Lithofacies characteristics and sweet spot distribution of lacustrine shale oil; a case study from the Dongying Depression, Bohai Bay Basin, China

• Published in: Lithosphere Vol. 2022; no. Special 12
• Main Authors: Ma Pengjie, Ma Pengjie, Lin Chengyan, Lin Chengyan, Li Guiang, Li Guiang, Dong Chunmei, Dong Chunmei, Jiang Long, Jiang Long, Du Xinyu, Du Xinyu, Ren Minhua, Ren Minhua, Liu Weibin, Liu Weibin, Zhao Ziru, Zhao Ziru, Yuan Yue, Yuan Yue, Lang Kaihao, Lang Kaihao
• Format: Journal Article
• Language: English
• Published: GeoScienceWorld 2022
• Subjects: Asia; Bohaiwan Basin; case studies; Cenozoic; China; clastic rocks; cores; Dongying Depression; Economic geology; energy sources; Far East; geochemistry; lacustrine environment; lithofacies; petrography; petroleum; petroleum engineering; petroleum exploration; reservoir rocks; rock mechanics; sedimentary rocks; Shahejie Formation; shale; shale oil; Shandong China; Tertiary; thin sections; unconventional reservoirs; X-ray diffraction data
• ISSN: 1941-8264; 1947-4253
• DOI: 10.2113/2022/3135681

Lacustrine shale is characterized by rapid lithofacies transformation and compositional heterogeneity, which present challenges in shale oil sweet spot evaluation and distribution prediction and should be systematically studied. Field emission-scanning electron microscopy (FE-SEM), low-pressure adsorption isotherm analysis, mercury intrusion porosimetry (MIP), and triaxial compression testing were employed to comprehensively analyze the oil-bearing capacity, reservoir properties, fluidity, and frackability of different lithofacies. Via analyses of mineral composition, total organic carbon (TOC) content, and sedimentary structure, seven lithofacies were identified: organic-rich calcareous shale (L1), organic-rich laminated calcareous mudstone (L2), organic-rich laminated carbonate-bearing mudstone (L3), intermediate-organic laminated calcareous mudstone (L4), organic-poor laminated calcareous mudstone (L5), organic-poor thin-bedded calcareous mudstone (L6), and organic-rich laminated silty mudstone (L7). Considered together, the oil-bearing capacity, reservoir properties, fluidity, and frackability suggested that the L1 and L7 lithofacies were high-quality sweet spots, with satisfactory oil-bearing capacity (TOC>3.5%; S1>10 mgHC/grock), well-developed pores and microfractures, notable fluidity (as indicated by a high oil saturation index value), and suitable brittleness. The sweet spot distribution was predicted according to multiresolution graph-based clustering analysis of well logs. The results indicate that comprehensive research of the key factors for shale oil and lithofacies prediction can promote sweet spot prediction and enhance shale oil exploration.