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AAPG Bulletin, Preliminary version published online Ahead of Print 15 November 2025.

Copyright © 2025. The American Association of Petroleum Geologists. All rights reserved.

DOI:10.1306/11122524007

Sedimentary evolution and shale oil potential of Shahejie Formation in Zhanhua Sag, Bohai Bay Basin, China

Shang Xu1 , Yufan Wang1 , Fang Hao1 , Huimin Liu2 , Yuanyin Zhang3 , Bo Gao4 , Kelai Xi1 , and Qiqi Li5

1 State Key Laboratory of Deep Oil and gas, China University of Petroleum (East China), Qingdao, 266580, P. R. China
2 Shengli Oilfield Branch Company, Sinopec, Dongying, 257015, China
3 Institute of Energy, Peking University, 100871, China
4 Binnan Oil Production Plant, Shengli Oilfield Branch, Sinopec, Binzhou, 256606, China
5 Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education, China University of Mining and Technology, Xuzhou, 221116, China

Ahead of Print Abstract

It is important to accurately classify shale lithofacies and identify their origin and hydrocarbon content for both shale oil and gas reservoirs. Oil-bearing lacustrine shales (average TOC content=3.12 wt%, average Ro=0.81%) of the lower third member (Es3L) of the Eocene Shahejie Formation in the Zhanhua Sag, Bohai Bay Basin contain eight lithofacies that are differentiated based on mineralogy, total organic carbon content (TOC), grayscale, elemental composition and Rock-Eval pyrolysis data. The results show that four lithofacies are most common: moderately organic-rich laminated calcareous shale, organic-rich laminated calcareous shale, and organic-rich calcareous/massive mixed shale. Paleoenvironment controls lithofacies evolution. Unit 1 (arid): Limited detrital/nutrient inflow and low water energy, coupled with transgression-induced high salinity suppressed freshwater bioproductivity, favoring moderately-enriched laminated calcareous shale. Unit 2 (transition): Increased productivity promoted organic-rich laminated calcareous shale. Unit 3 (humid): Nutrient and detrital input (TOC undiluted) in the lake increases; however, the destruction of the quiet water environment leads to the gradual disappearance of laminae, shifting lithofacies to organic-rich massive calcareous and organic-rich massive mixed shales, moderately-enriched laminated calcareous shale, organic-rich massive calcareous shale, and organic-rich massive mixed shale that have high shale oil potential. Two high-brittleness and high-oil sweet-spot intervals were identified (2988 m~3012 m and 3108 m~3124 m in well A): interval 2 is enriched in situ hydrocarbon via high TOC and large storage; interval 1, despite lower TOC, accumulated migrated hydrocarbons via micromigration and large reservoir space.

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Please cite this AAPG Bulletin Ahead of Print article as:

Shang Xu , Yufan Wang , Fang Hao , Huimin Liu , Yuanyin Zhang , Bo Gao , Kelai Xi , Qiqi Li: Sedimentary evolution and shale oil potential of Shahejie Formation in Zhanhua Sag, Bohai Bay Basin, China, (in press; preliminary version published online Ahead of Print 15 November 2025: AAPG Bulletin, DOI:10.1306/11122524007.

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