黔西北地区石炭系祥摆组页岩微观孔隙结构及分形特征

doi:10.19657/j.geoscience.1000-8527.2022.201

摘要/Abstract

摘要：

为研究海相含煤地层页岩的微观孔隙特征,选取黔西北地区石炭系祥摆组页岩作为研究对象,利用扫描电镜(SEM)和液氮吸附实验研究孔隙特征,同时研究其分形特征,并探讨孔隙结构的影响因素。研究结果表明:研究区石炭系祥摆组页岩在扫描电镜下可观察到4类微观孔隙(粒内孔、粒间孔、有机质孔、微裂缝),其中微裂缝、有机质孔发育较丰富,具有较强的生成烃类气体能力和良好的储集性能;液氮吸附等温线在形态上呈反“S”形,表明中孔在微观孔隙中最为发育,滞后回线类型主要为H2型的细颈广体的墨水瓶孔;BJH总孔体积和BET比表面积值均较大,平均值分别为0.0155 cm³/g和13.20 m²/g,平均孔径为6.22 nm,纳米级微观孔隙大量发育,为烃类气体提供丰富的储集空间;页岩样品微观孔隙结构分形维数D较大,主体大于2.723 2,反映出孔隙结构复杂、非均质性较强;BET比表面积与TOC、石英含量呈一定的负相关性,与分形维数呈一定的正相关性;平均孔径值与石英含量正相关性较好,与分形维数负相关性较好,与黏土矿物含量呈一定的负相关性。石炭系祥摆组页岩微观孔隙的BET比表面积较大、平均孔径较小,微观孔隙结构较为复杂。

关键词: 黔西北, 祥摆组, 富有机质页岩, 微观孔隙结构, 分形理论

Abstract:

To study the microscopic pore characteristics of shale in marine coal-bearing strata, we studied the Carboniferous Xiangbai Formation shale in northwestern Guizhou, and used SEM and N₂ adsorption analyses and fractal theory to study its fractal characteristics. We then explore the influencing factors of microscopic pore structure. The results show that four types of pores can be identified (intragranular, intergranular, organic matter and micro-fracture pores), a large number of microfractures and organic matter pores are developed, which have strong hydrocarbon generating ability and good reservoir performance. The adsorption isotherms of N₂ show an inverse S-type, indicating that the adsorption isotherms were mainly mesopores. The hysteresis loops formed by adsorption isotherms and desorption isotherms were mainly H2-type thin-necked wide-body ink bottle pores. The specific surface area is large (average 13.20 m²/g), and the total pore volume is large (average 0.015 5 cm³/g). The average pore size is 6.22 nm and the massive development of nano-scale micropores would provide rich reservoir space for hydrocarbon gases. The fractal dimension D of microscopic pore structure of shale samples is larger (average 2.723 2), reflecting strong heterogeneity of pore structure. BET specific surface area shows negative correlation with TOC and quartz content, and positive correlation with fractal dimension. The average pore size has good positive correlation with the quartz content, strong negative correlation with fractal dimension, and moderate negative correlation with clay mineral content. Larger BET specific surface area and smaller average pore size correspond to larger fractal dimension and more complex pore structure.

Key words: northwestern Guizhou, Xiangbai Formation, organic-rich shale, microscopic pore structure, fractal theory

中图分类号:

TE132.2

姜秉仁, 邓恩德, 韩明辉, 马子杰. 黔西北地区石炭系祥摆组页岩微观孔隙结构及分形特征[J]. 现代地质, 2022, 36(04): 1065-1073.

JIANG Bingren, DENG Ende, HAN Minghui, MA Zijie. Microscopic Pore Structure and Fractal Characteristics From the Carboniferous Xiangbai Formation Shale in Northwestern Guizhou[J]. Geoscience, 2022, 36(04): 1065-1073.

图/表 9

图1 研究区位置图[13]

Fig.1 Location map of the study area

图2 石炭系祥摆组页岩样品镜下微观孔隙类型及特征

Fig.2 Microscopic pore types and characteristics of shale samples from the Carboniferous Xiangbai Formation

图3 典型石炭系祥摆组页岩样品吸附-脱附曲线

Fig.3 Adsorption-desorption curve of typical shale samples from the Carboniferous Xiangbai Formation

图4 石炭系祥摆组页岩样品孔径分布图

Fig.4 Pore size distribution of shale samples from the Carboniferous Xiangbai Formation

表1 基于N2吸附法的页岩微观孔隙分形维数

Table 1 Fractal dimension of shale micro-pores based on N2 adsorption

样品编号	线性拟合方程	D	R²
XB-1	y=-0.2611x + 1.6284	2.738 9	0.976 8
XB-2	y=-0.1586x + 1.2983	2.841 4	0.991 7
XB-3	y=-0.2440x + 1.6505	2.756 0	0.974 7
XB-4	y=-0.2731x + 1.4773	2.726 9	0.973 9
XB-5	y=-0.3069x + 1.6567	2.693 1	0.977 9
XB-6	y=-0.2868x + 1.5138	2.769 9	0.986 8
XB-7	y=-0.2301x + 1.5559	2.769 9	0.987 0
XB-8	y=-0.5784x - 0.0422	2.421 6	0.972 4
XB-9	y=-0.2730x + 1.4160	2.727 0	0.983 2
XB-10	y=-0.2398x + 1.5872	2.760 2	0.980 0
XB-11	y=-0.2667x + 1.4757	2.733 3	0.979 0
XB-12	y=-0.2586x + 1.4056	2.741 4	0.989 8

图5 典型石炭系祥摆组页岩样品分形曲线图

Fig.5 Fractal curve of typical shale samples from the Carboniferous Xiangbai Formation

图6 石炭系祥摆组页岩孔隙结构参数与TOC的关系

Fig.6 Relationship between pore structural parameters and TOC of the Carboniferous Xiangbai Formation shale

图7 石炭系祥摆组页岩孔隙结构参数与矿物成分的关系

Fig.7 Relationship between pore structural parameters and mineral composition of the Carboniferous Xiangbai Formation shale

图8 石炭系祥摆组页岩孔隙结构参数与分形维数的关系

Fig.8 Relationship between pore structural parameters and fractal dimension of the Carboniferous Xiangbai Formation shale

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