Response of organic matter pore development to functional groups in overmature marine shale: Insights from AFM-IR spectroscopy
Taking the Lower Silurian Longmaxi Formation shale in the Sichuan Basin as an example, this study employs atomic force microscopy-based infrared (AFM-IR) spectroscopy to analyze the submicron-scale molecular functional groups of different types and occurrences of organic matter. Combined with the qu...
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| Format: | Article |
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KeAi Communications Co., Ltd.
2025-04-01
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| Series: | Petroleum Exploration and Development |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S1876380425605787 |
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| author | Jianhua ZHAO Keyu LIU Shenghui ZHAO Qinhong HU Wei WU Yang CHEN Guoheng LIU Junqian LI Lingjie YU Zuhui YOU Ye WANG |
| author_facet | Jianhua ZHAO Keyu LIU Shenghui ZHAO Qinhong HU Wei WU Yang CHEN Guoheng LIU Junqian LI Lingjie YU Zuhui YOU Ye WANG |
| author_sort | Jianhua ZHAO |
| collection | DOAJ |
| description | Taking the Lower Silurian Longmaxi Formation shale in the Sichuan Basin as an example, this study employs atomic force microscopy-based infrared (AFM-IR) spectroscopy to analyze the submicron-scale molecular functional groups of different types and occurrences of organic matter. Combined with the quantitative evaluation of pore development via scanning electron microscopy (SEM), the response of organic pore formation and evolution mechanisms to chemical composition and structural evolution of organic matter in overmature marine shale is investigated. The results indicate that the AFM-IR spectra of graptolite periderms and pyrobitumen in shale are dominated by the stretching vibrations of conjugated C=C bonds in aromatic compounds at approximately 1 600 cm-1, with weak absorption peaks near 1 375, 1 450 and 1 720 cm-1, corresponding to aliphatic chains and carbonyl/carboxyl functional groups. Overall, the AFM-IR structural indices (A and C factors) of organic matter show a strong correlation with visible porosity in shales of equivalent maturity. Lower A and C factor values correlate with enhanced development of organic pores, which is associated with the detachment of more aliphatic chains and oxygen-containing functional groups during thermal evolution. Pyrobitumen-clay mineral composites generally exhibit superior pore development, likely attributable to clay mineral dehydration participating in hydrocarbon generation reactions that promote the removal of more functional groups. Additionally, hydrocarbon generation within organic-clay composites during high–over mature stages may induce volumetric expansion, resulting in microfracturing and hydrocarbon expulsion. The associated higher hydrocarbon expulsion rates promote the formation of larger pores and fracture-shaped pores along the flake-shaped clay minerals. This study highlights that the research of submicron-scale molecular functional groups provides a deeper understanding of organic matter evolution and pores development mechanisms in overmature shales, thereby offering critical theoretical parameters for reservoir evaluation in shale oil and gas exploration. |
| format | Article |
| id | doaj-art-e78114c863044e2c9f027b90fe4f1614 |
| institution | OA Journals |
| issn | 1876-3804 |
| language | English |
| publishDate | 2025-04-01 |
| publisher | KeAi Communications Co., Ltd. |
| record_format | Article |
| series | Petroleum Exploration and Development |
| spelling | doaj-art-e78114c863044e2c9f027b90fe4f16142025-08-20T02:18:51ZengKeAi Communications Co., Ltd.Petroleum Exploration and Development1876-38042025-04-0152244545810.1016/S1876-3804(25)60578-7Response of organic matter pore development to functional groups in overmature marine shale: Insights from AFM-IR spectroscopyJianhua ZHAO0Keyu LIU1Shenghui ZHAO2Qinhong HU3Wei WU4Yang CHEN5Guoheng LIU6Junqian LI7Lingjie YU8Zuhui YOU9Ye WANG10State Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, ChinaState Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, China; Corresponding authorSinopec Southwest Oil & Gas Company, Chengdu 610041, ChinaState Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, ChinaShale Gas Research Institute, PetroChina Southwest Oil & Gas Field Company, Chengdu 