Characteristics and Accumulation Modelsof the WholePetroleumSystem in Paleogene Hetaoyuan Formation, Biyang Depression

　　[Objective]As a typical hydrocarbon-rich sag in the eastern rift basins of China, the Biyang Depression requires a systematic investigation into the key controlling factors, reservoir types, and hydrocarbon accumulation and enrichment patterns within its whole petroleum system.[Methods]To address this, this study integrates multidisciplinary data from drilling, logging, and geochemistry with regional exploration history to systematically characterize the system.
　　[Results]The results demonstrate that the Paleogene Hetaoyuan Formation in the study area presents superior geological conditions for the development of a complete petroleum system. The source rocks are characterized by Type Ⅰ and Type Ⅱ₁ organic matter, whose parent materials are dominated by cyanobacteria and structured alginite, exhibiting a high hydrocarbon generation potential with yields reaching up to​ 630 kg/t. This provides an abundant material foundation for sustained hydrocarbon charging in the whole petroleum system. Multi-type reservoir spaces facilitate hydrocarbon accumulation, resulting in the orderly zonal occurrence of shale oil, dolomite oil, tight oil, and conventional oil reservoirs extending from the hydrocarbon-generating center to the basin margin.[Conclusion] Based on the analysis of the integrated petroleum system, three typical accumulation models were identified: (1)the Northern Slope Belt – distal source – complex structural zone accumulation model; (2)the Central Sag Belt – intra-source and near-source – multi-type accumulation model; (3)the Southern Steep Slope Belt – near-source – lithologic updip pinch-out zone accumulation model. These distinct yet interconnected models constitute the subsystems of conventional and unconventional reservoirs within the integrated petroleum system.Furthermore, this systematic study provides a robust theoretical basis for the efficient exploration of remaining petroleum resources and the rapid discovery of new exploration domains in highly mature exploration areas.