Abstract: Currently, the scarcity of offshore drilling and rapid lateral variations in reservoirs results in lower characterization accuracy, adversely impacting recoverable reserve calculations. As exploration and development continue to break through depth limitations, refined reservoir characterization and sweet spot prediction become critical for deep hydrocarbon development. Local and regional seismic and geological data were analyzed by applying seismic sedimentology, from which horizontal sedimentary facies distribution and vertical evolution patterns in the study area were clarified. In addition, channel episode division and connectivity analysis were conducted based on reservoir geological structure, and sweet spot was predicted under the guidance of geological models of sweet spot development by characterizing physical properties of sweet spot indicators. Resuklts show that the studuy area featured fluvial-dominated deposits, and units H6&H10 (meandering river), H7 (straight river), and H12 (braided river) were specified in sedimentology. Units H6, H7, and H10 are structural-lithologic gas reservoirs exhibiting local discontinuity due to channel stacking and Unit H12 is a structural gas reservoir. Zones below Units H7S host sweet spot, for which a development model of "coupling paleo-structures, intense fractures, and main channels" was established for the northern study area. Therefore, integrating seismic-geological technique could enhance reservoir and sweet spot description accuracy, by which recoverable reserve assessment and development planning has been well guided for the N gas field, providing significant insights for exploring structural-lithologic flank zones and deep layers in offshore less-drilling regions.