combined characterization of pore structure in deep medium-rank coal using mercury intrusion and liquid nitrogen adsorption methods and its pore fractal characteristics

李奇 吴勇 乔磊

LI Qi WU Yong QIAO Lei

1. 成都理工大学 环境与土木工程学院, 成都 610059; 2. 温州理工学院, 浙江 温州 325006; 3. 浙江省岩石力学与地质灾害重点实验室, 浙江 绍兴 312000

1. College of Environment and Civil Engineering, Chengdu University of Technology, Chengdu, Sichuan 610059, China; 2. Wenzhou University of Technology, Wenzhou, Zhejiang 325006, China; 3. Key Laboratory of Rock Mechanics and Geohazards of Zhejiang Province, Shaoxing, Zhejiang 312000, China

为研究深部中阶煤的孔隙结构特征与孔隙分形规律，利用压汞法和液氮吸附法对沈阳红阳三矿、开滦林西矿、淮南新集二矿和平顶山平煤六矿等典型深部开采矿区的主采煤层煤样进行了孔径、孔容、比表面积等参数测试，基于Menger海绵模型和FHH模型进行了孔隙分形规律的研究。结果表明：①基于压汞法的孔隙结构参数测试中平均孔径31.10~34.70 nm，总孔容0.048 3 ~0.059 4 mL/g，总比表面积5.590 9 ~7.652 8 m2/g，得出典型深部开采矿区的主采煤层孔隙发育比较接近；孔容分布以大孔孔容占主导，微孔与过渡孔孔容比重相当，中孔的孔容分布相对较小，表明大孔孔隙连通性较好，中孔较为闭塞；比表面积分布以微孔为主，占比达70%以上，而中孔和大孔的比重甚微，可见微孔吸附能力最强，不利于深部煤层瓦斯治理；Menger海绵模型分形维数介于2.6～3之间，表明孔隙形状很不规则，孔隙较为复杂，整体上孔隙表面较为粗糙。②基于液氮吸附法测试的有效孔径范围为3~177 nm，总孔容与比表面积不同的矿区差异明显，孔容分布以过渡孔和中孔为主，微孔分布较低，大孔为0，表明利用液氮吸附法对于中孔、过渡孔有很好的表征，而难以表征大孔结构，且微孔的孔隙连通性较差；比表面积分布中主要为过渡孔、微孔和中孔，大孔为0，其中以过渡孔为主，且其吸附能力也较强；FHH模型分形维数介于2.0~2.7，结构较为简单规则。③讨论了深部中阶煤孔隙结构差异性，其中压汞法和液氮法的孔隙结构参数(比表面积、孔容)随埋深的增加均呈非线性的凹曲线变化；Menger海绵模型与FHH模型分形维数则随埋深的增加呈凸曲线的变化趋势。

To study the pore structure and fractal characteristics of deep medium-rank coal, combined characterization using mercury intrusion and liquid nitrogen adsorption methods was conducted on coal samples from the main coal seams in typical deep mining areas, including Shenyang Hongyang Third Mine, Kailuan Linxi Mine, Huainan Xinji Second Mine, and Pingdingshan Pingmei Sixth Mine. Parameters such as pore size, pore volume, and specific surface area were obtained, and the pore fractal characteristics were studied based on the Menger sponge model and the FHH model. The results showed that: (1) Among the pore structure parameters tested with mercury intrusion method, the average pore size ranged from 31.10 to 34.70 nm, pore volume from 0.048 3 to 0.059 4 mL/g, and specific surface area from 5.590 9 to 7.652 8 m2/g. The pore development in the main coal seams of typical deep mining areas was relatively similar. The pore volume distribution was dominated by macropores, with micropores and transition pores contributing roughly equally, and mesopores having a relatively small distribution. This indicated that macropores had better connectivity and mesopores were more closed. Micropores accounted for more than 70% of the total specific surface area, while the proportions of mesopores and macropores were minimal, indicating that micropores had the strongest adsorption capacity, which was negatively affected gas management in deep coal seams. The fractal dimensions based on the Menger sponge model ranged from 2.6 to 3.0, indicating irregular pore shapes, complex pore structures, and generally rough pore surfaces. (2) The effective pore size tested using liquid nitrogen adsorption method ranged from 3 to 177 nm with significant differences in total pore volume and specific surface area among the mining areas. Pore volume distribution was dominated by transition pores and mesopores, with a lower distribution of micropores and no macropores. This indicated that liquid nitrogen adsorption was effective for characterizing mesopores and transition pores but struggled to characterize macropore structures. Moreover, the connectivity of micropores was relatively poor. The specific surface area was mainly composed of transition pores, micropores, and mesopores, with no macropores. Among them, transition pores were mostly dominant and had relatively strong adsorption capacity. The fractal dimensions based on the FHH model ranged from 2.0 to 2.7, indicating a relatively simple and regular structure. (3) The differences in pore structures of deep medium-rank coal were discussed. The pore structure parameters (specific surface area and pore volume) determined by mercury intrusion and liquid nitrogen adsorption methods showed a non-linear concave curve variation with increasing burial depth. The fractal dimensions derived from the Menger sponge model and the FHH model showed a convex curve trend with increasing burial depth.

浙江省岩石力学与地质灾害重点实验室开放基金项目(ZJRMG-2023-01)资助。

https://doi.org/10.11781/sysydz2025010130