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 diffe

rentiation 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.