Authigenic silica in continental lacustrine shale and its hydrocarbon significance
Taking lake basin shales of the Triassic Yanchang Formation in the Ordos Basin, NW China and the Cretaceous Qingshankou Formation in the Songliao Basin, NE China as research objects, the characteristics and origins of different types of silica in the shales have been studied by means of core observa...
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| Format: | Article |
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KeAi Communications Co., Ltd.
2022-10-01
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| Series: | Petroleum Exploration and Development |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S1876380422603306 |
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| author | Bin BAI Chaocheng DAI Xiulin HOU Xianyang LIU Rui WANG Liang YANG Shixiang LI Junling HE Ruojing DONG |
| author_facet | Bin BAI Chaocheng DAI Xiulin HOU Xianyang LIU Rui WANG Liang YANG Shixiang LI Junling HE Ruojing DONG |
| author_sort | Bin BAI |
| collection | DOAJ |
| description | Taking lake basin shales of the Triassic Yanchang Formation in the Ordos Basin, NW China and the Cretaceous Qingshankou Formation in the Songliao Basin, NE China as research objects, the characteristics and origins of different types of silica in the shales have been studied by means of core observation, thin section identification, cathodoluminescence, X-ray diffraction analysis, scanning electron microscope (SEM), electron probe and rock pyrolysis. The results shows that the origins of silica include felsic mineral dissolution, tuffite devitrification, clay mineral transformation and siliceous mineral metasomatism. The silica formed by feldspar dissolution commonly appears as spots and veins, with low degree of crystallization, and is largely aqueous opal mineral, with an average SiO2 content of 67.2%. Silica formed by devitrification of tuffite mainly occurs in two forms, amorphous silica and authigenic quartz with better crystal shape. The authigenic silica formed during the transformation of clay minerals is embedded in the clay minerals in the form of micron-scale plates and small flakes, or mixed with clay minerals in a dispersed state. The authigenic quartz formed by siliceous mineral metasomatism is in better angular crystal shape, and has an average SiO2 content of 87%. The authigenic siliceous mineral content is positively correlated with the content of terrigenous felsic minerals. The pressure solution of felsic minerals is the main source of authigenic siliceous minerals, followed by the transformation of clay minerals, and the organic matter has some boost on the formation of authigenic silica. The authigenic siliceous materials of different origins have different geological characteristics and occurrence states from terrigenous quartz, which would affect the storage performance, seepage capacity and fracturing effect of continental shale. Although the organic-rich shale has high silica content, different from terrigenous quartz, authigenic silica in this kind of shale mostly floats and disperse in clay minerals, which would have negative effect on the formation of complex fractures in fracturing, fracture support ability after fracturing, and formation of effective seepage channels. Calculating the brittleness index of shale intervals only based on the composition of brittle minerals cannot accurately characterize mechanical characteristics of continental shale oil reservoirs, and would affect comprehensive evaluation and selection of continental shale oil “sweet spots”. |
| first_indexed | 2024-04-13T18:34:10Z |
| format | Article |
| id | doaj.art-63a169293d81476b9f9669ba00617d3c |
| institution | Directory Open Access Journal |
| issn | 1876-3804 |
| language | English |
| last_indexed | 2024-04-13T18:34:10Z |
| publishDate | 2022-10-01 |
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| series | Petroleum Exploration and Development |
