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| Organic lithofacies and its reservoir characteristics of lacustrine shales of the Dongyuemiao Member in the Jurassic Ziliujing Formation, eastern Sichuan Basin |
| Ming—Yang Weia,b, Wang Chena,b,*, Xing—Zhi Wanga,b, Zhi—Dong Baoc, De—Ming Zenga,b, Jia—Hao Kanga,b, Yang Lia,b, Kai—Ming Liua,b, Fei Huoa,b |
aState Key Laboratory of Reservoir Geology and Development Engineering, Southwest Petroleum University, Chengdu 610500, Sichuan Province, China;
bSchool of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, Sichuan Province, China;
cState Key Laboratory of Petroleum Resource and Prospecting, China University of Petroleum (Beijing), Beijing 102249, China |
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Abstract This study investigates the reservoir properties and main controlling factors of different organic lithofacies in the Jurassic Dongyuemiao Formation lacustrine shales, eastern Sichuan Basin. Based on lithofacies classification, the spatial characteristics and physical properties of the reservoirs, along with the primary controlling factors, were analyzed using core observation, scanning electron microscopy (SEM), low—temperature nitrogen adsorption, and other techniques. The results indicate that: 1) In the eastern Sichuan Basin, the Dongyuemiao Member is predominantly composed of clay minerals and quartz, which are the main mineral constituents of the lacustrine shales. Minor amounts of calcite, feldspar, dolomite, pyrite, and rhodochrosite are also present. Four main lithofacies were identified within the study area: argillaceous shale with high—medium TOC (Ⅰ2), mixed shale with low—medium TOC (Ⅱ1), argillaceous—silt mixed shale with medium—low TOC (Ⅱ2), and argillaceous siltstone with low TOC (Ⅲ2). 2) The shale microstructure is characterized by micropores, primarily comprising intergranular pores between clay minerals and organic—matter pores. Intragranular dissolution pores, notably within shell fragments, are locally developed. Microfractures are mainly observed as intra—layer shale fractures and fractures along the edges of shell fragments. 3) High organic matter abundance (>1%), high clay mineral content (>40%), and moderate carbonate mineral content (<10%) in the shale of the study area contribute to the development of pores. In contrast, high quartz and feldspar mineral content (>50%) and excessively high (>12%) or low (<8%) carbonate mineral content inhibit shale pore development. 4) A comprehensive analysis shows that the argillaceous—silt mixed shale with medium—low TOC (Ⅱ2) is the most favorable lithofacies for reservoir development, followed by argillaceous shale with high—medium TOC (Ⅰ2). The mixed shale with lower—medium TOC (Ⅱ1) is less favorable, and the argillaceous siltstone with low TOC (Ⅲ2) is the poorest. Considering the vertical distribution of lithofacies in the Dongyuemiao Member, it is concluded that the middle—upper part of the Dong 2 submember is the most prospective reservoir interval in the study area.
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Received: 30 July 2024
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Corresponding Authors:
*State Key Laboratory of Reservoir Geology and Development Engineering, Southwest Petroleum University, Chengdu 610500, Sichuan Province, China. E—mail address: chenwang0208@163.com (W. Chen).
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2026, Vol. 15 
