Abstract:

The development and evolution of the fault systems not only shaped the formation process and geological structure of the paleo-buried hills, but also profoundly influenced the hydrocarbon accumulation regularity within the buried hills. Focusing on the Paleozoic-Mesozoic buried hills in the Yidong area of the Bohai Bay basin, this study systematically characterizes the stratigraphic structure and tectonic patterns of the buried hills, and further investigates the differential development characteristics and spatiotemporal evolution of the fault systems. The formation processes and current structural configuration of the paleo-buried hills are clarified through balanced section restoration, further exploring the mechanisms of hydrocarbon migration, accumulation, and reservoir formation within the paleo-buried hills. The research results show that: The Meso-Paleozoic strata in the Yidong area can be divided into two major tectonic layers and four tectonic sub-layers. The stratigraphic structure of the hills is predominantly characterized by dual and multiple tectonic layers, though some remnants of single tectonic layers are still present. The formation of the Yidong paleo-buried hills underwent multiple phases of subsidence, uplift, and denudation from Mesozoic to Cenozoic, responding to the combined action of compression, extension and strike-slip movements associated with three sets of fault systems oriented NW, NNE-N, and NEE-E. The hydrocarbon reservoirs in paleo-buried hills are characterized by multiple oil-bearing layers, distribution along faults and separation by internal faults. The hydrocarbon accumulation rules are jointly determined by factors such as source-aligned faults, lateral hydrocarbon connection windows, and internal faults.

Key words: paleo-buried hills, fault system, mountain-forming process, reservoir-forming rule, Yihezhuang uplift, Jiyang depression