Pore Structure in Shale Tested by Low Pressure N<sub>2</sub> Adsorption Experiments: Mechanism, Geological Control and Application
The N<sub>2</sub> adsorption experiment is one of the most important methods for characterizing the pore structure of shale, as it covers the major pore size range present in such sediments. The goal of this work is to better understand both the mechanisms and application of low-pressure...
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MDPI AG
2022-07-01
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| Series: | Energies |
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| Online Access: | https://www.mdpi.com/1996-1073/15/13/4875 |
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| author | Feng Liang Qin Zhang Bin Lu Peng Chen Chi Su Yu Zhang Yu Liu |
| author_facet | Feng Liang Qin Zhang Bin Lu Peng Chen Chi Su Yu Zhang Yu Liu |
| author_sort | Feng Liang |
| collection | DOAJ |
| description | The N<sub>2</sub> adsorption experiment is one of the most important methods for characterizing the pore structure of shale, as it covers the major pore size range present in such sediments. The goal of this work is to better understand both the mechanisms and application of low-pressure nitrogen adsorption experiments in pore structure characterization. To achieve this, the N<sub>2</sub> adsorption molecular simulation method, low-pressure N<sub>2</sub> adsorption experiments, total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and a total of 196 shale samples from the Wufeng–Longmaxi formations in the Sichuan basin have been employed in this study. Based on the analytical data and the simulations, two parameters, the connectivity index and the large pore volume index, are proposed. These parameters are defined as the connectivity of the pore system and the volume of large nanopores (>10 nm) respectively, and they are calculated based on the N<sub>2</sub> adsorption and desorption isotherms. The experimental results showed that TOC content and clay minerals are the key factors controlling surface area and pore volume. However, in different shale wells and different substrata (divided based on graptolite zonation), the relative influences of TOC content and clay minerals on pore structure differ. In three of the six wells, TOC content is the key factor controlling surface area and pore volume. In contrast, clay minerals in samples from the W202 well are the key factors controlling pore volume, and with an increase in the clay mineral content, the pore volume increases linearly. When the carbonate content exceeds 50%, the pore volume decreases with an increase in carbonate content, and this may be because in the diagenetic process, carbonate cement fills the pores. It is also found that with increasing TOC content the connectivity index increases and SEM images also illustrate that organic pores have better connectivity. Furthermore, the connectivity index increases as quartz content increases. The large pore volume index increases with quartz content from 0 to 40% and decreases as quartz increases from 40% to 100%. By comparing the pore structure of shale in the same substrata of different shale gas wells, it was found that tectonic location significantly affects the surface area and pore volume of shale samples. The shale samples from wells that are located in broad tectonic zones, far from large-scale faults and overpressure zones, have larger pore volumes and surface areas. On the contrary, the shale samples from shale gas wells that are located in the anticline region with strong tectonic extrusion zones or near large-scale faults have relatively low pore volumes and surface areas. By employing large numbers of shale samples and analyzing N<sub>2</sub> adsorption mechanism in shale, this study has expanded the application of N<sub>2</sub> adsorption experiment in shale and clarifies the effects of sedimentary factors and tectonic factors on pore structure. |
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| issn | 1996-1073 |
| language | English |
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| spelling | doaj.art-badc6f8bf29446b1ab958f162264ba632023-11-23T19:58:48ZengMDPI AGEnergies1996-10732022-07-011513487510.3390/en15134875Pore Structure in Shale Tested by Low Pressure N<sub>2</sub> Adsorption Experiments: Mechanism, Geological Control and ApplicationFeng Liang0Qin Zhang1Bin Lu2Peng Chen3Chi Su4Yu Zhang5Yu Liu6National Energy Shale Gas R&D (Experiment) Center, Langfang 065007, ChinaNational Energy Shale Gas R&D (Experiment) Center, Langfang 065007, ChinaNational Energy Shale Gas R&D (Experiment) Center, Langfang 065007, ChinaNational Energy Shale Gas R&D (Experiment) Center, Langfang 065007, ChinaInstitute of Geology and Geophysics, Chinese Academy of Sciences, Beijing 