黔北地区牛蹄塘组海相页岩孔隙结构及其非均质性特征

The Pore Structure and Heterogeneity Characteristics of the Niutitang Marine Shales in the oNrthern Guizhou Area

利用氩离子抛光扫描电镜和氮气吸附法研究铜仁-毕节地区牛蹄塘组页岩的孔隙形态、孔径分布以及孔隙分形特征,讨论了页岩组分及孔隙结构参数对分形维数的影响。结果表明,牛蹄塘组页岩孔隙类型多样,包括有机质孔、粘土矿物层间孔和溶蚀孔等。页岩总孔体积介于0.0086~0.0313 cm^(3)/g,平均为0.0212 cm^(3)/g;BET比表面积介于5.64~24.61 cm^(2)/g,平均为17.23 cm^(2)/g,页岩具有不同的孔隙结构特征,进而表现出不同的孔隙非均质性。页岩孔隙具有明显的分形特征,分形维数D1介于2.0573~2.5254之间,受TOC和矿物组分的共同控制,与总孔体积和比表面积呈正相关性;分形维数D2介于2.6329~2.8028之间,主要受TOC影响,其与TOC、总孔体积和比表面积均呈现先增加后降低的趋势。页岩平均孔径越小,微孔越发育,分形维数越大,孔隙非均质性越强。

BIB-SEM observation and nitrogen adsorption method were applied to characterize the pore morphology, pore size distribution and fractal characteristics of the Niutitang shales in the Tongren-Bijie area. The relationships between the shale compositions, the pore structure parameters and fractal dimensions were investigated. The results show that Niutitang shales contain various pore types, including organic pore, clay mineral inter-layer pore and dissolution pore. The total pore volume is between 0.0086 cm^(3)/g and 0.0313 cm^(3)/g, with an average of 0.0212 cm^(3)/g;BET surface area ranges from 5.64~24.61 cm^(2)/g, with an average of 17.23 cm^(2)/g. Niutitang shales contain various pore structure and thus display different pore heterogeneity. Two fractal dimensions D1 and D2 were obtained,with D1 ranging from 2.0573 to 2.5254, and D2 between 2.6329 and 2.8028. D1 is common controlled by TOC and mineral composition, and displaying positive correlations with total pore volume and BET surface area, whereas D2 is mainly affected by TOC, and showing the tendency of first strengthened with increasing TOC, total pore volume and BET surface area, and then weakened. The smaller the average pore diameter, the more micropore development, the higher the fractal dimension, and the stronger the heterogeneity of pores.