The Nanpu Sag is one of the 50 sub-basins of the greater Bohai Bay basin in northeast China. Three petroleum systems have been identified in the sag through both 2-d and 3-d seismic interpretations, high-resolution well log correlation, and geochemical studies. The petroleum system of the Gaoshangpu-Liuzan area has been well explored and is a good analog for the Beipu-Laoyemiao system in the onshore and the Laopu-Getuo system in the shallow water transition zone. The Eocene-Oligocene syn-rifting lacustrine sands and sub-aqueous fans are the major reservoir rocks. They have porosities of 15-20% and permeabilities of 10-500 md. Fractured Cambrian-Ordovician carbonates and Eocene bioclastic limestones and grainstones are also excellent reservoirs. Dark lacustrine mudstones of the Eocene Shahejie Formation are organic-rich and have TOC typically ranging from 1.5% to 6%. They were deposited during the rapid subsidence of the basin associated with the subduction of the Pacific Plate under the Eurasian plate. Characterization of reservoired hydrocarbons and source rock organic matter show oil generation from Types II-III with expulsion at moderately high maturities. Migration of hydrocarbon into the Gaoshangpu High and Beipu High from the kitchen of the Shahejie Formation was facilitied by the Gaoliu and Baigezhuang faults. Migration to the Laupu-Getuo Strcutural Zone was mainly made possible by small faults, microfractures, and basin floor sands. Trapping is a combination of tilted block fault closure, extensive spread of Oligocene Dongying prodelta shale, and basaltic layers of usually 10 to 100 m thick.

AAPG Search and Discovery Article #90937©1998 AAPG Annual Convention and Exhibition, Salt Lake City, Utah