Main Controlling Factors and Favorable Exploration Direction of Shale Oil Enrichment in Chang 7 Member of Ordos Basin

Key words: 
• shale oil /
• lithologic combination /
• main controlling factors /
• exploration direction /
• Chang 7 member /
• ordos Basin

Abstract: Abstract: [Objective] The main controlling factors and exploration potential of different types of shale oil enrichment in the Chang 7 member of the Ordos Basin are discussed, and the next exploration direction is identified. [Methods] In this study, the formation conditions and exploration potential of shale oil such as petrology, geochemical characteristics and reservoir capacity of the Chang 7 shale were comprehensively studied using organic geochemistry, whole rock X-ray diffraction (XRD), field emission scanning electron microscopy, and rock pyrolysis experiments. [Results] The results show that: (1) The Chang 73 shale has high organic matter abundance, the best type, the highest maturity, and the greatest hydrocarbon generation potential. (2) The Chang 7 shale is dominated by inorganic pores and fractures, with the largest proportion of micropores, and the shale reservoir capacity is stronger than that of mudstone. (3) The enrichment of shale oil in the Chang 7 member is controlled by five factors : high-quality source rock, lithologic combination, fracture, mobility, and fracability. The distribution of high-quality source rocks controls the distribution range of shale oil, and the lithology combination controls the hydrocarbon expulsion efficiency and the enrichment type of shale oil. The hydrocarbon expulsion efficiency of the source-reservoir interbedded type is the highest, which is conducive to the enrichment of sand bodies; the hydrocarbon expulsion efficiency of the thick source-thin reservoir type is the lowest, which is conducive to the in-situ retention and enrichment of shale oil. The two-sidedness of fractures controls the enrichment degree of shale oil. The development of fractures is conducive to the enrichment of sandstone interlayer shale oil, and the underdevelopment of fractures is conducive to the retention and enrichment of pure shale-type shale oil. The mobility and fracability of crude oil control the high yield of shale, and the mobility and brittleness index of shale crude oil are better than those of mudstone. [Conclusion] The Chang 73 sub-member in the Jiyuan area is a favorable exploration block for pure shale-type shale oil. The Zhengning and Northern Shaanxi areas are favorable exploration blocks for sandstone-intercalated shale oil in the Chang 71 and Chang 72 sub-members. The Huachi area in Longdong is a favorable area for the exploration of both sandstone-intercalated and pure shale-type shale oil.