Oil & Gas Geology ›› 2005, Vol. 26 ›› Issue (4): 512-517.doi: 10.11743/ogg20050419

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Biomarker features of low-mature oil in Qintong sag and maturity analysis

Hu Ying, Zhang Zhihuan, Fang Chaohe   

  1. Key Laboratory for Hydrocarbon Accumulation, Ministry of Education, Beijing
  • Received:2005-08-09 Online:2005-08-25 Published:2012-01-16

Abstract:

In Qintong sag,low-mature oil occur in several wells and intervals,including the Ed1 of Yin 2 well and the Et1 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 Ed1 of Su 228 well in Jiaodunzi oilfield and the Es1 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 C29 sterane's 20S/(20S+20R) and C29 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 C29 sterane's 20S/(20S+20R) is in the range of 0.23-0.29 and C29 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/C30 hopane ratio,sulfur content less than 0.5% and the existence of C30~C31 lanostane in tetracyclic triterpane.

Key words: Qintong sag, low-mature oil, lanostane, isomerization parameter

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