Natural Resources Research

, Volume 28, Issue 1, pp 241–257 | Cite as

Deep-Lacustrine Shale Heterogeneity and Its Impact on Hydrocarbon Generation, Expulsion, and Retention: A Case Study from the Upper Triassic Yanchang Formation, Ordos Basin, China

  • Bojiang FanEmail author
  • Liang Shi
Original Paper


The Chang-7 shale of the Upper Triassic Yanchang Formation was deposited in a deep-lacustrine environment in the southwest part of the Ordos Basin. It is characterized by a strong lithological heterogeneity, consisting primarily of pure shale and sandy laminated shale. This study explored the impact of sandy laminae in the thick pure shale on hydrocarbon generation, retention, and expulsion, which were rarely considered in previous studies. Based on core observation, thin section, and geochemical analysis, the hydrocarbon generation, retention, and expulsion characteristics were obtained for both pure shale and sandy laminated shale. In general, the Chang-7 shale stays at low mature to mature thermal evolution stage and has good hydrocarbon generation potential. It contains mainly Type II kerogen with an average total organic carbon (TOC) of 2.9% and average (S1 + S2) of 8.2 mg/g. Compared with sandy laminated shale, pure shale contains more retained liquid hydrocarbon and has a higher amount of asphaltene and nitrogen–sulfur–oxygen (NSO) polarized components, indicating a relatively weak hydrocarbon expulsion process. The middle part of a thick pure shale retains more liquid hydrocarbon and has higher percentages of asphaltene and NSO polarized components than that of the top and basal part of the shale where sandy laminae occur. The difference in hydrocarbon retention capacity is interpreted to have been primarily caused by the comparatively higher reservoir quality of the sandy laminated shale, having higher amount of brittle minerals and larger pores than the pure shale. Polymer dissolution and nanopore adsorption are also key factors in hydrocarbon retention and component partition. Based on this study, we suggest that sandy laminated shale, which receives most of the hydrocarbon from adjacent pure shale, should be the current favorable shale oil exploration targets. Even though pure shale contains high hydrocarbon potential, its development is still pending improved technologies, which could solve the challenges caused by complicated geological conditions.


Sandy laminae Shale heterogeneity Oil retention Yanchang Formation Ordos Basin 



This paper is financially supported by China National Natural Science Foundation Program, Grant No.: 41702136. The authors wish to acknowledge Shaanxi Yanchang Petroleum (Group) CO., LTD., for providing samples.


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Copyright information

© International Association for Mathematical Geosciences 2018

Authors and Affiliations

  1. 1.School of Petroleum and Environmental EngineeringYan An UniversityYan AnChina

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