Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production
Pore structure characteristics, gas content, and micro-scale gas occurrence mechanisms were investigated in the Shan23 sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images, low-temperature N2/CO2 adsorption and high-...
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KeAi Communications Co., Ltd.
2025-06-01
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| Series: | Natural Gas Industry B |
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| Online Access: | http://www.sciencedirect.com/science/article/pii/S2352854025000373 |
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| author | Guangyin Cai Yifan Gu Dongjun Song Yuqiang Jiang Yonghong Fu Ying Liu Fan Zhang Jiaxun Lu Zhen Qiu |
| author_facet | Guangyin Cai Yifan Gu Dongjun Song Yuqiang Jiang Yonghong Fu Ying Liu Fan Zhang Jiaxun Lu Zhen Qiu |
| author_sort | Guangyin Cai |
| collection | DOAJ |
| description | Pore structure characteristics, gas content, and micro-scale gas occurrence mechanisms were investigated in the Shan23 sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images, low-temperature N2/CO2 adsorption and high-pressure mercury intrusion, methane isothermal adsorption experiments, and CH4-saturated nuclear magnetic resonance (NMR). Two distinct shale types were identified: organic pore-rich shale (Type OP) and microfracture-rich shale (Type M). The Type OP shale exhibited relatively well-developed organic matter pores, while the Type M shale was primarily characterized by a high degree of microfracture development. An experimental method combining methane isothermal adsorption on crushed samples and CH4-saturated NMR of plug samples was proposed to determine the adsorbed gas, free gas, and total gas content under high temperature and pressure conditions. There were four main research findings. (1) Marine-continental transitional shale exhibited substantial total gas content in situ, ranging from 2.58 to 5.73 cm3/g, with an average of 4.35 cm3/g. The adsorbed gas primarily resided in organic matter pores through micropore filling and multilayer adsorption, followed by multilayer adsorption in clay pores. (2) The changes in adsorbed and free pore volumes can be divided into four stages. Pores of <5 nm exclusively contain adsorbed gas, while those of 5–20 nm have a high proportion of adsorbed gas alongside free gas. Pores ranging from 20 to 100 nm have a high proportion of free gas and few adsorbed gas, while pores of >100 nm and microfractures are almost predominantly free gas. (3) The proportion of adsorbed gas in Type OP shale exceeds that in Type M, reaching 66 %. (4) Methane adsorbed in Type OP shale demonstrates greater desorption capability, suggesting a potential for enhanced stable production, which finds support in existing production well data. However, it must be emphasized that high-gas-bearing intervals in both types present valuable opportunities for exploration and development. These data may support future model validations and enhance confidence in exploring and developing marine-continental transitional shale gas. |
| format | Article |
| id | doaj-art-26f0648c32ad490eacec1cea66c258aa |
| institution | OA Journals |
| issn | 2352-8540 |
| language | English |
| publishDate | 2025-06-01 |
| publisher | KeAi Communications Co., Ltd. |
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| series | Natural Gas Industry B |
| spelling | doaj-art-26f0648c32ad490eacec1cea66c258aa2025-08-20T02:37:45ZengKeAi Communications Co., Ltd.Natural Gas Industry B2352-85402025-06-0112336838510.1016/j.ngib.2025.05.009Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas productionGuangyin Cai0Yifan Gu1Dongjun Song2Yuqiang Jiang3Yonghong Fu4Ying Liu5Fan Zhang6Jiaxun Lu7Zhen Qiu8PetroChina Research Institute of Petroleum Exploration and Development, Beijing 10083, China; PetroChina Unconventional Key Laboratory, Southwest Petroleum University, Chengdu 610500, China; School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, ChinaPetroChina Unconventional Key Laboratory, Southwest Petroleum University, Chengdu 610500, China; School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, China; Corresponding author. PetroChina Unconventional Key Laboratory, Southwest Petroleum University, Chengdu 610500, China.School of Earth Sciences, Lanzhou University, Lanzhou 730000, ChinaPetroChina Unconventional