Gravity-flow deposits and their exploration prospects in the Oligocene Dongying Formation, northwestern Bozhong Subbasin, Bohai Bay Basin, China

The E3d3 source rock has TOC contents in the range of 0.6-3.1%, Rock-Eval S2 values in the range of 0.7-19.8 mg HC/g rock, and Hydrogen indices (HI) in the range of 100-600 mg/g TOC. The E3d2L source rock has TOC contents ranging from 0.5 to 1.9%, Rock-Eval S2 values from 0.4 to 7.8 mg HC/g rock, and HI from 40 to 480 mg/g TOC. Both E3d3 and E3d2L source rocks have good hydrocarbon-generation potential. The E3d3 and E3d2L source rocks have entered the oil-generation peak window with the vitrinite reflectance (Ro) higher than 1.0%. Oils generated from the underlying source rocks shortly migrated to the overlying gravity-flow lithologic traps. The gravity-flow reservoirs could serve as potential and effective hydrocarbon exploration targets.