610051, ChinaState Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, ChinaState Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, ChinaState Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, ChinaSinopec Key Laboratory of Petroleum Accumulation Mechanisms, Wuxi 214126, China; Wuxi Institute of Petroleum Geology, Sinopec Petroleum Exploration and Production Research Institute, Wuxi 214126, ChinaState Key Laboratory of Deep Oil and Gas, China University of Petroleum (East China), Qingdao 266580, ChinaKey Laboratory of Western Mineral Resources and Geological Engineering of Ministry of Education, Chang'an University, Xi'an 710054, ChinaTaking the Lower Silurian Longmaxi Formation shale in the Sichuan Basin as an example, this study employs atomic force microscopy-based infrared (AFM-IR) spectroscopy to analyze the submicron-scale molecular functional groups of different types and occurrences of organic matter. Combined with the quantitative evaluation of pore development via scanning electron microscopy (SEM), the response of organic pore formation and evolution mechanisms to chemical composition and structural evolution of organic matter in overmature marine shale is investigated. The results indicate that the AFM-IR spectra of graptolite periderms and pyrobitumen in shale are dominated by the stretching vibrations of conjugated C=C bonds in aromatic compounds at approximately 1 600 cm-1, with weak absorption peaks near 1 375, 1 450 and 1 720 cm-1, corresponding to aliphatic chains and carbonyl/carboxyl functional groups. Overall, the AFM-IR structural indices (A and C factors) of organic matter show a strong correlation with visible porosity in shales of equivalent maturity. Lower A and C factor values correlate with enhanced development of organic pores, which is associated with the detachment of more aliphatic chains and oxygen-containing functional groups during thermal evolution. Pyrobitumen-clay mineral composites generally exhibit superior pore development, likely attributable to clay mineral dehydration participating in hydrocarbon generation reactions that promote the removal of more functional groups. Additionally, hydrocarbon generation within organic-clay composites during high–over mature stages may induce volumetric expansion, resulting in microfracturing and hydrocarbon expulsion. The associated higher hydrocarbon expulsion rates promote the formation of larger pores and fracture-shaped pores along the flake-shaped clay minerals. This study highlights that the research of submicron-scale molecular functional groups provides a deeper understanding of organic matter evolution and pores development mechanisms in overmature shales, thereby offering critical theoretical parameters for reservoir evaluation in shale oil and gas exploration.http://www.sciencedirect.com/science/article/pii/S1876380425605787AFM-IR spectrumorganic matter molecular functional groupsorganic matter pore developmentLongmaxi Formation shale |
| spellingShingle | Jianhua ZHAO Keyu LIU Shenghui ZHAO Qinhong HU Wei WU Yang CHEN Guoheng LIU Junqian LI Lingjie YU Zuhui YOU Ye WANG Response of organic matter pore development to functional groups in overmature marine shale: Insights from AFM-IR spectroscopy Petroleum Exploration and Development AFM-IR spectrum organic matter molecular functional groups organic matter pore development Longmaxi Formation shale |
| title | Response of organic matter pore development to functional groups in overmature marine shale: Insights from AFM-IR spectroscopy |
| title_full | Response of organic matter pore development to functional groups in overmature marine shale: Insights from AFM-IR spectroscopy |
| title_fullStr | Response of organic matter pore development to functional groups in overmature marine shale: Insights from AFM-IR spectroscopy |
| title_full_unstemmed | Response of organic matter pore development to functional groups in overmature marine shale: Insights from AFM-IR spectroscopy |
| title_short | Response of organic matter pore development to functional groups in overmature marine shale: Insights from AFM-IR spectroscopy |
| title_sort | response of organic matter pore development to functional groups in overmature marine shale insights from afm ir spectroscopy |
| topic | AFM-IR spectrum organic matter molecular functional groups organic matter pore development Longmaxi Formation shale |
| url | http://www.sciencedirect.com/science/article/pii/S1876380425605787 |
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