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

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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Geometric pore surface area and fractal dimension of catalyzed electrodes in polymer electrolyte membrane fuel cells

International Journal of Energy Research ◽

10.1002/er.4260 ◽

2018 ◽

Vol 43 (7) ◽

pp. 3011-3019 ◽

Cited By ~ 3

Author(s):

Jian Zhao ◽

Samaneh Shahgaldi ◽

Adnan Ozden ◽

Ibrahim E. Alaefour ◽

Xianguo Li ◽

...

Keyword(s):

Fractal Dimension ◽

Fuel Cells ◽

Polymer Electrolyte ◽

Surface Area ◽

Polymer Electrolyte Membrane ◽

Pore Surface ◽

Electrolyte Membrane ◽

Pore Surface Area

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Effect of peat mire evolution on pore structure characteristics in thick coal seam: Examples from Xishanyao Formation (Middle Jurassic), Yili Basin, China

Energy Exploration & Exploitation ◽

10.1177/0144598720950479 ◽

2020 ◽

Vol 38 (5) ◽

pp. 1484-1514 ◽

Cited By ~ 1

Author(s):

Rongfang Qin ◽

Anmin Wang ◽

Daiyong Cao ◽

Yingchun Wei ◽

Liqi Ding ◽

...

Keyword(s):

Fractal Dimension ◽

Coal Seam ◽

Specific Surface ◽

Pore Structure ◽

Surface Area ◽

Specific Surface Area ◽

Pore Volume ◽

Thick Coal Seam ◽

Structure Characteristics ◽

Cyclic Changes

The physical properties of thick coal seams show strong vertical heterogeneity; thus, an accurate characterization of their pore structure is essential for coalbed methane (CBM) exploration and production. A total of 18 coal samples, collected from a thick coal seam in the Yili Basin of NW China, were tested by a series of laboratory experiments to investigate the peat mire evolution and pore structure characteristics. The results show that the No. 4 coal seam has undergone multiple stages of evolution in the peatification stage, and was divided into four water-transgression/water-regression cycles according to the regular cyclic changes of the vitrinite/inertinite ratio, structure preservation index, gelification index, vegetation index, trace element ratios, and stable carbon isotopes of organic matter. The changes of pore structure characteristics with the changes of coal deposition cycles are also analyzed. It is concluded that pore structure characteristics of the four cycles are quite different. In each water-transgression cycle, the vitrinite gradually increased and the inertinite gradually decreased, resulting in a decrease of the porosity, pore volume, specific surface area, and fractal dimension. While in each water-regression cycle, the vitrinite gradually decreased and the inertinite gradually increased, leading to an increase of the porosity, pore volume, specific surface area, and fractal dimension. A strong relationship exists between the porosity, pore volume, specific surface area, fractal dimension, and submacerals, with fusinite and semifusinite which contained more pores having a positive correlation, desmocollinite and corpovitrinite which contained few pores having a negative correlation.

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The role of the pore surface area/pore volume ratio in chemical vapor infiltration

Journal de Physique IV (Proceedings) ◽

10.1051/jp4:1999809 ◽

1999 ◽

Vol 09 (PR8) ◽

pp. Pr8-73-Pr8-77 ◽

Cited By ~ 1

Author(s):

W. Benzinger ◽

K. J. Hüttinger

Keyword(s):

Surface Area ◽

Pore Volume ◽

Volume Ratio ◽

Chemical Vapor ◽

Chemical Vapor Infiltration ◽

Pore Surface ◽

Pore Surface Area ◽

Vapor Infiltration

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FRACTAL PARAMETERS OF SOIL PORE SURFACE AREA UNDER A DEVELOPING CROP

Fractals ◽

10.1142/s0218348x96000121 ◽

1996 ◽

Vol 04 (01) ◽

pp. 97-104 ◽

Cited By ~ 10

Author(s):

YA. A. PACHEPSKY ◽

L. P. KORSUNSKAIA ◽

M. HAJNOS

Keyword(s):

