Based on the analysis of index correlativity

the lower limit of hydrocarbon expulsion indexes(R

o

≥0.6%

SM≥0.10

C

29

Mor/C

29

Hop≤0.45

and CPI≤1.3)are selected through the study of shows at various levels.The indexes are used as the threshold values of hydrocarbon expulsion from source rocks in the Paleogene and Taizhou Formation in Subei basin to define the expulsion range of each set of source rocks.In Jinhu sag

the source rocks capable of expulsion in the fourth Member of Funing Formation are mainly distributed inSanhe

Longgang

and Chaxi sub-sags;and that in the second Member pf Funing Formation are also mainly located in the above-mentioned three sub-sags and their inner slopes.While in Gaoyou sag

source rocks capable of expulsion in the fourth Member of Funing Formation are mainly limited within the deep o fGaoyou sag

Liulushe subsag

and the inner slope

and that in the second Member of Funing Formation are extensively distributed in all areas but the Zheduo swell.Methods such as fluorescence thin section

hydrocarbon inclusion analysis

and oilsource correlation and tracing are employed to explore the oil and gas migration boundary in the basin.According to the research

hydrocarbons from Gaoyou and Linze sags have accumulated in Zheduo swell after a long distance migration.The analysis shows that the oil in Taizhou Formation in Well XC 1 might come from the Linze sag.The phenomenon that hydrocarbons generated by the upper source rocks accumulate in the lower reservoirs is largely the result of consequent normal fault adjustment; while the oil in the first Member of Funing Formation in Well XC1 might come from the mature source rocks in the Taizhou Formation in eastern Gaoyou sag after a long distance migration(about 20 km)resulted from antithetic normal fault adjustment(hydrocarbons generated from the lower source rocks accumualate in the upper reservoirs).