Baimiao field

located in the southern part of Dongpu depression

is mainly a condensate gas field

with oil ring at the bottom.The study of biomarkers indicates that the oil in different parts of the structures might be derived from various source rocks.The crude oil in deeper positon (bottom and flank) has been originated from the 2nd submember source rock of 3rd member

Shahejie Fm (Es

3

2

)

and that in the higher part of the structure top has been originated from the Es

3

3

Es

3

4

and even Es

4

source rocks.The former

in comparison to the latter

is characterized by relatively abundant oleanane

gammacerane

C

30

diahopane and C

29

Ts

high values of Ts/Tm and diasterane/regular steranes ratios

and high C

29

ββ/(αα+ββ)and 20S/(R+S) indexes of C

29

steranes. The low values of C

29

ββ/(αα+ββ)and 20S/(R+S)of C

29

steranes indicate the source rocks of Es

3

3

and Es

3

4

submembers might generate hydrocarbons at early maturation stage.