| spelling | doaj.art-63a169293d81476b9f9669ba00617d3c2022-12-22T02:34:56ZengKeAi Communications Co., Ltd.Petroleum Exploration and Development1876-38042022-10-0149510331045Authigenic silica in continental lacustrine shale and its hydrocarbon significanceBin BAI0Chaocheng DAI1Xiulin HOU2Xianyang LIU3Rui WANG4Liang YANG5Shixiang LI6Junling HE7Ruojing DONG8PetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, China; Corresponding authorSchool of Earth Sciences, East China University of Technology, Nanchang 330000, ChinaPetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, ChinaExploration and Development Research Institute of PetroChina Changqing Oilfield Company, Xi'an 710018, ChinaPetroChina Daqing Oilfield Company, Daqing 163453, ChinaExploration and Development Research Institute of PetroChina Jilin Oilfield Company, Songyuan 138099, ChinaExploration and Development Research Institute of PetroChina Changqing Oilfield Company, Xi'an 710018, ChinaExploration and Development Research Institute of PetroChina Jilin Oilfield Company, Songyuan 138099, ChinaPetroChina Research Institute of Petroleum Exploration & Development, Beijing 100083, ChinaTaking lake basin shales of the Triassic Yanchang Formation in the Ordos Basin, NW China and the Cretaceous Qingshankou Formation in the Songliao Basin, NE China as research objects, the characteristics and origins of different types of silica in the shales have been studied by means of core observation, thin section identification, cathodoluminescence, X-ray diffraction analysis, scanning electron microscope (SEM), electron probe and rock pyrolysis. The results shows that the origins of silica include felsic mineral dissolution, tuffite devitrification, clay mineral transformation and siliceous mineral metasomatism. The silica formed by feldspar dissolution commonly appears as spots and veins, with low degree of crystallization, and is largely aqueous opal mineral, with an average SiO2 content of 67.2%. Silica formed by devitrification of tuffite mainly occurs in two forms, amorphous silica and authigenic quartz with better crystal shape. The authigenic silica formed during the transformation of clay minerals is embedded in the clay minerals in the form of micron-scale plates and small flakes, or mixed with clay minerals in a dispersed state. The authigenic quartz formed by siliceous mineral metasomatism is in better angular crystal shape, and has an average SiO2 content of 87%. The authigenic siliceous mineral content is positively correlated with the content of terrigenous felsic minerals. The pressure solution of felsic minerals is the main source of authigenic siliceous minerals, followed by the transformation of clay minerals, and the organic matter has some boost on the formation of authigenic silica. The authigenic siliceous materials of different origins have different geological characteristics and occurrence states from terrigenous quartz, which would affect the storage performance, seepage capacity and fracturing effect of continental shale. Although the organic-rich shale has high silica content, different from terrigenous quartz, authigenic silica in this kind of shale mostly floats and disperse in clay minerals, which would have negative effect on the formation of complex fractures in fracturing, fracture support ability after fracturing, and formation of effective seepage channels. Calculating the brittleness index of shale intervals only based on the composition of brittle minerals cannot accurately characterize mechanical characteristics of continental shale oil reservoirs, and would affect comprehensive evaluation and selection of continental shale oil “sweet spots”.http://www.sciencedirect.com/science/article/pii/S1876380422603306continental lake basinorganic-rich shaleauthigenic quartzQingshankou FormationYanchang FormationOrdos Basin |
| spellingShingle | Bin BAI Chaocheng DAI Xiulin HOU Xianyang LIU Rui WANG Liang YANG Shixiang LI Junling HE Ruojing DONG Authigenic silica in continental lacustrine shale and its hydrocarbon significance Petroleum Exploration and Development continental lake basin organic-rich shale authigenic quartz Qingshankou Formation Yanchang Formation Ordos Basin |
| title | Authigenic silica in continental lacustrine shale and its hydrocarbon significance |
| title_full | Authigenic silica in continental lacustrine shale and its hydrocarbon significance |
| title_fullStr | Authigenic silica in continental lacustrine shale and its hydrocarbon significance |
| title_full_unstemmed | Authigenic silica in continental lacustrine shale and its hydrocarbon significance |
| title_short | Authigenic silica in continental lacustrine shale and its hydrocarbon significance |
| title_sort | authigenic silica in continental lacustrine shale and its hydrocarbon significance |
| topic | continental lake basin organic-rich shale authigenic quartz Qingshankou Formation Yanchang Formation Ordos Basin |
| url | http://www.sciencedirect.com/science/article/pii/S1876380422603306 |
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