Relationship Between Fluvial Architecture and Remaining Oil in the Gudong Oilfield, Bohai Basin, China

Xiangyun Jiang¹, Shenghe Wu², and Diyun Yu^3
1Institute for Geophysics, University of Texas at Ausin, Austin, TX
²Faculty of Geoscience, China University of Petroleum, Beijing, Beijing, China
³Shenyang Producting Department of Liaohe Oilfield Branch Company, PetroChina, Shenyang, China

Most oil in the Bohai basin is found in sandstone deposited in meandering Mio-Pliocene fluvial channels. Unfortunately, water cuts are high (90%) and oil recovery ratios are low (30%) because of the complex architectures of these fluvial reservoirs. In this study, we use the “fitting model” method to analyze hierarchic architectures, including point bar and point bar inner. Using available dense well (150mx150m well spacing )and seismic data along with analog data from outcrop and modern river systems, we infer that the Mio-Pliocene fluvial system at the Gudong oil field is dominated by a large, 1430-m-long and 2400-m-wide point bar. The point bar is formed by a 300-m-wide high sinuosity channel. The derived geologic model predicts the following characteristics of the point bar inner: 1) parallel-inclined lateral accretion layers composed of shale; 2) 200m width of single lateral accretion body; 3) 3~5 degree dig angle of lateral accretion surfaces. Our model predicts that 13 lateral accretion layers are distributed over a vertical section of 2000 m in the Gudong oil field and individual lateral accretion layer is less than 300m in a vertical profile. The combining of the architecture model and well testing data indicates that the remaining oil is influenced by the relationship between the lateral accretion layer and the perforated intervals in a sandbody. Future exploration can target these accretion layers which form stratigraphic traps for remaining oil. The method described in this study can be applied to other mature oil fields in stratigraphically complex settings.

AAPG Search and Discover Article #90078©2008 AAPG Annual Convention, San Antonio, Texas