Analysis of the controlling factors for sweet spots in lacustrine shale based on core experiments and 2D NMR logging
Abstract The Gulong shale in the Songliao Basin, characterized by its high clay content, poses significant challenges for the identification of sweet spots. To address this, a novel temperature-dependent retorting and 2D NMR joint experimental approach was developed to investigate the fluid characte...
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Nature Portfolio
2025-07-01
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| Online Access: | https://doi.org/10.1038/s41598-025-04771-1 |
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| author | Zhaoqian Zhang Yanjie Song Shujun Yin Bo Liu Haibo Zhao Weilin Yan Jiandong Zheng |
| author_facet | Zhaoqian Zhang Yanjie Song Shujun Yin Bo Liu Haibo Zhao Weilin Yan Jiandong Zheng |
| author_sort | Zhaoqian Zhang |
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| description | Abstract The Gulong shale in the Songliao Basin, characterized by its high clay content, poses significant challenges for the identification of sweet spots. To address this, a novel temperature-dependent retorting and 2D NMR joint experimental approach was developed to investigate the fluid characteristics of the Gulong shale under varying occurrence states. The experimental results demonstrated that the pore fluids in Gulong shale are composed of multiple components, including free water, capillary bound water, clay bound water, bound oil in small inorganic pores, adsorbed oil in organic pores, free oil in large inorganic pores, and bitumen. In addition to these fluid components, the solid components consist of clay mineral assemblages (hydroxyl groups) and kerogen, collectively making up a total of eight distinct components. Furthermore, a comprehensive T1–T2 interpretation framework was established based on the retorting and NMR joint experiments, providing a robust tool for guiding fluid type classification using 2D NMR logging data. Analysis of advanced NMR T1–T2 logs indicated the absence of free water in the Gulong shale. A strong correlation was observed between the normalized annual production of the horizontal section per kilometer and the free oil porosity, with the ten horizontal wells targeting high free oil content layers demonstrating the highest productivity. Additional investigations using elemental spectroscopy logging and field emission-scanning electron microscopy (FE-SEM) revealed that layers with high free oil content are associated with larger particle sizes, leading to the development of enlarged inorganic macropores. These findings provide critical insights into the key geological controls governing sweet spots in the Gulong shale, offering valuable guidance for reservoir evaluation and development. |
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| institution | DOAJ |
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| language | English |
| publishDate | 2025-07-01 |
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| spelling | doaj-art-8a7a89b31f4c4ada9dcd96dce5f83e142025-08-20T03:03:32ZengNature PortfolioScientific Reports2045-23222025-07-0115112410.1038/s41598-025-04771-1Analysis of the controlling factors for sweet spots in lacustrine shale based on core experiments and 2D NMR loggingZhaoqian Zhang0Yanjie Song1Shujun Yin2Bo Liu3Haibo Zhao4Weilin Yan5Jiandong Zheng6School of Earth Sciences, Northeast Petroleum UniversitySchool of Earth Sciences, Northeast Petroleum UniversityExploration and Development Research Institute, PetroChina Daqing Oilfield Co. Ltd.Institute of Unconventional Oil and Gas, Northeast Petroleum UniversityExploration and Development Research Institute, PetroChina Daqing Oilfield Co. Ltd.Exploration and Development Research Institute, PetroChina Daqing Oilfield Co. Ltd.Exploration and Development Research Institute, PetroChina Daqing Oilfield Co. Ltd.Abstract The Gulong shale in the Songliao Basin, characterized by its high clay content, poses significant challenges for the identification of sweet spots. To address this, a novel temperature-dependent retorting and 2D NMR joint experimental approach was developed to investigate the fluid characteristics of the Gulong shale under varying occurrence states. The experimental results demonstrated that the pore fluids in Gulong shale are composed of multiple components, including free water, capillary bound water, clay bound water, bound oil in small inorganic pores, adsorbed oil in organic pores, free oil in large inorganic pores, and bitumen. In addition to these fluid components, the solid components consist of clay mineral assemblages (hydroxyl groups) and kerogen, collectively making up a total of eight distinct components. Furthermore, a comprehensive T1–T2 interpretation framework was established based on the retorting and NMR joint experiments, providing a robust tool for guiding fluid type classification using 2D NMR logging data. Analysis of advanced NMR T1–T2 logs indicated the absence of free water in the Gulong shale. A strong correlation was observed between the normalized annual production of the horizontal section per kilometer and the free oil porosity, with the ten horizontal wells targeting high free oil content layers demonstrating the highest productivity. Additional investigations using elemental spectroscopy logging and field emission-scanning electron microscopy (FE-SEM) revealed that layers with high free oil content are associated with larger particle sizes, leading to the development of enlarged inorganic macropores. These findings provide critical insights into the key geological controls governing sweet spots in the Gulong shale, offering valuable guidance for reservoir evaluation and development.https://doi.org/10.1038/s41598-025-04771-1Shale oilHigh clay contentSweet spots2D NMR logsSongliao basinGulong Sag |
| spellingShingle | Zhaoqian Zhang Yanjie Song Shujun Yin Bo Liu Haibo Zhao Weilin Yan Jiandong Zheng Analysis of the controlling factors for sweet spots in lacustrine shale based on core experiments and 2D NMR logging Scientific Reports Shale oil High clay content Sweet spots 2D NMR logs Songliao basin Gulong Sag |
| title | Analysis of the controlling factors for sweet spots in lacustrine shale based on core experiments and 2D NMR logging |
| title_full | Analysis of the controlling factors for sweet spots in lacustrine shale based on core experiments and 2D NMR logging |
| title_fullStr | Analysis of the controlling factors for sweet spots in lacustrine shale based on core experiments and 2D NMR logging |
| title_full_unstemmed | Analysis of the controlling factors for sweet spots in lacustrine shale based on core experiments and 2D NMR logging |
| title_short | Analysis of the controlling factors for sweet spots in lacustrine shale based on core experiments and 2D NMR logging |
| title_sort | analysis of the controlling factors for sweet spots in lacustrine shale based on core experiments and 2d nmr logging |
| topic | Shale oil High clay content Sweet spots 2D NMR logs Songliao basin Gulong Sag |
| url | https://doi.org/10.1038/s41598-025-04771-1 |
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