Fractal characteristics of pore structures in 13 coal specimens: Relationship among fractal dimension, pore structure parameter, and slurry ability of coal

In this study, a series of nuclear magnetic resonance (NMR) tests was conducted on calcareous sand, quartz sand, and glass bead with a wide range of grain sizes, to understand the effect of grain size on the micro-pore structure and fractal characteristics of the carbonate-based sand and silicate-based sand. The pore size distribution (PSD) of the tested materials were obtained from the NMR T2 spectra, and fractal theory was introduced to describe the fractal properties of PSD. Results demonstrate that grain size has a significant effect on the PSD of carbonate-based sand and silicate-based sand. As grain size increases, the PSD of sands evolves from a binary structure with two peaks to a ternary structure with three peaks. The increase in the grain size can cause a remarkable increase in the maximum pore size. It is also found that the more irregular the particle shape, the better the continuity between the large and medium pores. In addition, grain size has a considerable effect on the fractal dimension of the micro-pore structure. The increase of grain size can lead to a significant increase in the heterogeneity and fractal dimension in PSD for calcareous sand, quartz sand and glass bead.

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The Impacts of Matrix Compositions on Nanopore Structure and Fractal Characteristics of Lacustrine Shales from the Changling Fault Depression, Songliao Basin, China

Minerals ◽

10.3390/min9020127 ◽

2019 ◽

Vol 9 (2) ◽

pp. 127 ◽

Cited By ~ 6

Author(s):

Zhuo Li ◽

Zhikai Liang ◽

Zhenxue Jiang ◽

Fenglin Gao ◽

Yinghan Zhang ◽

...

Keyword(s):

Fractal Dimension ◽

Pore Structure ◽

Fractal Dimensions ◽

Organic Medium ◽

Songliao Basin ◽

Sem Images ◽

Fractal Characteristics ◽

Inorganic Mineral ◽

Nanopore Structure ◽

High Fractal Dimension

The Lower Cretaceous Shahezi shales are the targets for lacustrine shale gas exploration in Changling Fault Depression (CFD), Southern Songliao Basin. In this study, the Shahezi shales were investigated to further understand the impacts of rock compositions, including organic matters and minerals on pore structure and fractal characteristics. An integrated experiment procedure, including total organic carbon (TOC) content, X-ray diffraction (XRD), field emission-scanning electron microscope (FE-SEM), low pressure nitrogen physisorption (LPNP), and mercury intrusion capillary pressure (MICP), was conducted. Seven lithofacies can be identified according to on a mineralogy-based classification scheme for shales. Inorganic mineral hosted pores are the most abundant pore type, while relatively few organic matter (OM) pores are observed in FE-SEM images of the Shahezi shales. Multimodal pore size distribution characteristics were shown in pore width ranges of 0.5–0.9 nm, 3–6 nm, and 10–40 nm. The primary controlling factors for pore structure in Shahezi shales are clay minerals rather than OM. Organic-medium mixed shale (OMMS) has the highest total pore volumes (0.0353 mL/g), followed by organic-rich mixed shale (ORMS) (0.02369 mL/g), while the organic-poor shale (OPS) has the lowest pore volumes of 0.0122 mL/g. Fractal dimensions D1 and D2 (at relative pressures of 0–0.5 and 0.5–1 of LPNP isotherms) were obtained using the Frenkel–Halsey–Hill (FHH) method, with D1 ranging from 2.0336 to 2.5957, and D2 between 2.5779 and 2.8821. Fractal dimensions are associated with specific lithofacies, because each lithofacies has a distinctive composition. Organic-medium argillaceous shale (OMAS), rich in clay, have comparatively high fractal dimension D1. In addition, organic-medium argillaceous shale (ORAS), rich in TOC, have comparatively high fractal dimension D2. OPS shale contains more siliceous and less TOC, with the lowest D1 and D2. Factor analysis indicates that clay contents is the most significant factor controlling the fractal dimensions of the lacustrine Shahezi shale.

