Reservoir Evaluation and Development ›› 2022, Vol. 12 ›› Issue (1): 233-245.doi: 10.13809/j.cnki.cn32-1825/te.2022.01.020

• Shale Oil • Previous Articles     Next Articles

Description and its hydrocarbon geological implications of outcrop sections of Triassic Chang-7 Member in southern Ordos Basin

ZHAO Junfeng1(),LIU Chiyang1,ZHANG Dongdong1,GUO Yixuan2,QI Yalin2,LYU Qiqi3,ZHANG Long1,4,MA Huanhuan1,5   

  1. 1. State Key Laboratory of Continental Dynamics/Department of Geology, Northwest University, Xi’an, Shaanxi 710069, China
    2. Exploration and Development Research Institute, Changqing Oilfield Company of PetroChina, Xi’an, Shaanxi 710018, China
    3. School of Geoscience, Yangtze University, Wuhan, Hubei 430100, China
    4. School of Earth Science and Engineering, Xi’an Shiyou University, Xi’an, Shaanxi 710065, China
    5. Changqing Geophysical Prospecting Section, BGP INC., China National Petroleum Corporation, Xi’an, Shaanxi 710200, China
  • Received:2021-05-31 Online:2022-02-26 Published:2022-03-24

Abstract:

Chang-7 Member in the Triassic Yanchang Formation served as the most important source rock of oil in the Mesozoic Ordos Basin, and it is also the realistic interval for the exploration and development of shale oil. The Chang-7 Member represents the climax depositional period of the Triassic lake basin. It is composed of a set of fine-grained clastic rocks, including mudstone and oil shale etc. The thickness of the Chang-7 Member is 100~120 m, which can be divided into three sub-members. Among them, the Chang-71 and Chang-72 sub-members have been proved as the key intervals for exploration and development of shale oil. To deepen the understanding of the sedimentary environment and oil and gas geological characteristics of the Chang-7 Member, measurement of the field sections are combined with the previous work. The well-exposed sections of the Chang-7 Member in Yishicun, Beiyincun, Yaoqu, Bawangzhuang and Tangnihe in Tongchuan area are described in detail. Furthermore, the geological background of the formation of hydrocarbon-rich depression in the middle-late Triassic stages is discussed. Our results show, the lake basin went through gradual shrinkage and declining lake level from Chang-73 sub-member to Chang-71 sub-member, and the sandstone content gradually increase to the upper part. The study area is located in the deep lake area of the Yanchang Formation deposition. The sedimentary types in the Chang-7 Member include not only normal deep-water fine-grained sedimentary rocks, but also diverse deep-water gravity flow deposits, volcanic tuff, and carbonate rocks which might source from hydrothermal fluid in the deep part. These important phenomena record the special process of the formation of the hydrocarbon-rich depression, and have important implications for understanding the hydrocarbon formation and enrichment mechanism, as well as the exploration and development of shale oil.

Key words: outcrop section, shale oil, hydrocarbon-rich depression, Chang-7 Member, Yangchang Formation, Ordos Basin

CLC Number: 

  • TE121