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Range of Secondary Hydrocarbon Generation of Paleogene Source Rock in Offshore Bohai Bay Basin, Eastern China

Abstract

Offshore Bohai Bay Basin was a Cenozoic multi-cycle, superposed basin. Paleogene source rocks are discovered mainly in the 3rd member of Eocene Shahejie Formation and the 3rd member of Oligocene Dongying Formation. Currently, most of the researches about secondary hydrocarbon generation in offshore Bohai Bay Basin sea focus on the mechanism and mode of hydrocarbon generation by using thermal simulation, but much less on its occurrence, distribution and influence factors. 2D and 3D seismics, cores, geochemical data, pressure data, and well testing data were used in the study. On the basis of research on tectonic evolution of Cenozoic basin, distribution and thermal evolution of Paleogene source rocks in offshore Bohai Bay Basin, the maturation history of source rocks was modeled through analyzing 150 typical wells of different tectonic units in the study area. Finally, various types of single well test data were used to validate the simulation results. The results showed that secondary hydrocarbon generation of source rocks in the 3rd member of Eocene Shahejie Formation was distributed in Liaoxi Low Rise, northern Liaodong Rise, Bodong Rise, Miaoxibei Rise, Bonan Low Rise, Laibei Rise and Shaleitian Rise. As to Oligocene Dongying Formation, secondary hydrocarbon generation of source rocks was distributed in inversion structure of Liaoxi sag, north-central Liaoxi low Rise, northern Bodong Rise, northern Bonan Rise and southern Laibei Low Rise. The areas of secondary hydrocarbon generation were mainly near the long-term inherited active fault zone. In addition, the Dongying movement at the end of Oligocene Dongying Formation deposition (Himalayan Movement Episode II) not only controlleds the range and size of secondary hydrocarbon generation, but also affected the start up of secondary hydrocarbon generation. In short, secondary hydrocarbon generation in offshore Bohai Bay Basin has a very important impact on the formation and distribution of oil and gas reservoirs, which is helpful to identify favorable exploration targets.