The Volcanic Impacts on the Formation of Organic-Rich Shales From the Freshwater to Saline Lakes: Cases Study in the Ordos and the Junggar Basins
High organic matter abundance is necessary for large-scale hydrocarbon accumulation and enrichment in shale oil. Comparing conventional marine basins with lacustrine ones, the formation of organic matter in the latter usually changes rapidly with strong heterogeneity, which brings great challenges t...
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| Format: | Article |
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Frontiers Media S.A.
2022-05-01
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| Series: | Frontiers in Earth Science |
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| Online Access: | https://www.frontiersin.org/articles/10.3389/feart.2022.918391/full |
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| author | Xiaojun Wang Jiahong Gao Liang Zhong Wenjun He Zhijun Jin Rukai Zhu Rukai Zhu Xinping Liang Kouqi Liu Wang Zhang |
| author_facet | Xiaojun Wang Jiahong Gao Liang Zhong Wenjun He Zhijun Jin Rukai Zhu Rukai Zhu Xinping Liang Kouqi Liu Wang Zhang |
| author_sort | Xiaojun Wang |
| collection | DOAJ |
| description | High organic matter abundance is necessary for large-scale hydrocarbon accumulation and enrichment in shale oil. Comparing conventional marine basins with lacustrine ones, the formation of organic matter in the latter usually changes rapidly with strong heterogeneity, which brings great challenges to identify sweet spot prediction and resource evaluation. In addition, water columns with different redox conditions also affect the burial and preservation of organic matter during the deposition of lacustrine shales, especially under the impact of ephemeral critical geological events such as volcanic activities. Therefore, determining the properties and the influencing factors on the water columns is one of the key scientific issues in revealing the differential enrichment of organic matter in such basins. By comparing the petrological and geochemical characteristics of organic-rich shales between a typical freshwater and a saline lacustrine basin, this study analyzes the depositional environment and water column properties during the burial and preservation of organic matter in the Ordos and Junggar basins. The results demonstrate that volcanic activity intensifies the degree of hypoxia during the formation of organic-rich matter, which in turn affects organic matter preservation. The sulfate reduction index (SRI) indicates that the organic-rich shale of the Chang seven Member (Ch7) of Yanchang Formation in the Ordos Basin and the Lucaogou Formation (P2l) in the Jimsar Sag of Junggar Basin in freshwater-saline environments have a certain intensity of sulfate reduction (BSR) (SRI <1.375). The organic matter consumed by BSR is lower than the preserved organic matter, resulting a higher TOC content. However, excessive volcanic activity or the input of hydrothermal fluids caused strong BSR (SRI >1.375) of the Fengcheng Formation (P2f) in saline lake of the Mahu Sag in Junggar Basin. This indicates that a large amount of organic matter was degraded and consumed, causing more iron oxides (and other iron-containing minerals) dissolve gradually to form pyrite, reducing the TOC content. This study enabled us to understand the shale oil enrichment, sweet spot prediction and evaluation, and propose a better theoretical and practical model for hydrocarbon accumulation in shale formations, to guide future exploration efforts. |
| first_indexed | 2024-04-14T05:06:32Z |
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| institution | Directory Open Access Journal |
| issn | 2296-6463 |
| language | English |
| last_indexed | 2024-04-14T05:06:32Z |
| publishDate | 2022-05-01 |
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| spelling | doaj.art-71eaa45326bf4b948112367d97be29cf2022-12-22T02:10:41ZengFrontiers Media S.A.Frontiers in Earth Science2296-64632022-05-011010.3389/feart.2022.918391918391The Volcanic Impacts on the Formation of Organic-Rich Shales From the Freshwater to Saline Lakes: Cases Study in the Ordos and the Junggar BasinsXiaojun Wang0Jiahong Gao1Liang Zhong2Wenjun He3Zhijun Jin4Rukai Zhu5Rukai Zhu6Xinping Liang7Kouqi Liu8Wang Zhang9Research Institute of Exploration and Development, PetroChina Xinjiang Oilfield Company, Karamay, ChinaInstitute of Energy, Peking University, Beijing, ChinaOperation Area of Fengcheng Oilfield, PetroChina Xinjiang Oilfield Company, Karamay, ChinaResearch Institute of Exploration and Development, PetroChina