100029, ChinaKey Laboratory for Thermal Science and Power Engineering of Ministry of Education, Tsinghua University, Beijing 100084, ChinaCollege of Geoscience and Survey Engineering, China University of Mining and Technology, Beijing 100083, ChinaThe N<sub>2</sub> adsorption experiment is one of the most important methods for characterizing the pore structure of shale, as it covers the major pore size range present in such sediments. The goal of this work is to better understand both the mechanisms and application of low-pressure nitrogen adsorption experiments in pore structure characterization. To achieve this, the N<sub>2</sub> adsorption molecular simulation method, low-pressure N<sub>2</sub> adsorption experiments, total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and a total of 196 shale samples from the Wufeng–Longmaxi formations in the Sichuan basin have been employed in this study. Based on the analytical data and the simulations, two parameters, the connectivity index and the large pore volume index, are proposed. These parameters are defined as the connectivity of the pore system and the volume of large nanopores (>10 nm) respectively, and they are calculated based on the N<sub>2</sub> adsorption and desorption isotherms. The experimental results showed that TOC content and clay minerals are the key factors controlling surface area and pore volume. However, in different shale wells and different substrata (divided based on graptolite zonation), the relative influences of TOC content and clay minerals on pore structure differ. In three of the six wells, TOC content is the key factor controlling surface area and pore volume. In contrast, clay minerals in samples from the W202 well are the key factors controlling pore volume, and with an increase in the clay mineral content, the pore volume increases linearly. When the carbonate content exceeds 50%, the pore volume decreases with an increase in carbonate content, and this may be because in the diagenetic process, carbonate cement fills the pores. It is also found that with increasing TOC content the connectivity index increases and SEM images also illustrate that organic pores have better connectivity. Furthermore, the connectivity index increases as quartz content increases. The large pore volume index increases with quartz content from 0 to 40% and decreases as quartz increases from 40% to 100%. By comparing the pore structure of shale in the same substrata of different shale gas wells, it was found that tectonic location significantly affects the surface area and pore volume of shale samples. The shale samples from wells that are located in broad tectonic zones, far from large-scale faults and overpressure zones, have larger pore volumes and surface areas. On the contrary, the shale samples from shale gas wells that are located in the anticline region with strong tectonic extrusion zones or near large-scale faults have relatively low pore volumes and surface areas. By employing large numbers of shale samples and analyzing N<sub>2</sub> adsorption mechanism in shale, this study has expanded the application of N<sub>2</sub> adsorption experiment in shale and clarifies the effects of sedimentary factors and tectonic factors on pore structure.https://www.mdpi.com/1996-1073/15/13/4875pore structureshale gasN<sub>2</sub> adsorption experimentmolecular simulationpore connectivity |
| spellingShingle | Feng Liang Qin Zhang Bin Lu Peng Chen Chi Su Yu Zhang Yu Liu Pore Structure in Shale Tested by Low Pressure N<sub>2</sub> Adsorption Experiments: Mechanism, Geological Control and Application Energies pore structure shale gas N<sub>2</sub> adsorption experiment molecular simulation pore connectivity |
| title | Pore Structure in Shale Tested by Low Pressure N<sub>2</sub> Adsorption Experiments: Mechanism, Geological Control and Application |
| title_full | Pore Structure in Shale Tested by Low Pressure N<sub>2</sub> Adsorption Experiments: Mechanism, Geological Control and Application |
| title_fullStr | Pore Structure in Shale Tested by Low Pressure N<sub>2</sub> Adsorption Experiments: Mechanism, Geological Control and Application |
| title_full_unstemmed | Pore Structure in Shale Tested by Low Pressure N<sub>2</sub> Adsorption Experiments: Mechanism, Geological Control and Application |
| title_short | Pore Structure in Shale Tested by Low Pressure N<sub>2</sub> Adsorption Experiments: Mechanism, Geological Control and Application |
| title_sort | pore structure in shale tested by low pressure n sub 2 sub adsorption experiments mechanism geological control and application |
| topic | pore structure shale gas N<sub>2</sub> adsorption experiment molecular simulation pore connectivity |
| url | https://www.mdpi.com/1996-1073/15/13/4875 |
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