Normal-pressure shale gas reservoirs are widely distributed in south-eastern Chongqing and show good potential for resource exploration. This paper reports the organic matter (OM), physical, and pore characteristics, mineral composition, and gas content of representative shale samples from the Upper Ordovician Wufeng Formation and Member 1 of the Lower Silurian Longmaxi Formation (Long 1 Member). Microscopic pores within different shale layers of the Long 1 Member were classified, quantitatively evaluated, and their development mechanisms were systematically studied. We found that OM characteristics, mineral composition, and pore type were the main factors affecting the enrichment and preservation of shale gas. The characteristics of the Long 1 Member are mainly controlled by changes in the sedimentary environment. There are evident differences in total organic carbon content and mineral composition vertically, leading to a variable distribution of pores across different layers. Organic matter abundance controls the degree of OM pore development, while clay minerals abundance control the development of clay mineral-related pores. Total organic carbon content generally controls the porosity of the Long 1 Member, but clay minerals also play a role in OM-poor layers. Pore connectivity and permeability are influenced by the development of pores associated with brittle minerals. We propose a microscopic pore development model for the different layers. Combining geochemical data and this pore development model, layers 1–4 are considered to be excellent shale gas preservation and enrichment reservoirs. Poor preservation conditions in layers 5–7 result in high levels of shale gas escape. Layers 8–9 possess a better sealing condition compared with layers 5`-7 and are conducive to the enrichment and preservation of shale gas, and can thus be used as future potential target strata. This research provides a theoretical basis for exploring and evaluating shale gas potential in the studied region or other complex normal-pressure shale blocks.

渝东南地区常压页岩气藏分布广泛，资源勘探潜力巨大。本文报道了上奥陶统五峰组和下志留统龙马溪组一段（龙一段）代表性页岩样品的有机质（OM）、物理和孔隙特征、矿物组成和气体含量。对龙一段不同层位页岩微观孔隙进行分类、定量评价，系统研究其发育机制。研究发现，有机质特征、矿物成分和孔隙类型是影响页岩气富集和保存的主要因素。龙1段特征主要受沉积环境变化控制。总有机碳含量和矿物成分在垂直方向上存在明显差异，导致不同层位孔隙分布存在差异。有机质丰度控制着有机质孔隙的发育程度，而粘土矿物丰度则控制着与粘土矿物相关的孔隙的发育程度。总有机碳含量通常控制着龙一段的孔隙度，但粘土矿物在贫有机质层中也发挥着作用。孔隙连通性和渗透性受到与脆性矿物相关的孔隙发育的影响。我们提出了不同层的微观孔隙发育模型。结合地球化学数据和该孔隙发育模型，认为1-4层是优良的页岩气保存和富集储层。第 5-7 层保存条件差导致页岩气大量逃逸。8~9层相对5`-7层具有更好的封闭条件，有利于页岩气的富集和保存，可作为未来潜在的目的层系。该研究为研究区或其他复杂常压页岩区块的页岩气潜力勘探与评价提供了理论依据。