Samples from the lower Paleozoic marine shales and Mesozoic continental shale in the middle and upper Yangtze region were taken to investigate the structural characteristics and the thermal evolution of nanoporosity in shales using argon-ion milling technology,field emission scanning electron microscopy (FE-SEM) and low-pressure N2 adsorption experiments.The results indicate that there are four major pore types in the shales,including organic nanopores,interparticle pore,intraparticle pores as well as microfractures.TOC and Ro are the key factors controlling the development of nanoporosity volumes.For high thermal evolution shales,the order of the development extent of organic nanopores in different types of kerogen is type Ⅰ＞type Ⅱ ＞type Ⅲ.Quartz and clay minerals have indirect effects on the development and distributions of nanoporosity by controlling changes in TOC.Pore-size distributions and relative proportions of micropores,mesopores,and macropores are affected by thermal maturity evolution.During the high-over mature stage of shale,micropores and mesopores associated with organic matter have continuously increased with the raising thermal maturity.Under the condition of extremely high thermal maturity,the macroporous in the shales are transformed into mesopores and micropores,and the organic nanopores decrease,causing nanopore volume to be displayed a decreasing trend after the first increase with increasing thermal maturity.Thermal cracking gas and methanation of kerogen and soluble bitumen in shales can be the main reasons for organic nanoporosity formation.%以中、上扬子地区下古生界海相和中生界陆相页岩为研究对象,运用氩离子抛光-场发射扫描电子显微镜技术和氮气吸附实验测试技术对页岩储层的纳米级孔隙发育特征及热成熟演化进行探讨.结果表明:页岩主要发育了有机质孔、粒间孔、粒内孔和微裂缝等4种孔隙类型;TOC和Ro是控制页岩纳米级孔隙发育的主要因素;对于高演化页岩,不同干酪根类型的有机质孔隙发育程度的大小次序为Ⅰ型＞Ⅱ型＞Ⅲ型;石英和黏土矿物通过控制TOC的变化对纳米级孔隙发育和分布产生间接影响;页岩热成熟度演化影响页岩孔径分布和微孔、中孔和大孔相对含量的变化,在高—过成熟阶段,与有机质有关的微孔、中孔呈不断增加的趋势,在极高成熟度阶段,页岩大孔转变为中孔和微孔,有机质孔隙变小,纳米级孔隙体积呈现出先增加后减小的趋势;页岩中干酪根、可溶沥青热裂解生气作用和甲烷化作用可能是页岩有机质纳米级孔隙形成的主要原因.
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