In Qintong sag

low-mature oil occur in several wells and intervals

including the Ed

1

of Yin 2 well and the Et

1

of Su 168 well in Yinzhuang oilfield located in the outer slope zone

the Ef

<

sub

>

<

sub

>

3 of Su 168 well in Mao-shan oilfield located in the fault horst zone

and the Ed

1

of Su 228 well in Jiaodunzi oilfield and the Es

1

of Su 120 well in Caoshe oilfield located in the fault bench zone.The low-mature oil are characterized by high wax content

low sulfur content

low kinematic viscosity and large variation of density.The values of ααα C

29

sterane's 20S/(20S+20R) and C

29

sterane's αββ/(ααα+αββ)

the diagnostic indexes for low-mature oil in this sag

are 0.31 and 0.29

respectively.The biomarkers sterane isomerization parameters

ααα C

29

sterane's 20S/(20S+20R) is in the range of 0.23-0.29 and C

29

sterane's αββ/(ααα+αββ)is in the range of 0.24-0.28;the content of rearranged sterane is very low.At the same time

several unstable biomarkers

including 5β(H)-coprostane

carotane l and dehydroxyl vitamin-E families

are also detected.The observations that the source rocks were deposited in mildly brackish to brackish water and the low maturity of source rocks are well evidenced by the relatively low gammacerane/C

30

hopane ratio

sulfur content less than 0.5% and the existence of C

30

～C

31

lanostane in tetracyclic triterpane.