Abstract: To elucidate the controlling effect of silica diagenesis on pore development in shale reservoirs, a case study was conducted on the Upper Ordovician Wufeng Formation and Lower Silurian Longmaxi Formation shales from the southern and northeastern Sichuan Basin. Based on rock thin section observation, scanning electron microscopy-cathodoluminescence (SEM-CL) analysis, elemental geochemical analysis, and thermal simulation experiments, the study investigates the silica diagenetic process and the formation and evolution of organic pores within the silica framework. The research findings show as follows. (1) In the siliceous shale of Wufeng Formation and Longmaxi Formation, biogenic quartz is the predominant silica-rich mineral. Quartz of different genetic types exhibit district cathodoluminescence (CL) emission peak patterns at wavelengths of approximately 420 nm and 570 nm. Furthermore, the transformation of opal-CT and chalcedony into micron-size authigenic quartz further exacerbates the lattice defects associated with the emission peak at around 570 nm. (2) The substantial presence of solid bitumen within the silica framework serves as the primary carrier for organic pore, with its content being the most significant factor influencing organic pore formation. (3) The authigenic microcrystalline quartz and aggregates formed during the mesogenetic A stage retain internal pores that can provide space for oils generated by the pyrolysis of organic matter. These pores also play a supporting role in the formation of organic pore networks through the conversion of liquid hydrocarbons into solid bitumen. (4) The total organic carbon (TOC) content in shale shows a trend of first increasing and then decreasing with the increase of SiO₂ content. The highest TOC content, primarily ranging from 3.0%to 6.0%, is observed when the SiO₂ content is between 70%and 80%, which is most favorable for pore development. The findings provide theoretical support for advancing the study of the organic-inorganic synergistic evolution process in shale and reveal the formation mechanisms of shale oil and gas reservoirs.

Key words: organic-rich shale, silica diagenesis, shale reservoir, organic-inorganic synergistic evolution, Sichuan Basin, Wufeng Formation, Longmaxi Formation

摘要： 为明确硅质成岩作用对页岩储层孔隙发育的控制作用,以四川盆地南部和东北部地区的上奥陶统五峰组和下志留统龙马溪组页岩为例,基于岩石薄片观察、扫描电镜-阴极发光联测、元素地球化学分析、热模拟实验等手段,开展了硅质成岩演化过程和硅质格架内有机质孔的形成与演化研究。研究结果表明:①五峰组和龙马溪组硅质页岩中的生物成因石英是主要的硅质矿物类型,不同成因类型的石英在波长约420 nm和570 nm处的阴极发光发射峰形态存在差异,由蛋白石-CT和玉髓转化为微米级自生石英的过程会进一步加剧与波长约570 nm发射峰相关的晶格缺陷;②硅质格架中发育的大量固体沥青是有机质孔的主要载体,其含量是有机质孔发育的最主要影响因素;③形成于中成岩阶段A期的自生石英微晶及聚集体,其内部保留的孔隙可为有机质热解生成的油提供储集空间,并为液态烃向固体沥青转化形成有机质孔网络起到了支撑作用;④页岩中的总有机碳(TOC)含量随SiO₂含量的增加呈先增加后减少的趋势,SiO₂含量为70%~80% 时的TOC含量最高且主体分布在3.0% ~6.0%, 最有利于孔隙发育。研究成果可为深化页岩的有机-无机协同演化过程研究、揭示页岩油气储层形成机理提供理论支撑。

关键词: 富有机质页岩, 硅质成岩作用, 页岩储层, 有机-无机协同演化, 四川盆地, 五峰组, 龙马溪组