Investigations on the mechanism of the microstructural evolution of different coal ranks under liquid nitrogen cold soaking
Investigations on the mechanism of the microstructural evolution of different coal ranks under liquid nitrogen cold soaking
复制标题
液氮冷浸不同煤阶微观结构演化机制研究
DOI：
10.1080/15567036.2020.1841856
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发表时间：
2020-11-01
影响因子：
2.9
通讯作者：
Zhang, Dongming
中科院分区：
文献类型：
--
作者：
Liu, Shumin;Li, Xuelong;Zhang, Dongming
液氮是改善煤储层渗透率的重要手段。液氮浸泡法具有广泛的应用前景。然而，还没有足够的研究来突出使用液氮增加不同煤样品的渗透率的效果。因此，本研究进行了研究冷浸泡在液氮中使用不同的煤阶，如肥煤，瘦煤和无烟煤，其孔结构和分形特征的影响。利用FHH分形理论研究了不同煤种在液氮中浸泡前后孔隙的分形维数特征。此外，还研究了分形维数与孔隙参数之间的关系。结果表明，肥煤、瘦煤和无烟煤在液氮中冷浸前后的低温氮吸附曲线均为“S”型。煤的总孔容和孔表面积在液氮冷浸后增加。液氮冷浸能有效地改变不同煤种的内部孔隙结构。此外，煤的孔隙结构的非均匀性增强后，液氮冷浸泡沿着的分形维数增加。随着变质程度的增加，生长速度也随之降低。煤在液氮冷浸过程中发生不均匀收缩，产生的热应力大于煤的抗拉强度，促进了煤的多孔结构的发育。这些结果有利于揭示煤层在液氮裂解过程中宏观和微观孔隙裂隙空间扩展和连通规律。
Liquid nitrogen (LN2) is an important means to improve the permeability of coal reservoirs. The LN2 soaking method has a wide range of application prospects. However, not enough studies exist to highlight the effect of increasing the permeability of different coal samples using LN2. Hence, this investigation was carried out to examine the effect of cold soaking in LN2 using different coal ranks such as fat coal, lean coal and anthracite coal, on their pore structures and fractal characteristics. Frenkel-Halsey-Hill (FHH) fractal theory was used to understand the fractal dimension characteristics of pores in these different coals before and after cold soaking in LN2. Furthermore, the relationship between the fractal dimensions and pore parameters was also studied. The results show that low-temperature nitrogen adsorption curves of fat coal, lean coal and anthracite before and after cold soaking in LN2 are "S" type. An increase in the total pore volume and pore surface area of coal after LN2 cold soaking is noted. LN2 cold soaking is found to transform the internal pore structure of different coals effectively. Moreover, the heterogeneity of the porous structure of coal is enhanced after LN2 cold soaking along with an increase in the fractal dimension. The growth also decreases with an increase in the metamorphism. The uneven shrinkage of coal occurred during LN2 cold soaking, and the thermal stress generated is greater than the tensile strength of coal, which promotes the development of the porous structure of coal. These results are beneficial in revealing the macroscopic and microscopic pore fissure space expansion and connectivity law of coal seam during the process of LN2 cracking.