The composition, pore structure characterization and deformation mechanism of coal-bearing shales from tectonically altered coalfields in eastern China

Ju, Yi‐Hsu; Sun, Ying; Tan, Jingqiang; Bu, Hongling; Han, Kui; Li, Xiaoshi; Fang, Lizhi

doi:10.1016/j.fuel.2018.06.116

Cited by 125 publications

(64 citation statements)

References 39 publications

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“…Some scholars believe that tectonic stress will cause the reduction of pores; that is, as the tectonism increases, the degree of pore reduction will increase, especially for mesopores and macropores [4,23]. However, it is argued among experts that the tectonism can also produce the cleavage domains and increase the pore volume and specific surface area [32,36]. Ma et al found that the Lujiaping shale developed three-dimensional connected pore systems composed of nanometer-sized intergranular pore spaces, aggregate pore spaces in clay flakes, and a pore network in the cleavage domains, which provides the main specific surface area and adsorption point [32].…”

Section: Introductionmentioning

confidence: 99%

“…Recently, some researchers have got down to notice natural tectonic deformed samples and conducted experiments to study the relationship between tectonism and shale composition and pore structure features through experiments [32,[36][37][38][39][40]. Ju et al made inner comparison among the material composition and pore characteristics of brittle deformation, ductile deformation, and brittleductile shale samples from various areas and found that brittle shear results in microfractures and large pores and thus has an impact on the desorption and percolation capability of shale gas; the ductile deformation increased the specific surface area and enhanced the adsorption capacity of deformed shale [36]. Liang et al found that the tectonism has little effect on shale mineral composition, maturity, porosity, and total pore volume by comparing the deformed sample with the undeformed sample but has a great influence on specific surface area, adsorption capacity, and pore size distribution [38].…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Relationship between Tectonism and Composition and Pore Characteristics of Shale Reservoirs

et al. 2020

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“…From the Precambrian to Tertiary periods, organic-rich shale deposited in marine, transitional marine, or lacustrine settings, and is widely distributed in China [11]. Related researches have expounded the depositional environment, geochemical and reservoir characteristics, gas concentration, and prospective resource potential of the three different types of shale in China [12][13][14][15][16]. The Upper Yangtze Platform, where the Sichuan Basin is located, is one of the largest conventional natural gas provinces of China.…”

Section: Introductionmentioning

confidence: 99%

Nano-Scale Pore Structure and Fractal Dimension of Longmaxi Shale in the Upper Yangtze Region, South China: A Case Study of the Laifeng–Xianfeng Block Using HIM and N2 Adsorption

Huang

Zhu

et al. 2019

Minerals

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This paper tries to determine the key evaluation parameters of shale reservoirs in the complex tectonic provinces outside the Sichuan Basin in South China, and also to target the sweet spots of shale reservoirs accurately. The pore-structure characteristics of the Lower Silurian Longmaxi shale gas reservoirs in Well LD1 of the Laifeng–Xianfeng Block, Upper Yangtze region, were evaluated. N2 adsorption and helium ion microscope (HIM) were used to investigate the pore features including pore volume, pore surface area, and pore size distribution. The calculated results show good hydrocarbon storage capacity and development potential of the shale samples. Meanwhile, the reservoir space and migration pathways may be affected by the small pore size. As the main carrier of pores in shale, organic matter contributes significantly to the pore volume and surface area. Samples with higher total organic carbon (TOC) content generally have higher porosity. Based on the Frenkel–Halsey–Hill equation (FHH model), two different fractal dimensions, D1 and D2, were observed through the N2 adsorption experiment. By analyzing the data, we found that large pores usually have large values of fractal dimension, owing to their complex pore structure and rough surface. In addition, there exists a good positive correlation between fractal dimension and pore volume as well as pore surface area. The fractal dimension can be taken as a visual indicator that represents the degree of development of the pore structure in shale.

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“…The contribution of thermogenic, OM-hosted nanopores to overall porosity is such that organic porosity can be as high as 40% of total porosity [19][20][21][22][23][24]. However, recent studies have suggested that organic porosity in naturally deformed shales are poorly developed, and that fractured-related and mineral-hosted pores are more widely recognized as being the most significant components of porosity in naturally deformed shales [25][26][27]. The discovery of mineral-hosted and fracture-related pore systems in naturally deformed shales sparked many questions concerning their characteristics, prediction, and reservoir quality: (1) Are such pore networks primary (hosted within initially particles and shale matrix) versus secondary (formed during tectonic deformation)?…”

Section: Introductionmentioning

confidence: 99%

Tectonic and Thermal Controls on the Nano-Micro Structural Characteristic in a Cambrian Organic-Rich Shale

Zhu

Huang

et al. 2019

Minerals

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Until recently, the characteristics of nano-microscale structures in the naturally deformed, overmature, marine shales were poorly known. Thermally overmature Lujiaping shales in the complex tectonic area of the northeast part of the upper Yangtze area, China have experienced strong tectonic deformation and are considered as potentially important strata for shale gas exploration. Naturally deformed samples from the main source rocks are selected from the Lower Cambrian Lujiaping Formation in the Dabashan Thrust-fold Belt to investigate nanometer- to micrometer-sized structures. A combination of scanning electron microscope (SEM), low-pressure nitrogen adsorption (LPNA), and low-field nuclear magnetic resonance (NMR) suggests that the pore types are dominantly fracture-related pores with a lesser abundance of mineral-hosted pores. These two pore types account for the 90% of total pore space. Organic matter (OM)-hosted pores are rare and make up a small part of the pore systems (less than 10%) due to high thermal maturity and intensive tectonic compression. Overall, the Lujiaping deformed, overmature samples have abundant nanometer- to micrometer-sized inorganic pores. High-resolution SEM images provide direct evidence of the formation of nano- and microsized structures such as OM–clay aggregates and silica nanograins. OM–clay aggregates are commonly observed in samples, which also exhibit abundant open microfractures and interparticle pores. Quartz can occur as silica nanograins and botryoids typically 20–100 nm in size, which may influence porosity through the creation or occupying interparticle pore space.

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The composition, pore structure characterization and deformation mechanism of coal-bearing shales from tectonically altered coalfields in eastern China

Cited by 125 publications

References 39 publications

Relationship between Tectonism and Composition and Pore Characteristics of Shale Reservoirs

Relationship between Tectonism and Composition and Pore Characteristics of Shale Reservoirs

Nano-Scale Pore Structure and Fractal Dimension of Longmaxi Shale in the Upper Yangtze Region, South China: A Case Study of the Laifeng–Xianfeng Block Using HIM and N2 Adsorption

Tectonic and Thermal Controls on the Nano-Micro Structural Characteristic in a Cambrian Organic-Rich Shale

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