基于 FE-SEM 的微生物降解煤岩孔隙演化特征
Evolution characteristics of coal pore structure by biodegradation based on FE-SEM
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摘要: 微生物降解煤岩作用具有增气、增孔、增解等优点已引起国内外学者广泛关注。 为探究微 生物降解过程中煤储层微观孔隙结构演化规律,利用场发射扫描电镜(FE-SEM)技术对鄂尔多斯 盆地南部黄陵矿区侏罗系原煤及微生物降解后煤的微观孔隙结构进行原位对比研究,发现了微生 物对煤岩微观孔隙改造的直接证据,基于图像二值化处理和盒维数分形方法定量表征了微生物降 解前后煤储层孔隙结构的分形维数变化规律。 结果表明:黄陵矿区原煤样品孔裂隙均比较发育,原 生孔以气孔为主,次生孔可见碎粒孔、角砾孔、摩擦孔等,裂隙以外生裂隙为主,宽度为 1 ~ 2 μm。 微生物降解后煤储层孔隙的形状和大小均发生改变,且孔隙直径变大。 煤有机质在微生物降解作 用下变得松散,并新增大量屑间孔。 在煤基质表面发现了微生物作用的痕迹,为微生物作用煤岩过 程提供了直接证据。 微生物降解后的煤孔隙结构分形维数降低,煤基质颗粒表面变得光滑,孔隙变 得简单,原始分形维数与其改变量呈正相关关系,表明煤储层的原始孔隙结构越复杂,微生物改造 效果越好。Abstract: Biodegradation on coal has attracted extensive attention from scholars worldwide for its advantages of in⁃ creasing gas content, porosity, and desorption. To explore coal reservoir microscopic pore structure evolution dur⁃ ing the process of biodegradation, taking a case of the Jurassic coal in the Huangling mining area at the southern mar⁃ gin of Ordos basin, the coal pore structure in situ is compared with that of after⁃degradation using field emission scan⁃ ning electron microscopy (FE-SEM) technology. Direct evidence of biodegradation on the coal surface is discovered. Based on the image binarization and box⁃dimension fractal method, the fractal dimension variation of coal reservoir pore structure before and after biodegradation is quantitatively characterized. The results show that the pores and fis⁃ sures of raw coal samples in the Huangling mining area are well developed. The primary pores are dominated by gas holes, while the secondary pores are mainly composed of crushed, brecciated, and friction pores. The exoge⁃ nous fractures are dominated by cracks with a width of 1-2 μm. After biodegradation, the shape and size of pores in the coal reservoir are changed, and the pores diameter increases. Under the action of biodegradation, the organic matter of coal becomes loose and a large number of intergranular pores are regenerated. Crawling traces of microbial activity are found on the surface of the coal matrix, supplying the direct evidence of microbial action on coal surface. After bio⁃ degradation, the fractal dimension of the coal pore structure decreases, the coal surface becomes smooth, and the pores’structure become simple. The value of original fractal dimension is positively correlated with its variation, indica⁃ ting that the more complex the original pore structure of a coal reservoir, effect of the better the microbial modification.