Fractal Dimension ◽

Surface Area ◽

Plant Development ◽

Fractal Dimensions ◽

Carbohydrate Oxidation ◽

Surface Irregularity ◽

Pore Surface ◽

Cutoff Values ◽

Fractal Parameters ◽

Pore Surface Area

Fractal parameters of soils has become increasingly important in understanding and quantifying transport and adsorption phenomena in soils. It is not known how soil plant development may affect fractal characteristics of soil pores. We estimated pore surface area fractal parameters from mercury porosimetry data on gray forest soil before and during crop development, in samples both containing and not containing soil carbohydrates known to be important structure-forming agents. Two distinct intervals with different fractal dimensions were found in the range of pore radii from 4 nm to 1 μm. This could be attributed to differences in mineral composition of soil particles of different sizes. The interval of the smallest radii had the highest average fractal dimension close to 3. Smaller surface area fractal dimensions corresponding to low surface irregularity were found in the next interval of radii. The plant development affected neither fractal dimensions nor the cutoff values of soil samples. The carbohydrate oxidation caused a significant increase in the fractal dimension in the interval of larger radii, but did not affect fractal dimension in the interval of small radii. The cutoff values decreased after carbohydrate oxidation.

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Nano-Scale Pore Structure and Its Multi-Fractal Characteristics of Tight Sandstone by N2 Adsorption/Desorption Analyses: A Case Study of Shihezi Formation from the Sulige Gas Filed, Ordos Basin, China

Minerals ◽

10.3390/min10040377 ◽

2020 ◽

Vol 10 (4) ◽

pp. 377

Author(s):

Zhelin Wang ◽

Xuewei Jiang ◽

Mao Pan ◽

Yongmin Shi

Keyword(s):

Fractal Dimension ◽

Specific Surface ◽

Pore Structure ◽

Surface Area ◽

Mineral Composition ◽

Fractal Dimensions ◽

Contribution Rate ◽

Tight Sandstone ◽

N2 Adsorption ◽

Adsorption Desorption

Fractal dimension is a critical parameter to evaluate the heterogeneity of complex pore structure in tight sandstone gas and other low permeability reservoirs. To quantify the fractal dimension of tight sandstone at various pore size classes and evaluate their implications on mineral composition and nano pore structure parameters, we conducted an integrated approach of N2 adsorption/desorption experiment (N2-GA), X-ray diffraction (X-RD), and field emission scanning electron microscopy (FE-SEM) on Sulige tight sandstone reservoirs. By comparing the nine types of fractal dimensions calculated from N2 adsorption data, we put forward the concept of “concentrated” fractal dimensions and “scattered” fractal dimensions (DN2, DN3, DN5, DN7 and DN8) for the first time according to its concentration extent of distribute in different samples. Result shows that mineral composition has a significant influence of a different level on specific surface area (SSA), pore volume (PV), and fractal dimensions (DN), respectively, where the “scattered” fractal dimension is more sensitive to certain specific property of the reservoir, including mineral content and the specific surface area contribution rate (Sr) of type II mesopores (Mesopore-II: 10~50nm). In addition, three type of hysteresis loops were distinguished corresponding to different pore shape combination of N2-GA isotherm curve, which reveals that pore structure heterogeneity is mainly controlled by inkbottle-shaped pores and the volume contribution rate (Vr) of mesopores in this study area. These findings could contribute to a better understanding of the controlling effect of pore heterogeneity on natural gas storage and adsorption.

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Nanometer Pore Structure Characterization of Taiyuan Formation Shale in the Lin-Xing Area Based on Nitrogen Adsorption Experiments

Minerals ◽

10.3390/min11030298 ◽

2021 ◽

Vol 11 (3) ◽

pp. 298

Author(s):

Chenlong Ding ◽

Jinxian He ◽

Hongchen Wu ◽

Xiaoli Zhang

Keyword(s):

