Control effects of petroleum biodegradation degree by bottom water and intercalation within oil reservoir

The research of the controls on the degrees of petroleum biodegradation within heavy oil reservoirs will benefit heavy oil reservoirs developing optimization and enhancing recovery efficiency. The characteristics of biodegradation of the saturated hydrocarbon for core extracts from the Liuhua11-1 reef reservoir are analyzed in this study, and the results show that bottom water and intercalation within the oil reservoir can significantly control the degree of petroleum biodegradation and affect the prediction of oil physical property. Liuhua11-1 reservoir has the one oil-water contact (OWC), with the hydrocarbon generated from the same source rock at similar high maturity and suffered from biodegradation less than level 6. Although the intercalations may lead to the occurrence of inversion of biodegradation level of oil columns, biodegradation level is mainly controlled by the vertical distance from its in situ place to OWC, which is characterized by the biodegradation degree increasing from the top of oil columns to the bottom with excellent gradient variations. Laterally, the biodegradation level varies significantly within the reservoir. It is mainly dominated by the extent of oil-water-contact area controlled by intercalations. And intercalations also lead to the insufficient supply of nutrients and poor metabolism exchange because the fluid flow can hardly pass in the area where intercalations develop, which results in lower biodegradation. A model of control effects of petroleum biodegradation degree by bottom water and reservoir heterogeneity within the oil reservoir is established, and its application in heavy oil reservoir development is discussed in this paper. © 2015, Editorial Department of Earth Science-Journal of China University of Geosciences. All right reserved.