Abstract: In Bohai Sea,large-scale high-sulfuric oilfields are only found in Laizhou Bay Sag.The crude oil properties in this area are complex,and the source and genesis of oil here are not clearly understood.We made a detailed study on the hydrocarbon sources and genesis of oilfields in Laizhou Bay Say by means of geochemical analysis and basin simulation,and incorporating a large number of experimental data.The results show that (1) there are two sets of effective source rocks developed in the sag,namely the Es³ and Es⁴.Oils in the steep slope belt and central tectonic belt were derived from Es⁴ source rocks in the main sag,while oils in the gentle slope belt originated from the Es⁴ source rocks both in the main sag and in the south subsag.(2) During Es⁴ sedimentary period,the waters of Laizhou Bay Sag were not connected,so that the south subsag waters were prone to become saline to produce sulfur-rich kerogens.Thus,the distribution of Es⁴ source rocks in the south subsag controls the distribution of high-sulfuric oil,serving as the major controlling factor for generating high-sulfuric oil.In addition,microbial degradation can lead to the thickening of crude oil,and cause the relative enrichment of sulfur in crude oil.(3) Kenli 16-1 oilfield is characteristic of late-stage hydrocarbon accumulation,with a hydrocarbon accumulation model of saline lacustrine basins featuring early generation,early expulsion,and dual-sag hydrocarbon charge.Meanwhile,the accumulation model of deep reservoirs is a typical example of a distal source charge through long distance oil migration along unconformity laterals,different from that of the shallow reservoirs.The Palaeogene formations in the southern south subsag and high reservoir quality buried-hill formations are regarded as favorable plays for hydrocarbon accumulation,which can be targeted for further oil and gas exploration.

Key words: oil source, source rock, biomarker compound, accumulation model, high-sulfuric heavy oil, Laizhou Bay Sag