Specific Surface ◽

Pore Structure ◽

Surface Area ◽

Specific Surface Area ◽

Shale Gas ◽

Pore Volume ◽

Ordos Basin ◽

Total Pore Volume ◽

Nitrogen Adsorption ◽

Taiyuan Formation

Ordos Basin is an important continental shale gas exploration site in China. The micropore structure of the shale reservoir is of great importance for shale gas evaluation. The Taiyuan Formation of the lower Permian is the main exploration interval for this area. To examine the nanometer pore structures in the Taiyuan Formation shale reservoirs in the Lin-Xing area, Northern Shaanxi, the microscopic pore structure characteristics were analyzed via nitrogen adsorption experiments. The pore structure parameters, such as specific surface area, pore volume, and aperture distribution, of shale were calculated; the significance of the pore structure for shale gas storage was analyzed; and the main controlling factors of pore development were assessed. The results indicated the surface area and hole volume of the shale sample to be 0.141–2.188 m2/g and 0.001398–0.008718 cm3/g, respectively. According to the IUPAC (International Union of Pure and Applied Chemistry) classification, mesopores and macropores were dominant in the pore structure, with the presence of a certain number of micropores. The adsorption curves were similar to the standard IV (a)-type isotherm line, and the hysteresis loop type was mainly similar to H3 and H4 types, indicating that most pores are dominated by open type pores, such as parallel plate-shaped pores and wedge-shaped slit pores. The micropores and mesopores provide the vast majority of the specific surface area, functioning as the main area for the adsorption of gas in the shale. The mesopores and macropores provide the vast majority of the pore volume, functioning as the main storage areas for the gas in the shale. Total organic carbon had no notable linear correlation with the total pore volume and the specific surface area. Vitrinite reflectance (Ro) had no notable correlation with the specific surface area, but did have a low “U” curve correlation with the total pore volume. There was no relationship between the quartz content and specific surface area and total pore volume. In addition, there was no notable correlation between the clay mineral content and total specific surface area and total pore volume.

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Investigation of the methane adsorption characteristics of marine organic-rich shale: A case study of the lower Cambrian Niutitang Shale in the Fenggang block, northern Guizhou Province, South China

Interpretation ◽

10.1190/int-2017-0238.1 ◽

2018 ◽

Vol 6 (4) ◽

pp. T819-T833 ◽

Cited By ~ 3

Author(s):

Yang Gu ◽

Wenlong Ding ◽

Min Yin ◽

Ruyue Wang ◽

Baocheng Jiao ◽

...

Keyword(s):

Specific Surface ◽

Pore Size ◽

Adsorption Capacity ◽

Surface Area ◽

South China ◽

Pore Volume ◽

Lower Cambrian ◽

Methane Adsorption ◽

Guizhou Province ◽

Average Value

The marine shale in South China has great gas exploration potential, and exploration in the Sichuan Basin has been successful, but the degree of exploration remains low in the Guizhou Province. We used organic geochemical analyses (total organic carbon content and kerogen type), scanning electron microscopy (SEM), field emission SEM, nuclear magnetic resonance (NMR), X-ray diffraction analysis, and low-temperature [Formula: see text] and [Formula: see text] adsorption experimental methods to study the micropore types and pore structures and their effects on the methane adsorption capacity of organic-rich shales found in the Fenggang block in northern Guizhou Province. The results indicate that the microscopic surface porosity of the lower Cambrian Niutitang Formation ranges from 2.88% to 5.34%, with an average value of 3.86%. Based on nitrogen adsorption methods, the range of the average pore size distribution is 4.6–9.491 nm, with an average value of 6.68 nm. All of the samples exhibit significant unimodal distributions. The main pore size is less than 10 nm, and these pores account for most of the mesopore volume, which is generally consistent with the NMR results. The methane adsorption capacity of the shale samples gradually increases in the range of 0–8 MPa at 30°C and reaches a maximum at approximately 10 MPa. Positive correlations were found between the gas content and specific surface area, total pore volume, and micropore volume. These strong correlations indicate that the Niutitang Shale has a high specific surface area, a high pore volume, and narrow-diameter pores, demonstrating that it has a high gas adsorption capacity. The results of this study provide valuable information regarding the adsorption characteristics of marine shales and the factors that affect those characteristics.

