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Polished Version - Reservoir Characteristics of Fine-Grained Rocks in the Du-3 Submember of the Fourth Member of the Shahejie Formation, Western Sag of the Liaohe Depression

Yang Li¹², Cang Chen¹, Xiaolong Zhou¹, Youlin Huang³

Environment and Resource / 2026,8(2): --- / 2026-06-24 22 19

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• Information:

  1. Liaohe Oilfield, CNPC, Panjin, Liaoning;
  2. College of Petroleum Engineering, Liaoning Petrochemical University, Fushun, Liaoning;
  3. Research Institute of Exploration and Development, Qinghai Oilfield, CNPC, Dunhuang, Gansu

• Keywords:
  Western sag; Fine-grained sedimentary rocks; Unsupervised learning; Overlapping probability; Reservoir evaluation
• Abstract: Lacustrine fine-grained sedimentary rocks comprising mixed clay minerals, felsic minerals, carbonates, and analcime were deposited in the Du-3 Submember of Member 4 of the Shahejie Formation in the Leijia area, Western Sag, Liaohe Depression. These rocks have become key targets for tight-oil and shaleoil exploration in recent years. Building upon previous studies, this work integrates drilling, wireline logging, mud logging, and laboratory analytical data, and incorporates an unsupervised learning approach to: (1) classify fine-grained rocks in the target interval, (2) characterize fundamental reservoir geological attributes, (3) evaluate reservoir quality, and (4) predict favorable zones. K-means clustering was performed on 303 sets of quantitative whole-rock X-ray diffraction (XRD) data, classifying the Du-3 lithologies into three types: carbonate rocks, felsic mixed fine-grained rocks, and analcime-rich mixed fine-grained rocks. Among these, carbonate rocks and analcime-rich mixed fine-grained rocks exhibit higher brittleness and are thus to fracturing. Dissolution pores and vugs preferentially develop along fractures, resulting in improved storage and seepage capacity. Overall, the Du-3 reservoirs are characterized by small pore–throat radii, poor sorting, low homogeneity coefficients, and an unfavorable pore structure. The development of effective reservoirs relies primarily on micropores and microfractures. Using an overlapping probability evaluation method, six key factors controlling reservoir development—brittleness index, carbonate thickness, fracture density, average porosity, average permeability, and total organic carbon (TOC)—were integrated for reservoir assessment. Favorable reservoir zones are mainly distributed along the long axis of the lacustrine basin, including the L15–L84–L59–S90–L93 well areas.
• DOI: 10.35534/er.08020xx (registering DOI)
• Cite: Li, Y., Chen, C., Zhou, X. L., Huang, Y. L. (2026). Polished Version - Reservoir Characteristics of Fine-Grained Rocks in the Du-3 Submember of the Fourth Member of the Shahejie Formation, Western Sag of the Liaohe Depression. Environment and Resource, 8(2),