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 Es

3

and Es

4

.Oils in the steep slope belt and central tectonic belt were derived from Es

4

source rocks in the main sag

while oils in the gentle slope belt originated from the Es

4

source rocks both in the main sag and in the south subsag.(2) During Es

4

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 Es

4

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.