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Micropore Structure and Fractal Characteristics of Low-Permeability Coal Seams

Advances in Materials Science and Engineering ◽

10.1155/2018/4186280 ◽

2018 ◽

Vol 2018 ◽

pp. 1-15 ◽

Cited By ~ 2

Author(s):

Guang-zhe Deng ◽

Rui Zheng

Keyword(s):

Fractal Dimension ◽

Electron Microscope ◽

Scanning Electron Microscope ◽

Coal Seam ◽

Linear Relationship ◽

Surface Area ◽

Pore Volume ◽

Low Permeability ◽

Coal Seams ◽

Scanning Electron

With the raw coal from a typical low-permeability coal seam in the coalfield of South Junger Basin in Xinjiang as the research object, this paper examined six kinds of coal samples with different permeabilities using a scanning electron microscope and a low-temperature nitrogen adsorption test that employed a JSM-6460LV high-resolution scanning electron microscope and an ASAP2020 automatic specific surface area micropore analyzer to measure all characteristic micropore structural parameters. According to fractal geometry theory, four fractal dimension calculation models of coal and rock were established, after which the pore structure characteristic parameters were used to calculate the fractal dimensions of the different coal seams. The results show that (1) the low-permeability coal seam in the coalfield of South Junger Basin in Xinjiang belongs to mesoporous medium, with a certain number of large pores and no micropores. The varying adsorption capacities of the different coal seams were positively correlated with pore volume, surface area, and the mesoporous surface area proportions, from which it was concluded that mesopores were the main contributors to pore adsorption in low-permeability coal seams. (2) The raw coal pore fractal dimension had a negative linear relationship to average pore size, a positive linear relationship with total pore volume, total surface area, and adsorption capacity, and a positive correlation with the mesoporous surface area proportion; that is, the higher the fractal dimension, the larger the pore volume and surface area of the raw coal. (3) The permeability of the low-permeability coal seam had a phase correlation with the micropore development degree; that is, the permeability had a phase negative correlation with the pore distribution fractal dimension, and there was a positive correlation between permeability and porosity. These results are of theoretical significance for the clean exploitation of low-permeability coal seam resources.

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Evolution characteristics and model of nanopore structure and adsorption capacity in organic-rich shale during artificial thermal maturation: A pyrolysis study of the Mesoproterozoic Xiamaling marine shale with type II kerogen from Zhangjiakou, Hebei, China

Energy Exploration & Exploitation ◽

10.1177/0144598718810256 ◽

2018 ◽

Vol 37 (1) ◽

pp. 493-518 ◽

Cited By ~ 2

Author(s):

Liangwei Xu ◽

Yang Wang ◽

Luofu Liu ◽

Lei Chen ◽

Ji Chen

Keyword(s):

Pore Structure ◽

Adsorption Capacity ◽

Surface Area ◽

Pore Volume ◽

Oil Shale ◽

Hydrocarbon Generation ◽

Type Ii ◽

Thermal Maturation ◽

Evolution Characteristics ◽

Nanopore Structure

Thermal maturity has a considerable impact on hydrocarbon generation, mineral conversion, nanopore structure, and adsorption capacity evolution of shale, but that impact on organic-rich marine shales containing type II kerogen has been rarely subjected to explicit and quantitative characterization. This study aims to obtain information regarding the effects of thermal maturation on organic matter, mineral content, pore structure, and adsorption capacity evolution of marine shale. Mesoproterozoic Xiamaling immaturity marine oil shale with type II kerogen in Zhangjiakou of Hebei, China, was chosen for anhydrous pyrolysis to simulate the maturation process. With increasing simulation temperature, hydrocarbon generation and mineral transformation promote the formation, development, and evolution of pores in the shale. The original and simulated samples consist of closed microspores and one-end closed pores of the slit throat, all-opened wedge-shaped capillaries, and fractured or lamellar pores, which are related to the plate particles of clay. The increase in maturity can promote the formation and development of pores in the shale. Heating can also promote the accumulation, formation, and development of pores, leading to a large pore volume and surface area. The temperature increase can promote the development of pore volume and surface area of 1–10 and 40-nm diameter pores. The formation and development of pore volume and surface area of 1–10 nm diameter pores are more substantial than that of 40-nm diameter pores. The pore structure evolution of the sample can be divided into pore adjustment (T < 350°C, EqRo < 0.86%), development (350°C < T < 650°C, 0.86% < EqRo < 3.28%), and conversion or destruction stages (T > 650°C, EqRo > 3.28%). Along with the increase in maturity, the methane adsorption content decreases in the initial simulation stage, increases in the middle simulation stage, and reaches the maximum value at 650°C, after which it gradually decreases. A general evolution model is proposed by combining the nanopore structure and the adsorption capacity evolution characteristics of the oil shale.

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