Abstract:

Research on deltas in Qibei sag can be done on different scales.After the works of the application of seismic attributes, the tracing of seismic facies and the analysis of the sand distributed system,we find that the composite delta is divided into western part and migratory eastern part. The seismic facies present that there is a similar “s”-type foreset reflectance characteristics of the delta of the second member of Shahejie Fomation in Qibei sag, which is seismic reflection characteristics of lateral migration of delta.Based on the discovery of the phenomenon of lateral migration, we track the axes in seismic profiles in plane to determine the scope of the the migratory delta in plane of each period of time, finally acquire the area and evolution of the delta with all the periods of time,and find that in the lowstand systems tract of the second member of Shahejie Fomation the East Delta migrate eastwardly six times while in the highstand systems tract the East Delta migrate eastwardly four times.The West Delta continually deposits vertically. The existence of the phenomenon of lateral migration makes the East Delta has different heterogeneity characteristics from others, sandstone possess interaction of positive rhythm and counter-rhythm. Porosity which as a whole is relatively low with an average 14% in East Pelta, is lower than the average of  24.4% in the West Delta; the average sediment permeability of this type, which is 0.0172×10^-3 μm², is lower than that of the West Delta which is 0.0375 × 10^-3 μm²; content of carbonatite with an average of 13.5% in East Delta, is higher than that with the average of 9.6% in the West delta.

Key words:  , complex delta；inner structure；the second member of Shahejie Formation；Qibei sag