Xinjiang Oilfield Company, Karamay, ChinaInstitute of Energy, Peking University, Beijing, ChinaInstitute of Energy, Peking University, Beijing, ChinaResearch Institute of Petroleum Exploration and Development, PetroChina, Beijing, ChinaInstitute of Energy, Peking University, Beijing, ChinaInstitute of Energy, Peking University, Beijing, ChinaInstitute of Geology and Geophysics, Beijing, ChinaHigh organic matter abundance is necessary for large-scale hydrocarbon accumulation and enrichment in shale oil. Comparing conventional marine basins with lacustrine ones, the formation of organic matter in the latter usually changes rapidly with strong heterogeneity, which brings great challenges to identify sweet spot prediction and resource evaluation. In addition, water columns with different redox conditions also affect the burial and preservation of organic matter during the deposition of lacustrine shales, especially under the impact of ephemeral critical geological events such as volcanic activities. Therefore, determining the properties and the influencing factors on the water columns is one of the key scientific issues in revealing the differential enrichment of organic matter in such basins. By comparing the petrological and geochemical characteristics of organic-rich shales between a typical freshwater and a saline lacustrine basin, this study analyzes the depositional environment and water column properties during the burial and preservation of organic matter in the Ordos and Junggar basins. The results demonstrate that volcanic activity intensifies the degree of hypoxia during the formation of organic-rich matter, which in turn affects organic matter preservation. The sulfate reduction index (SRI) indicates that the organic-rich shale of the Chang seven Member (Ch7) of Yanchang Formation in the Ordos Basin and the Lucaogou Formation (P2l) in the Jimsar Sag of Junggar Basin in freshwater-saline environments have a certain intensity of sulfate reduction (BSR) (SRI <1.375). The organic matter consumed by BSR is lower than the preserved organic matter, resulting a higher TOC content. However, excessive volcanic activity or the input of hydrothermal fluids caused strong BSR (SRI >1.375) of the Fengcheng Formation (P2f) in saline lake of the Mahu Sag in Junggar Basin. This indicates that a large amount of organic matter was degraded and consumed, causing more iron oxides (and other iron-containing minerals) dissolve gradually to form pyrite, reducing the TOC content. This study enabled us to understand the shale oil enrichment, sweet spot prediction and evaluation, and propose a better theoretical and practical model for hydrocarbon accumulation in shale formations, to guide future exploration efforts.https://www.frontiersin.org/articles/10.3389/feart.2022.918391/fullvolcanic activitythe freshwater and saline lakesFengcheng FormationLucaogou FormationChang 7 Memberorganic-rich shale |
| spellingShingle | Xiaojun Wang Jiahong Gao Liang Zhong Wenjun He Zhijun Jin Rukai Zhu Rukai Zhu Xinping Liang Kouqi Liu Wang Zhang The Volcanic Impacts on the Formation of Organic-Rich Shales From the Freshwater to Saline Lakes: Cases Study in the Ordos and the Junggar Basins Frontiers in Earth Science volcanic activity the freshwater and saline lakes Fengcheng Formation Lucaogou Formation Chang 7 Member organic-rich shale |
| title | The Volcanic Impacts on the Formation of Organic-Rich Shales From the Freshwater to Saline Lakes: Cases Study in the Ordos and the Junggar Basins |
| title_full | The Volcanic Impacts on the Formation of Organic-Rich Shales From the Freshwater to Saline Lakes: Cases Study in the Ordos and the Junggar Basins |
| title_fullStr | The Volcanic Impacts on the Formation of Organic-Rich Shales From the Freshwater to Saline Lakes: Cases Study in the Ordos and the Junggar Basins |
| title_full_unstemmed | The Volcanic Impacts on the Formation of Organic-Rich Shales From the Freshwater to Saline Lakes: Cases Study in the Ordos and the Junggar Basins |
| title_short | The Volcanic Impacts on the Formation of Organic-Rich Shales From the Freshwater to Saline Lakes: Cases Study in the Ordos and the Junggar Basins |
| title_sort | volcanic impacts on the formation of organic rich shales from the freshwater to saline lakes cases study in the ordos and the junggar basins |
| topic | volcanic activity the freshwater and saline lakes Fengcheng Formation Lucaogou Formation Chang 7 Member organic-rich shale |
| url | https://www.frontiersin.org/articles/10.3389/feart.2022.918391/full |
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