Petroleum System Evolution and Hydrocarbon Charge in the Nam Con Son Basin, Offshore Vietnam: Insights From 3D Basin Modelling and Sensitivity Analysis

Understanding hydrocarbon charge in structurally complex rift basins requires constraining the temporal and spatial relationships among source‐rock maturation, hydrocarbon generation and expulsion, migration pathways, trap development, reservoir architecture and fault behaviour. This study investigates petroleum‐system evolution in an anonymized structural cluster of the central Nam Con Son Basin, offshore Vietnam, using integrated well, geochemical, seismic and three‐dimensional basin‐modelling data. The model incorporates Oligocene–Lower Miocene source‐rock intervals, Miocene sandstone reservoirs, regional and local seals, structural framework and fault‐controlled migration pathways. The H150 source interval, including shale and coal facies, constitutes the dominant modelled source system, with H125 shale providing an additional contribution. Modelling indicates that the H150 shale entered the main oil window at approximately 13 Ma, with deeper source‐rock sections undergoing earlier expulsion during the Late Miocene and intermediate‐depth mature intervals contributing progressively during the Quaternary. Modelled H150 shale generation ranges from approximately 0.5 to 138 kg m −2 for oil and up to 230 kg m −2 for gas. Hydrocarbons migrated from adjacent depocentres toward structural highs through a combination of carrier beds and faults and accumulated mainly within the H100 and H80 reservoir systems. Comparison with the reconstructed structural history indicates that many principal traps were established before or during the main charge interval, whereas continued fault reactivation created potential for local bypass, remigration or loss. Sensitivity analyses show that neither uniformly enhanced source‐rock richness nor end‐member fully open or fully sealing fault configurations satisfactorily reproduce the available hydrocarbon distribution. The principal contribution is therefore the combined evaluation of charge timing, model‐observation mismatch and fault‐state sensitivity. The available observations are more consistent with spatially variable fault connectivity and temporally variable preservation of hydrocarbon accumulations than with either uniform fault behaviour or source richness alone.