Organic geochemical characteristics of Eocene crude oils from Zhanhua Depression, Bohai Bay Basin, China
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ORIGINAL ARTICLE
Organic geochemical characteristics of Eocene crude oils from Zhanhua Depression, Bohai Bay Basin, China Yujiao Zhang1,2 • Hong Lu1 • Yao-Ping Wang3 • Xin Zhan4 • Ping’an Peng1
Received: 26 November 2019 / Revised: 16 March 2020 / Accepted: 24 March 2020 Ó Science Press and Institute of Geochemistry, CAS and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Geochemical studies of crude oil and source rock play an important role in future exploration in Zhanhua Depression. In this study, thirty-one oil samples collected from Shahejie Formation in Zhanhua Depression, Bohai Bay Basin, NE China have been geochemically analyzed and their organic geochemical characteristics have been applied to differentiate groups of oils. These oil samples can be classified into two families based on multiple biomarker proxies and stable carbon isotopic values. Family I is characterized by a low ratio of pristane over phytane (Pr/Ph \ 0.7), a relatively high ratio of phytane over n-C18 (Ph/n-C18), varying ratios of gammacerane over C30 hopane (Ga/C30H) and C22/C21 tricyclic terpane, and a low ratio of C19/C23 tricyclic terpane. Family II is marked by a relatively high Pr/Ph ratio (0.7–1.6), relative low ratios of Ph/n-C18 and C22/C21 tricyclic terpane, and avarying ratio of C19/C23 tricyclic terpane. Both families I and II within these crude oils can be subdivided into two families based on different values of stable carbon isotopic composition of individual n-alkanes. Moreover, the potential source rocks of oil samples in Family I and Family II were likely derived from the upper Es4 member
& Hong Lu [email protected] 1
State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academic of Sciences, Guangzhou 510640, China
2
University of the Chinese Academy of Sciences, Beijing 100049, China
3
College of Chemistry and Environmental Science, Guangdong Ocean University, Zhanjiang 524088, China
4
Geology and Geophysics Program, Missouri University of Science and Technology, Rolla, MO 65409, USA
and Es3 member, respectively, based on the correlation of organic geochemical characteristics of the oils and source rocks. The results of oil–source rock correlation provide insight into the process from oil generation to migration and to final accumulation, providing a better understanding of factors controlling oil–gas distribution for prediction of sweet spots. Keywords Zhanhua depression Bohai Bay Basin Biomarkers Stable carbon isotopic compositions Crude oil
1 Introduction A key problem in the oil–source study is to distinguish the effects of source on oil compositions, including organic matter input, depositional environment, and thermal maturity (Peters et al. 2005). Biomarkers are widely used in identifying groups of genetically related oils and correlating oils with source rocks (Moldowan et al. 1985; Peters et al. 2005). Their distributions and parameters can be used to interpret the depositional conditions and describe the source rock of migrated oil
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