New cognition on stratigraphic structure of Yanchang Formation and discussion on enrichment model of shale oil in Ningxian—Zhengning area, southern Ordos Basin

doi:10.3969/j.issn.1672-7703.2024.05.008

Abstract

Abstract: Ordos Basin is rich in shale oil resource with different level of exploration and cognition basin-wide, and stratigraphic structure of Yanchang formation, forming and controlling factors on enrichment for shale oil need to be deepened.The stratigraphic structure of Yanchang Formation is re-established, and the controlling factors on formation and enrichment are discussed for shale oil of Member Chang7 through the full application of newly acquired high-density and wide-azimuth 3D seismic data, combining drilling logging and analytical data in Ningxian-Zhengning area, southern Yishan Slope belt. The latest comprehensive study show that Member Chang 7 to Chang2 of Yanchang formation has the stratigraphic structure of wedge-shaped development and progradation layer by layer towards the lacustrine center, the provenance of Yanchang formation is mainly from the Qinling Orogenic Belt for Ningxian-Zhengning area, and sedimentary sequence of single-stage wedgeshaped formation is filled with fluvial-delta, semi-deep lake, deep-lake gravity-flow deposits along the sediment-supply direction, which has the characteristics of “same period with different sedimentary facies”. Deposits of sandy debris flow and turbidity flow are developed in Member Chang7 mainly, which belong to low-porosity and ultra-low porosity ultra-low permeability tight reservoir generally with characteristics of rapid lateral change and strong reservoir heterogeneity. The low-permeability, tight oil and shale oil reservoirs are continuously developed encompassing the main source rock of chang 7, resulting in three reservoir combination types including reservoir below source rock, reservoir and source rock co-existing in same layer, reservoir above source rock in Yanchang Formation. intercalated shale oil mainly exists in Chang7, controlled by combination of high-quality source rock, advantageous microfacies, fractures and structure. High-quality source rock controls beneficial distribution range of shale oil,sedimentary facies and fractures control enrichment area.

Key words: Ordos Basin, Ningxian-Zhengning area, Yanchang Formation, stratigraphic structure, Member Chang 7, shale oil, controlling factor, enrichment model

CLC Number:

TE112.1

Hu Yingjie, Li Xiaoguang, Shan Junfeng, Liu Xingzhou, Gu Tuan, Ju Juncheng, Mou Chun, Wang Yusi. New cognition on stratigraphic structure of Yanchang Formation and discussion on enrichment model of shale oil in Ningxian—Zhengning area, southern Ordos Basin[J]. China Petroleum Exploration, 2024, 29(5): 91-105.

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