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<p>Technological innovations in hydrocarbon exploration and development have advanced significantly over recent decades. However, effective methods for fluid identification in fine-grained sediments remain limited. The reduced sensitivity of well logs to movable fluids in fine-grained sandstones hampers fluid identification and undermines the utility of conventional crossplot techniques. To address this issue, we conducted a case study on the Es<sub>2</sub> Member of the Shahejie Formation in the Bohai Bay Basin. Petrographic analysis and porosity and permeability measurements were performed on core samples from the study area. Additionally, conventional well logs and production test data from drill stem testing were analyzed. The sandstones were found to be predominantly silt-sized lithic arkoses with low porosity (2.2–21.4%, average 12.7%) and low permeability [0.02–34.1 mD (1 mD (millidarcy) = 9.869233 × 10<sup>−16</sup> m<sup>2</sup>.), average 2.27 mD]. Oil-bearing layers generally exhibited higher resistivity than water-bearing layers, and some oil-bearing intervals showed resistivity values as low as 6.6&#xa0;Ω·m, overlapping with water-bearing layers that exhibited resistivity up to 30&#xa0;Ω·m. This anomaly is primarily attributed to the combined effects of burial depth, fine-grained sediment content, and porosity on resistivity logging responses. To compensate these influences and enhance fluid discrimination, we propose the apparent resistivity index (ARI) as a novel method for fluid type identification. Application of the ARI successfully differentiated fluid types, demonstrating its potential as an effective method for fluid identification in fine-grained sandstones.</p>

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An Identification Method of Low-Contrast Pay for Fine-Grained Sediment Reservoirs

  • 期刊论文

  • 发表日期：

    2026年1月3日

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  • Xuqiang Fan,
  • Yufeng Cui,
  • Guiwen Wang

摘要

Technological innovations in hydrocarbon exploration and development have advanced significantly over recent decades. However, effective methods for fluid identification in fine-grained sediments remain limited. The reduced sensitivity of well logs to movable fluids in fine-grained sandstones hampers fluid identification and undermines the utility of conventional crossplot techniques. To address this issue, we conducted a case study on the Es2 Member of the Shahejie Formation in the Bohai Bay Basin. Petrographic analysis and porosity and permeability measurements were performed on core samples from the study area. Additionally, conventional well logs and production test data from drill stem testing were analyzed. The sandstones were found to be predominantly silt-sized lithic arkoses with low porosity (2.2–21.4%, average 12.7%) and low permeability [0.02–34.1 mD (1 mD (millidarcy) = 9.869233 × 10−16 m2.), average 2.27 mD]. Oil-bearing layers generally exhibited higher resistivity than water-bearing layers, and some oil-bearing intervals showed resistivity values as low as 6.6 Ω·m, overlapping with water-bearing layers that exhibited resistivity up to 30 Ω·m. This anomaly is primarily attributed to the combined effects of burial depth, fine-grained sediment content, and porosity on resistivity logging responses. To compensate these influences and enhance fluid discrimination, we propose the apparent resistivity index (ARI) as a novel method for fluid type identification. Application of the ARI successfully differentiated fluid types, demonstrating its potential as an effective method for fluid identification in fine-grained sandstones.