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页岩孔隙结构及差异性是页岩含气性和产能评价的基础性问题.针对川东南彭水地区五峰组与龙马溪组页岩的孔隙结构已有若干研究成果,然而在页岩孔隙结构差异性和有机孔定量特征方面还缺乏研究.利用低温低压氮气吸附测定和氩离子抛光-场发射扫描电镜(FE-SEM)技术,对页岩样品纳米孔隙进行了二维观察与统计以及分形特征计算,研究了3nm至几百nm页岩孔径范围的孔隙结构及其差异性.研究区五峰组-龙马溪组页岩有机孔十分发育;氮气吸附测定页岩孔隙形状包含开放型圆筒状、层状结构狭缝状和墨水瓶状等;扫描电镜观察有机孔形态主要有近圆形、椭圆形和多角形等.五峰组和龙马溪组页岩孔隙结构具有明显的差异性,主要体现在孔径大小、形态和数量上.氮气吸附测定表明,五峰组页岩孔隙比表面积和总孔容较龙马溪组大,微孔所占总孔的比例也较高;五峰组页岩孔径相对龙马溪组更细窄.扫描电镜二维图像观察与统计结果表明,五峰组有机孔径以小于35nm为主,形态以多角形为主;龙马溪组有机孔径以小于50nm为主,形态多呈近圆形和椭圆形.五峰组页岩的分形维值大于龙马溪组页岩,说明前者孔隙复杂程度较高.
The pore structure and the difference of shales are the basic problems of shale gas and productivity evaluation.According to the research results on the pore structure of shale in Wufeng Formation and Longmaxi Formation in Pengshui area of southeast Sichuan Province, The differences and the quantitative characteristics of organic pores are still lacking.The two-dimensional observation and statistics of nano-pores of shale samples and the fractal features were carried out by using low temperature and low pressure nitrogen adsorption measurement and argon ion polishing-field emission scanning electron microscope (FE-SEM) The pore structures and their differences in shale pore size range from 3 nm to several hundreds nm were calculated and studied.The organic pores of shale in Wufeng Formation and Longmaxi Formation of the study area developed well.The pore shape of shale samples was determined by nitrogen adsorption including open cylinder, Layered structure slit shape and ink bottle shape, etc. The morphology of organic pores observed by scanning electron microscope mainly includes the shape of circle, ellipse and polygon, etc. The pore structure of shale in Wufeng Formation and Longmaxi Formation is obviously different, Pore size, shape and quantity.The results of nitrogen adsorption show that the specific surface area and total pore volume of shale in Wufeng Formation are larger than those in Longmaxi Formation, and the proportion of micropores in total pores is also higher. The rock pore size is narrower than that of Longmaxi Formation.The observation and statistical results of two-dimensional scanning electron microscopy show that the organic aperture of Wufeng Formation is dominated by less than 35nm and the polygons are the major ones in the Wufeng Formation. The organic apertures in the Longmaxi Formation are dominated by less than 50nm, Mostly round and oval.The fractal dimension of the Wufeng shale is larger than that of the Longmaxi Formation, which indicates that the pore complexity of the former is higher.