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<p>The accuracy of saturation evaluation in organic matter (OM)-rich shale reservoirs via electric logging remains insufficient. This study addresses the issue by integrating litho-electric experiments and nuclear magnetic resonance (NMR) analysis, focusing on organic-rich shale samples from the Wangqing area, peripheral to the Songliao Basin. Laboratory tests analyzed mineral composition, OM characteristics, and fluid occurrence states, while litho-electric experiments and NMR measurements investigated the resistivity (<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\({R}_{t}\)</EquationSource> </InlineEquation>) and water saturation (<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\({S}_{w}\)</EquationSource> </InlineEquation>) relationship. Key findings reveal that the distribution at varying saturations dominates&#xa0;<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\({R}_{t}\)</EquationSource> </InlineEquation>, with high OM content significantly elevates&#xa0;<InlineEquation ID="IEq4"> <EquationSource Format="TEX">\({R}_{t}\)</EquationSource> </InlineEquation>&#xa0;due to its non-conductive nature and obstruction of conductive pathways. These results highlight the need to incorporate fluid distribution heterogeneity and anisotropic into saturation models. The proposed variable n-value Archie equation, which dynamically adjusting the saturation exponent n based on&#xa0;<InlineEquation ID="IEq5"> <EquationSource Format="TEX">\({S}_{w}\)</EquationSource> </InlineEquation>​, and achieves a fitting goodness (R<sup>2</sup> = 0.98), significantly outperforming the traditional Archie model (R<sup>2</sup> = 0.44–0.48), providing a refined approach for evaluatingcomplex shale systems.</p>

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A variable n-value Archie model for saturation evaluation in organic-rich shales by litho-electric experiments

  • 期刊论文

  • 出版模式：

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  • 发表日期：

    2025年11月6日

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  • Jian Lei,
  • Yufei Fan

摘要

The accuracy of saturation evaluation in organic matter (OM)-rich shale reservoirs via electric logging remains insufficient. This study addresses the issue by integrating litho-electric experiments and nuclear magnetic resonance (NMR) analysis, focusing on organic-rich shale samples from the Wangqing area, peripheral to the Songliao Basin. Laboratory tests analyzed mineral composition, OM characteristics, and fluid occurrence states, while litho-electric experiments and NMR measurements investigated the resistivity ( \({R}_{t}\) ) and water saturation ( \({S}_{w}\) ) relationship. Key findings reveal that the distribution at varying saturations dominates  \({R}_{t}\) , with high OM content significantly elevates  \({R}_{t}\)  due to its non-conductive nature and obstruction of conductive pathways. These results highlight the need to incorporate fluid distribution heterogeneity and anisotropic into saturation models. The proposed variable n-value Archie equation, which dynamically adjusting the saturation exponent n based on  \({S}_{w}\) ​, and achieves a fitting goodness (R2 = 0.98), significantly outperforming the traditional Archie model (R2 = 0.44–0.48), providing a refined approach for evaluatingcomplex shale systems.