This book focuses on the study of low permeability and tight sandstone reservoirs within fluvial delta facies found in the Ordos Basin, Songliao Basin, and Sichuan Basin. It systematically examines the superimposed patterns, geometric forms, and scale characteristics of sedimentary sand bodies within the fluvial delta system. Additionally, it analyzes the impact of seepage barriers such as interlayers and closed faults on fluid flow. The book establishes a sedimentary model for sand bodies in typical sedimentary environments, considering the differences in separation and connectivity caused by the shape, scale, direction, and spatial overlap of different reservoir units and seepage barriers. It investigates the mechanisms of fluid flow controlled by interlayer, plane, and intralayer heterogeneity to understand the fluid flow within the reservoir architecture unit affected by different flow types.