Distribution Characteristics and Origin of Oilfields in Shijiutuo Uplift, Bohai Bay Basin, China

Abstract

The Shijiutuo uplift is one of the petroliferous belts in the Bohai Bay Basin, it is located to the southwest of the Qinnan depression, and to the north of the overpressured Bozhong depression. Three organic-rich, oil-prone source rock intervals exist in the two depressions, each of which has a distinct biomarker assemblage and each of which in the two depressions is difficult to be distinguished only by geochemical method because of similar geochemical characteristics. Combining organic geochemistry together with basin modeling, oil-source rock correlations of Shijiutuo uplift have been systematically studied in this paper. The third member of the Dongying formation (E3d3) is type II –III kerogen with lowest organism abundance, the first and second member of the Shahejie formation (E2s1+2) is type I kerogen with highest organism abundance, the third member of the Shahejie formation (E2s3) is type II kerogen. Carbon isotope of all oil of the Shijiutuo uplift is heavier than −27‰, which shows shijiutuo uplift is not E3d3-sourced oil; medium C30 4-methyl sterane abundance medium-high gammacerane abundance indicate that the oil of shijiutuo uplift is E2s1+2-sourced oil and E2s3-sourced oil; the oil of the northeast of Shijiutuo uplift is particular because of C29 preference. The simulation of migration in Qinnan depression shows that the oil in the north of the east pitching end of the uplift was charged from west-sub-sag of the Qinnan depression where large thickness of E2s1+2 strata remained; the oil in the northeast of Shijiutuo uplift was mainly charged from the deep area of the Qinnan depression and partially charged from the west-sub-sag. The simulation of migration in the Bozhong depression and Shijiutuo uplift shows that the oil in Bozhong depression mainly migrated laterally under overpressured layer, and then migrated vertically to the shallow layer through the uplift's boundary faults which can cause the release of the overpressure, finally accumulated in the uplift. In summary, the results show that most part of the oil in Shijiutuo uplift consists of E2s3-sourced oil and few E2s1+2-sourced oil of the Bozhong depression; oil in the northeast of Shijiutuo uplift consists of E2s3-sourced oil of the deep area in the Qinnan depression and partial E2s1+2-sourced oil of the west-sub-sag; oil in the north of the east pitching end of Shijiutuo uplift consists of E2s3-sourced oil and mass of E2s1+2-sourced oil of the west-sub-sag in the Qinnan depression.

AAPG Datapages/Search and Discovery Article #90189 © 2014 AAPG Annual Convention and Exhibition, Houston, Texas, USA, April 6–9, 2014