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<p>The presence of pyrobitumen in the reservoir not only blocked throat passages and reduced physical properties but also interfered with well logging interpretation, leading to production test failures. Taking the Longwangmiao Formation in Gaoshiti–Moxi area of the Sichuan Basin as an example, a dissolution experiment was conducted to analyze the impact of pyrobitumen on reservoir properties and logging parameters. The results showed that significant changes occurred in density, P-wave travel time, S-wave travel time, resistivity, and porosity before and after pyrobitumen dissolution. Density decreased by an average of 0.02&#xa0;g/cm<sup>3</sup>, while P-wave and S-wave travel times increased by averages of 0.524&#xa0;μs/ft and 8.919&#xa0;μs/ft, respectively. Resistivity decreased by an average of 34.47&#xa0;Ω·m. After pyrobitumen dissolution, gas porosity and NMR porosity increased by 1.29% and 1.33%, respectively, and their distributions remained consistent. The amount of pyrobitumen dissolution exhibited a strong correlation with rock density, resistivity, and porosity, whereas its correlation with P-wave and S-wave travel times was weak. A qualitative identification method for pyrobitumen was established, showing that RT and Rxo of pyrobitumen-bearing intervals were relatively high and that the difference between them was pronounced, while RT and Rxo of gas-bearing layers were relatively low. In addition, an NMR–conventional logging–based quantitative model for pyrobitumen was developed, in which pyrobitumen content was calculated as the difference between ϕ<sub><i>well logging</i></sub> and ϕ<sub><i>NMR</i></sub>. The results provided theoretical guidance for quantitatively identifying the content of pyrobitumen and improving the success rate of reservoir logging interpretation.</p>

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Logging response characteristics and quantitative identification model of pyrobitumen—Taking Longwangmiao Formation in the central Sichuan Basin, China as an example

  • 期刊论文

  • 出版模式：

    开放获取

  • 发表日期：

    2026年2月9日

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  • Yong Li,
  • Yang-yang Zhang,
  • Yu-yu Wu,
  • Qiang Lai,
  • Bing Xie,
  • Xiao-yan Fu,
  • Qiang Yang,
  • Shi-jia Chen,
  • Rui-jie Chen

摘要

The presence of pyrobitumen in the reservoir not only blocked throat passages and reduced physical properties but also interfered with well logging interpretation, leading to production test failures. Taking the Longwangmiao Formation in Gaoshiti–Moxi area of the Sichuan Basin as an example, a dissolution experiment was conducted to analyze the impact of pyrobitumen on reservoir properties and logging parameters. The results showed that significant changes occurred in density, P-wave travel time, S-wave travel time, resistivity, and porosity before and after pyrobitumen dissolution. Density decreased by an average of 0.02 g/cm3, while P-wave and S-wave travel times increased by averages of 0.524 μs/ft and 8.919 μs/ft, respectively. Resistivity decreased by an average of 34.47 Ω·m. After pyrobitumen dissolution, gas porosity and NMR porosity increased by 1.29% and 1.33%, respectively, and their distributions remained consistent. The amount of pyrobitumen dissolution exhibited a strong correlation with rock density, resistivity, and porosity, whereas its correlation with P-wave and S-wave travel times was weak. A qualitative identification method for pyrobitumen was established, showing that RT and Rxo of pyrobitumen-bearing intervals were relatively high and that the difference between them was pronounced, while RT and Rxo of gas-bearing layers were relatively low. In addition, an NMR–conventional logging–based quantitative model for pyrobitumen was developed, in which pyrobitumen content was calculated as the difference between ϕwell logging and ϕNMR. The results provided theoretical guidance for quantitatively identifying the content of pyrobitumen and improving the success rate of reservoir logging interpretation.