Abstract: Oil and gas exploration operations in Huanghekou Sag, Bohai Bay Basin have been mainly conducted in the structural ridge in the central and steep slope zone in the north for a long time. The slope zone is not well explored or understood, and hydrocarbon accumulation and enrichment there is not clear. Based on the characteristics and differences in terms of four aspects of the slope zone including internal fault-slope combination, sedimentary characteristics, slope gradient and tectonic evolution, the southern slope zone of Huanghekou west subsag and the southern slope zone of Huanghekou central subsag can be classified as two categories: synsedimentary micro-oblique ramp type slope zone and synsedimentary stable fault terrace type slope zone. Different structural styles are developed in different types of slope zones which have significant differential controlling effect on the distribution of sedimentary system and hydrocarbon transport, accumulation and enrichment. Synsedimentary micro-oblique ramp type slope zone is of the “horizontal and stepwise” hydrocarbon transport model, where Neogene Minghuazhen formation is the dominant hydrocarbon enrichment series. During stepwise hydrocarbon transport, hydrocarbon accumulation series was lifted step by step and hydrocarbon accumulation horizon is shallower in higher positions of slope zone. Synsedimentary stable fault terrace type slope zone is of the “vertical through-going” hydrocarbon transport model, where hydrocarbon accumulation is close to the source, with high hydrocarbon abundance and deep-shallow composite hydrocarbon accumulation characteristics. On the plane, the bent pressurized section in principal faults of slope zone is hydrocarbon enrichment zone. These understandings provide a basis for further exploration.

Key words: slope zone type, differential reservoir controlling effect, enrichment pattern, continental faulted basin, the Huanghekou sag