Hydrocarbon accumulation model of the Mesozoic in Taibei Depression, western East China Sea

The East China Sea Shelf Basin is a Mesozoic-Cenozoic superimposed petroliferous basin formed upon a complicated Proterozoic-Paleozoic basement. It is rich in oil and gas resources and, therefore, of great significance to China's future energy strategy. The Mesozoic of the basin is expected to be a new oil and gas exploration target and even an important field in future in east China. The Taibei Depression is located in the southwestern Depression of the East China Sea Shelf Basin. In the Mesozoic continental fluvial and lacustrine depositional systems, there are two sets of source rocks: Fuzhou Formation mudstone and Shimentan Formation mudstone. Based on the static factors for hydrocarbon accumulation, such as source rocks, reservoir-cap assemblages and transportation systems in the Taipei Depression, through the analysis of the timing of source rock deposition and hydrocarbon accumulation, we studied the forming process of oil accumulations in the Taibei Depression. It is rather clear that the Fuzhou Formation and the Shimentan Formation are the main hydrocarbon sources. The sand bodies of the Fuzhou Formation, Shimentan Formation and Eocene Oujiang Formation are the main reservoirs. Oil and gas migrate along sand bodies and active faults around the margin of the depression. Early hydrocarbon accumulated in the pinch out of sandbodies and/or sealed by faults. Oil and gas readjustment and reaccumulation occurred in the whole basin while compression inversion happened by the end of Eocene to Oligocene. Finally, a reservoir-forming model for early and later adjustment of Mesozoic in the Taipei Depression is established.