Key Laboratory, Southwest Petroleum University, Chengdu 610500, China; School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, ChinaPetroChina Unconventional Key Laboratory, Southwest Petroleum University, Chengdu 610500, China; School of Geoscience and Technology, Southwest Petroleum University, Chengdu 610500, ChinaPetroChina Coalbed Methane Company, Beijing 100028, ChinaState Key Laboratory of Oil and Gas Reservoir Geology and Exploitation, Southwest Petroleum University, Chengdu 610500, ChinaSouthern Sichuan Gas District, PetroChina Southwest Oil & Gasfield Company, Luzhou 646000, ChinaPetroChina Research Institute of Petroleum Exploration and Development, Beijing 10083, China; Corresponding author.Pore structure characteristics, gas content, and micro-scale gas occurrence mechanisms were investigated in the Shan23 sub-member marine-continental transitional shale of the southeastern margin of the Ordos Basin using scanning electron microscope images, low-temperature N2/CO2 adsorption and high-pressure mercury intrusion, methane isothermal adsorption experiments, and CH4-saturated nuclear magnetic resonance (NMR). Two distinct shale types were identified: organic pore-rich shale (Type OP) and microfracture-rich shale (Type M). The Type OP shale exhibited relatively well-developed organic matter pores, while the Type M shale was primarily characterized by a high degree of microfracture development. An experimental method combining methane isothermal adsorption on crushed samples and CH4-saturated NMR of plug samples was proposed to determine the adsorbed gas, free gas, and total gas content under high temperature and pressure conditions. There were four main research findings. (1) Marine-continental transitional shale exhibited substantial total gas content in situ, ranging from 2.58 to 5.73 cm3/g, with an average of 4.35 cm3/g. The adsorbed gas primarily resided in organic matter pores through micropore filling and multilayer adsorption, followed by multilayer adsorption in clay pores. (2) The changes in adsorbed and free pore volumes can be divided into four stages. Pores of <5 nm exclusively contain adsorbed gas, while those of 5–20 nm have a high proportion of adsorbed gas alongside free gas. Pores ranging from 20 to 100 nm have a high proportion of free gas and few adsorbed gas, while pores of >100 nm and microfractures are almost predominantly free gas. (3) The proportion of adsorbed gas in Type OP shale exceeds that in Type M, reaching 66 %. (4) Methane adsorbed in Type OP shale demonstrates greater desorption capability, suggesting a potential for enhanced stable production, which finds support in existing production well data. However, it must be emphasized that high-gas-bearing intervals in both types present valuable opportunities for exploration and development. These data may support future model validations and enhance confidence in exploring and developing marine-continental transitional shale gas.http://www.sciencedirect.com/science/article/pii/S2352854025000373Marine-continental transitional shaleShale gas contentMicro-scale shale gas occurrence characteristicsProduction practice |
| spellingShingle | Guangyin Cai Yifan Gu Dongjun Song Yuqiang Jiang Yonghong Fu Ying Liu Fan Zhang Jiaxun Lu Zhen Qiu Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production Natural Gas Industry B Marine-continental transitional shale Shale gas content Micro-scale shale gas occurrence characteristics Production practice |
| title | Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production |
| title_full | Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production |
| title_fullStr | Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production |
| title_full_unstemmed | Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production |
| title_short | Gas occurrence characteristics in marine-continental transitional shale from Shan23 sub-member shale in the Ordos Basin: Implications for shale gas production |
| title_sort | gas occurrence characteristics in marine continental transitional shale from shan23 sub member shale in the ordos basin implications for shale gas production |
| topic | Marine-continental transitional shale Shale gas content Micro-scale shale gas occurrence characteristics Production practice |
| url | http://www.sciencedirect.com/science/article/pii/S2352854025000373 |
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