Organic nanopore structure and fractal characteristics of Wufeng and lower member of Longmaxi shales in southeastern Sichuan, China

Peng, Nyujia; He, Sheng; Hu, Qinhong; Zhang, Boqiao; Xu, He; Zhai, Gangyi; He, Chencheng; Yang, Rui

doi:10.1016/j.marpetgeo.2019.03.017

Cited by 61 publications

(57 citation statements)

References 49 publications

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“…Organic pores derived through the hydrocarbon generation process are crucial for marine shale. Previous studies have largely revealed the nanoscale pore system of mature marine shales all over the world and realized that the organic pores developed as a result of devolatilization of gaseous hydrocarbons are the dominated pore type and are responsible for the storage of shale gas to a great extent (Loucks et al, 2009;Milliken et al, 2013;Yang et al, 2013;Loucks and Reed, 2014;Wang et al, 2015;Yu et al, 2016;Guo et al, 2017;Ji et al, 2017;Nie et al, 2019;Peng et al, 2019;Xi et al, 2019). In China, the marine shale from the Lower Silurian Longmaxi Formation has been proved to be the most favorable exploitation target, and several shale-gas fields have been put into production .…”

Section: Introductionmentioning

confidence: 99%

Composition Effect on the Pore Structure of Transitional Shale: A Case Study of the Permian Shanxi Formation in the Daning–Jixian Block at the Eastern Margin of the Ordos Basin

et al. 2022

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Marine–continental transitional (hereinafter referred to as transitional) Permian shales are important targets for shale gas in China because of the considerable volumes of shale gas resources present in them. In this study, transitional shale samples from the Permian Shanxi Formation in the Daning–Jixian block along the eastern margin of the Ordos Basin were collected to investigate the effects of organic and inorganic compositions on the development of their pore structures through organic petrographic analysis, X–ray diffraction, scanning electron microscope (SEM) observation, gas (N2 and CO2) adsorption, high-pressure mercury injection (HPMI), and methane adsorption experiments. The organic petrographic analysis reveals that the Permian Shanxi shale comprises Type-II2-III kerogens, and the average vitrinite reflectance (Ro) is 2.3% at the overmature stage or in the dry gas window. The shale interval at the bottom of the lagoon facies is considered the most favorable interval throughout the entire section because of its high total organic carbon (TOC) content (4.19–43.9%; an average of 16.9%) and high brittle mineral content (38.3–73.2%; an average of 55.8%). N2 and CO2 gas adsorption and HPMI tests reveal the pore size distribution characteristics of the shale. The full pore size distribution by the gas adsorption and HPMI test reveals that micropores (<2 nm) and mesopores (2–50 nm) were dominant in the pore system, and the contributions of the two pore sizes were nearly equivalent, accounting for 21.95–55.05% (an average of 42.3%) and 37.94–64.6% (an average of 49.64%) of the total pore volume, respectively. Additionally, the pore characteristics related to different phases (mainly as silicate, clays, and organic matter) are further clarified by SEM observation and correlation analysis of phase content and pore structure parameters. OM contains numerous SEM-invisible micropores, whereas clay minerals mainly develop mesopores and small macropores (50–100 nm). Furthermore, we calculated the contribution of different shale components to shale porosity. The OM pores account for 0.26–44.1% (an average of 18.7%), and clay mineral pores account for 53.8–93.3% (an average of 76.9%) of the shale porosity. In particular, the OM contributes 73.2% to the surface area and 33.5% to the pore volume. This implies that both OM and clay minerals are important for the storage capacity of adsorbed and free gas.

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Section: Introductionmentioning

confidence: 99%

Composition Effect on the Pore Structure of Transitional Shale: A Case Study of the Permian Shanxi Formation in the Daning–Jixian Block at the Eastern Margin of the Ordos Basin

et al. 2022

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“…Figure 2 shows the N 2 adsorption-desorption isotherm of the selected deformed shale samples. Combining with previous studies, obviously, to summarize the pore morphology characteristics in shale can be inferred based on the type of N 2 adsorption-desorption isotherm and the shape of the hysteresis loop [8,11,44]. In accordance with the IUPAC classification of the hysteresis loops, the N 2 adsorptiondesorption isotherm of the shale samples belongs to Types H2 and H3 [11,[45][46][47][48].…”

Section: Geofluidsmentioning

confidence: 55%

Relationship between Tectonism and Composition and Pore Characteristics of Shale Reservoirs

et al. 2020

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Tectonism is one of the major controlling factors of shale gas accumulation and enrichment in China. To explore the relationship between tectonism and composition and pore characteristics of shale reservoirs, this research carried out mineralogy tests, organic geochemistry tests, field emission scanning electron microscopy (FE-SEM) experiments, and low-pressure gas adsorption (LPGA, N2 and CO2) experiments on the shale samples of various deformation intensities from Southwestern China. Based on the FE-SEM image analyses, it can be found that there are large differences in pore characteristics in shale samples with different deformation intensities. The samples with strong deformation have more organic pores, mainly related to the clay-organic aggregates and rigid grains. Tectonism can cause organic matter (OM) and clay minerals to be mixed or OM to fill in the clay layers, resulting in the retention of some organic pores. It is the presence of pressure shadows around the rigid grains that can resist tectonic extrusion and protect some organic pores. LPGA experiment results also show that micropore-specific surface areas and pore volumes of the samples with strong deformation are larger than those with weak deformation. The shale samples with strong deformation also have more microchannels and microfractures. Tectonism can also cause some micropores to become macropores; for example, tectonism can cause the rigid grains to slide and rotate, enlarging the dissolution pores at the edges of rigid grains. Shale samples with strong deformation have a smaller mesopore volume; but due to the presence of organic-clay aggregates, a larger mesopore-specific surface area embarks on these samples. According to fractal dimension calculations, it is found that in strong deformed shale, more multiple dimensions of the pore system tend to represent rougher pore surfaces and more irregular shapes. Besides, rougher pore surfaces are eager to provide more adsorption sites and enhance the adsorption capacity of the deformed shale. This study investigates the relationship between tectonism and composition and pore characteristics of shale reservoirs and may promote understanding of the accumulation of shale gas in highly deformed areas.

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“…[16][17][18][19][20][21] In addition to its applicability for pore size distribution, pore surface area and pore volume determination, researchers have combined fractal dimension analysis with adsorption isotherms to obtain more information from the pores. [22][23][24][25][26] Based on the literature, nearly all the authors utilized the FHH model solely to characterize fractal dimensions of shale rocks without any strong basis. Thus, to date, the following questions have remained unanswered: is the FHH model the most suitable one for fractal dimension analysis of shale rocks?…”

Section: Introductionmentioning

confidence: 99%

Comparison of fractal dimensions from nitrogen adsorption data in shale via different models

et al. 2021

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Organic nanopore structure and fractal characteristics of Wufeng and lower member of Longmaxi shales in southeastern Sichuan, China

Cited by 61 publications

References 49 publications

Composition Effect on the Pore Structure of Transitional Shale: A Case Study of the Permian Shanxi Formation in the Daning–Jixian Block at the Eastern Margin of the Ordos Basin

Composition Effect on the Pore Structure of Transitional Shale: A Case Study of the Permian Shanxi Formation in the Daning–Jixian Block at the Eastern Margin of the Ordos Basin

Relationship between Tectonism and Composition and Pore Characteristics of Shale Reservoirs

Comparison of fractal dimensions from nitrogen adsorption data in shale via different models

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