Abstract: Based on the abundant seismic, wells and geochemical data, studies were carried out on the formation mechanism and hydrocarbon accumulation controlling factors of sublacustrine fans of the third member of Dongying Formation in LD10 structural area, Liaozhong depression, Bohai Bay basin, and the hydrocarbon enrichment regularity was discussed. According to the research, the “chain island” type paleogeomorphology of Liaoxi uplift controlled the source condition, and the area near the main sand passages had a better development environment with bigger thicknesses and more periods. Single event fans and external configuration fans were confirmed by borehole seismic calibration, and boundary description methods were established by integration between geology and geophysics.  The deep structural background, the distance between the fans and source rock, and the pattern between the fault and the fans jointly controlled the hydrocarbon charging intensity in the LD10 structural area. Under the conditions of double deep ridges, smaller distance from the main source rock layers, and forward charging from fault to fans, the goal fans could form high hydrocarbon columns. These new understanding and methods were used to guide the exploration practice, with LD10-6 medium-large sublacustrine fans oilfield discovered in the Dongying Formation in the western slope of Liaozhong depression, which is a breakthrough in the exploration of sublacustrine fan of Paleogene in Bohai sea area.

Key words: Liaozhong depression, Dongying Formation, sublacustrine fan, slope zone, formation mechanism, hydrocarbon migration, Bohai Bay basin