DIVIDING SYSTEM TRACTS WITH VARIOUS GEOLOGICAL DATA ON DIFFERENT SCALES ——TAKING THE SECOND MEMBER OF DONGYING FORMATION IN THE SOUTHEAST OF SHALEITIAN UPLIFT OF BOHAI AREA AS AN EXAMPLE

There are significant differences in the sandstone distribution and oil-gas accumulation character in different system tract. The correct division of system tract is of significance for petroleum exploration, particularly exploration of subtle traps. Comparing to marine strata, the division of continental sequence system tracts is difficult because due to its complexity. Different scholars advocate different division schemes, and we are difficult to make sure the position of system tract boundaries. Taking the division of the system tracts for the second Member of the Dongying Formation in the southeast of Shaleitian uplift of the Bohai area, this paper puts forward the method using variety of geological data on different scales to distinguish lowstand system tracts, transgressive system tracts and highstand system tracts from each other. This method can help us escaping from the mistakes often encountered in the analysis of well data directly and better use the relative lake-level change curve, as a solid step to establish the standard of sequence division for Dongying Formation. As the depositional characteristics, types of traps and reservoir characteristics are quite different in different systems tract, the correct division of the system tract is significance for the hydrocarbon exploration.