Oil & Gas Geology ›› 2019, Vol. 40 ›› Issue (6): 1259-1269.doi: 10.11743/ogg20190610

• Petroleum Geology • Previous Articles     Next Articles

Mechanism of shale oil accumulation in the Hetaoyuan Formation from the Biyang Depression,Nanxiang Basin

He Taohua1,2, Li Wenhao1,2, Tan Zhaozhao3,4, Wang Ya1,2, Zhang Wenbo1,2, Zhang Xinwen5   

  1. 1. Key Laboratory of Deep Oil and Gas, China University of Petroleum(East China), Qingdao, Shandong 266580, China;
    2. School of Geosciences, China University of Petroleum(East China), Qingdao, Shandong 266580, China;
    3. State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangdong, Guangzhou 510640, China;
    4. University of Chinese Academy of Sciences, Beijing 100049, China;
    5. Research Institute of Exploration and Development, Henan Oilfield Company, SINOPEC, Zhengzhou, Henan 450000, China
  • Received:2018-11-25 Revised:2019-02-27 Online:2019-12-28 Published:2019-10-15

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Abstract: The continental shale oil potential is remarkably huge in China,but the current production of shale oil is much less than expected.Therefore,in order to reveal the geochemical characteristics and shale oil accumulation mechanism of organic-rich shales,a multiple geochemical techniques,mainly including total organic carbon (TOC),Rock-Eval,organic maceral and gas chromatography mass spectrometry (GC-MS),were systematically performed on a total of 50 shale samples from shale oil field in the Biyang Depression,Nanxiang Basin,in this study.On the basis of the diversities in the color,structure and microscopic characteristics,two types of shales have been identified,which are black laminated shale (type A) and gray shale (type B,including gray shale,dark mudstone and few silty mudstones),respectively.The testing results show that (1) type A,mainly formed in high salinity and strong reducing environment,is rich in TOC (up to 8.59%) and algea organic matter (AOM) with kerogen of type Ⅰ,and contains plenty of the horizontal cracks favorable for shale oil storage which have enhanced the abundant oil content (high free hydrocarbon S1 and chloroform bitumen "A" concentrations) at present,resulting that the enriched shale oil resources occurred in this type of shales;(2) type B,mainly developed in weak reduction environment with low salinity,has less TOC abundance (low to 1.09%) with kerogen of type Ⅱ and poor AOM contribution,and vertical cracks within shales have accelerated the hydrocarbon expulsion,which has led to today's poor oil content and resulted that this type of shales only contains potential and ineffective shale oil resources.Thus,the type A of shales can effectively generate and store abundant shale oil,which is of great reference value for further exploration and development of shale oil in the future.

Key words: algea organic matter, salinity, redox environment, shale oil resource, organic-rich shale, Biyang Depression

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