Tracing migration pathways by integrated geological, geophysical, and geochemical data: A case study from the JX1-1 oil field, Bohai Bay Basin, China

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 (E(2)s(3), E(2)s(1), and E(3)d(3)) exist in the Liaodong Bay subbasin, and crude oil in the JX1-1 field was derived from the E(2)s(3) and E(2)s(1) source rocks. The carrier beds from E(2)s(3) and E(2)s(1) source rocks to the trap were characterized using geophysical data. The fan-delta sandstone in the E(2)s(3) Member has an immediate contact with E(2)s(3) source rock and served as dominant conduit for the expulsion and migration of oil generated from E(2)s(3) source rock. The E3d3 braided-delta sandstones overlying the E(2)s(1) source rock served as dominant conduit for E(2)s(1)-sourced oil. The focusing of petroleum migration pathways and the merge of migration pathways in E(2)s(3) and E(3)d(3) sandstones account for the accumulation of the JX1-1 field and the mixing of E(2)s(3)- and E(2)s(1)-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.