Abstract:

According to the classical theories of the oil and gas accumulation, oil and gas are always gathering in the trap of high position. However, the phenomenon of OWC differentiation occurrs occasionally during the actual exploration and development of the oil field. W oilfield located in the concave inversion zone of the middle section in Liaozhong sag of Bohai Sea is a complex fault block reservoir. For the developed wells in the strike slip zone of the oilfield, we analyze the causes of the OWC differentiation. On the basis of the stratification and contrast, the reasons are mainly from the aspects of structure, accumulation and reservoir. It shows that OWC differentiation is due to the poor accumulation condition and sand body superimposition. According to the research on tracking of sand body and deposition characterization, it is considered that Dong-3 segment of this area shows the retrogradation phenomena, while the Dong-2 segment shows the progradation phenomenon. Besides, the Dong-2 segment's sand strata ratio is higher than that of Dong-3 segment. The mudstone of Dong-3 segment is relatively developed with good longitudinal plugging. Meanwhile, the progradation and retrogradation patterns are corresponding to the superposition relation of different sandbody. Then, a difference in oil-water interface appeared.

Key words: Bohai, complex faulted block, strike slip zone, OWC differentiation, sandbody superimposition