Abstract The late Ordovician Wufeng and early Silurian Lungmachi formations are primary targets for shale gas exploration in the southeastern marginal area of the Sichuan Basin, Southwest China. In this research, different groups of micro-fossils (large numbers of taxonomically unrelated organic- and inorganic-walled fossil groups) from the two formations were analyzed in order to investigate their pore characters under the evaluation of shale gas reservoirs. A large number of biological autologous micro-nano pores in radiolarians, sponge spicules, acritarchs, conodonts, chitinozoans, and scolecodonts were analyzed. The results show that most pores are densely and randomly distributed with honeycomb or irregular shapes. Although the samples are over mature and were deeply buried, micro-fossils remain in a large number of biological micro-nano pores. Pore diameter varies from 20 to 4000 nm but differs among micro-fossil groups. The widely distributed siliceous micro-fossils, such as radiolarians and sponge spicules, could enhance the brittleness of shales. They may promote the development of natural fractures during diagenesis or artificial fractures during stimulation. When fractures are connected with micro-nano pores in the shale, they could provide effective storage space and improve the overall connectivity. In most of the analyzed shale samples, micro-fossils show positive correlation with high TOC strata. Considering the importance of micro-fossils and their pores in the perspective of hydrocarbon generation, connectivity, accumulation, and production of shale gas, we suggest that micro-fossil pores should be included in the classification of pore systems.

中文翻译：

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华南晚奥陶世—早志留世黑色页岩孢粉学分析为页岩气储层孔隙系统研究提供新思路

摘要 晚奥陶世五峰组和早志留世龙马池组是四川盆地东南缘地区页岩气勘探的主要目标。在这项研究中，分析了来自两个地层的不同微化石群（大量在分类学上无关的有机和无机壁化石群），以研究它们在页岩气储层评价下的孔隙特征。分析了放射虫类、海绵骨刺类、牙形类动物、牙形动物类、几丁质类动物和蛔虫类中的大量生物自体微纳米孔。结果表明，大部分孔隙呈蜂窝状或不规则状密集且随机分布。虽然样品已经过成熟，埋藏很深，微化石残留在大量生物微纳米孔隙中。孔径从 20 到 4000 nm 不等，但因微化石群而异。广泛分布的硅质微化石，如放射虫和海绵骨针，可以增强页岩的脆性。它们可能会促进成岩过程中天然裂缝的发展或刺激过程中人工裂缝的发展。当裂缝与页岩中的微纳米孔隙相连时，可以提供有效的储集空间，提高整体连通性。在大多数分析的页岩样品中，微化石与高 TOC 地层呈正相关。考虑到微化石及其孔隙在页岩气生烃、连通、聚集和生产方面的重要性，