ABSTRACT

Tracing petroleum migration pathways is essential for predicting petroleum occurrence and reducing exploration risks associated with hydrocarbon charge, but a difficult task because of rapid lateral and vertical facies changes in lacustrine basins. An integration of geological, geophysical, and geochemical analysis is employed to investigate the origin of crude oil, the carrier-bed architecture, and migration pathways from source to trap in the JX1-1 oil field, Liaodong Bay subbasin, Bohai Bay Basin. Detailed geochemical studies suggest that three potential source-rock intervals (E2s3, E2s1, and E3d3) exist in the Liaodong Bay subbasin, and crude oil in the JX1-1 field was derived from the E2s3 and E2s1 source rocks. The carrier beds from E2s3 and E2s1 source rocks to the trap were characterized using geophysical data. The fan-delta sandstone in the E2s3 Member has an immediate contact with E2s3 source rock and served as dominant conduit for the expulsion and migration of oil generated from E2s3 source rock. The E3d3 braided-delta sandstones overlying the E2s1 source rock served as dominant conduit for E2s1-sourced oil. The focusing of petroleum migration pathways and the merge of migration pathways in E2s3 and E3d3 sandstones account for the accumulation of the JX1-1 field and the mixing of E2s3- and E2s1-sourced oil in the field. This study suggests that the distribution of permeable sandstones and their stratigraphic contact with the source rocks are key for petroleum migration and occurrence, and integration of geophysical, geological, and geochemical studies provide an effective way to trace petroleum migration pathways.

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