Exploration in the area between Dingjiawuzi and Bamianhe tectonic zones has achieved a breakthrough in the east part of South Slope of Dongying sag. The Es4 oil and gas reservoir was found in Block Wang146. The reservoir has a burial depth of 1 462.9- 1 748.5 m, but the physical properties of crude oil shows the characteristic of high density, high viscosity and low freezing point, that is, a typical deep viscous oil reservoir. The formation mechanism of the reservoir is worth discussing. Based on the analysis of the information regarding the single well hydrocarbon and characteristics of the remarkable composition in the crude oil, it is clarified that the main source of hydrocarbon is generated in source rocks of Es4; during the process of migrating hydrocarbon outward from the oil-bearing depression, the degradation occurred; It is determined further that this area has 2 dominant hydrocarbon migration directions according to the differences in the degree of degradation of crude oil. The main migration path is along Dingjiawuzi structural trend, and another is along Bamianhe tectonic zones trend, and the degradation in the migration path of Dingjiawuzi structural trend is the strongest, therefore, it has caused the formation of the Es4 deep viscous oil reservoir in the Wang146 area. It is still of broad exploration prospects along the dominant hydrocarbon migration path.