Abstract: 3rd member of Shahejie Formation is contestable as hydrocarbon source rocks, though it is the main formation in which the lenticular lithologic reservoirs develop. In this paper, based on the theory of hydrocarbonexpulsion threshold, the hydrocarbonexpulsion characters and the potential source evaluation of the upper, middle, lower sections within the 3rd member of Shahejie Formation are discussed. In the upper, middle and lower sections within the 3rd member of Shahejie Formation, there were the same main period of hydrocarbon expulsion and the hydrocarbonexpulsion threshold depth of 2500m, 2650m, 2600m respectively. The total hydrocarbonexpulsion and the total sources in the three sections are 58.41×10⁸ t and 25.12×10⁸t, in which the lower section holds more 77%, and the middle and the upper sections hold 16% and 7% respectively. The conclusions can be made depending on the comprehensive analyses that the lower section is the one of the main hydrocarbon source rocks and the middle section, due to its little contribution to the lithologic pools, is not the main hydrocarbon source rocks in Dongying subdepression.

Key words: Dongying subdepression, the 3rd member of Shahejie formation, hydrocarbon source rocks, hydrocarbonexpulsion characters, resource evaluation