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Micro-Nanopore Structure and Fractal Characteristics of Tight Sandstone Gas Reservoirs in the Eastern Ordos Basin, China

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2021.18743 ◽

2021 ◽

Vol 21 (1) ◽

pp. 234-245

Author(s):

Peng Qiao ◽

Yiwen Ju ◽

Jianchao Cai ◽

Jun Zhao ◽

Hongjian Zhu ◽

...

Keyword(s):

Fractal Dimension ◽

Pore Structure ◽

Ordos Basin ◽

Gas Storage ◽

Main Peak ◽

Storage Space ◽

Tight Sandstone ◽

Fractal Characteristics ◽

Sandstone Reservoirs ◽

Nanopore Structure

The complex pore system in tight sandstone reservoirs controls the storage and transport of natural gas. Thus, quantitatively characterizing the micro-nanopore structure of tight sandstone reservoirs is of great significance to determining the accumulation and distribution of tight gas. The pore structure of reservoirs was determined through polarizing microscopy, scanning electron microscopy (SEM), and the combination of mercury injection capillary pressure (MICP) and nuclear magnetic resonance (NMR) experiments on Late Paleozoic conventional and tight sandstone samples from the Linxing Block, Ordos Basin. The results show that in contrast to conventional sandstone, dissolution pores, with diameters less than 8 μm, are the main contributors to the gas storage space of tight sandstone reservoirs. The pore size distribution derived from the MICP experiment demonstrates that the main peak of tight sandstones corresponds to a pore radius in the range of 247 nm to 371 nm, while the secondary peak usually corresponds to 18 nm. The results of the NMR test illustrate that the T2 spectra of tight sandstones are unimodal, bimodal and multimodal, and the main NMR peak is highly related to the MICP peak. Fractal theory was proposed to quantitatively characterize the complex pore structure and rough porous surface. The sandstones show fractal characteristics including nanopore fractal dimension DN obtained from the MICP and large pore fractal dimension DL obtained from the NMR experiment. Both DN and DL are positively correlated with porosity and negatively correlated with permeability, demonstrating that complex and heterogeneous pore structure could increase the gas storage space and reduce the connectivity.

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Fractal analysis of pore structures in graphene oxide-carbon nanotube based cementitious pastes under different ultrasonication

Nanotechnology Reviews ◽

10.1515/ntrev-2019-0010 ◽

2019 ◽

Vol 8 (1) ◽

pp. 107-115 ◽

Cited By ~ 12

Author(s):

Yuan Gao ◽

Hongwen Jing ◽

Zefu Zhou

Keyword(s):

Graphene Oxide ◽

Fractal Dimension ◽

Pore Structure ◽

Pore Size ◽

Size Range ◽

Fractal Dimensions ◽

Pore Characteristics ◽

Pore Structures ◽

Cement Additive ◽

Multi Walled Carbon Nanotubes

Abstract Nano cement additive using a hybrid of graphene oxide (GO) and multi-walled carbon nanotubes (MWCNTs) combines the excellent affinity of GO and the superior mechanical properties of MWCNTs. Ultrasonication is the key process to disperse the GO/MWCNTs and further optimizes the pore structures of cement-based pastes. Fractal dimension can effectively and quantitatively characterize the pore structures of cementitious composites. The present study investigates the fractal dimensions of pore structures of GO/MWCNT-OPC pastes under power- and time-controlled ultrasonication based on the mercury intrusion porosimetry (MIP) tests data. The finding of this study shows that comparing to calculating the fractal dimension of the overall pore size range, assessing the variations of fractal dimension of individual pore size range is more effective in evaluating the pore characteristic. The fractal dimension of larger capillary pores $$\left( {{D}_{>{{10}^{4}}nm}} \right)$$can be use to describe the change of pore structure of GO/MWCNT-OPC pastes under ultrasonication treatment with sufficient accuracy as higher value of $${{D}_{>{{10}^{4}}nm}}$$indicates better pore characteristics. The fractal dimension change trend of mesopores is always opposite to that of bigger capillary pores. Modest increment in both power- and time-controlled ultrasonication seems to result in the increase of the fractal dimension of capillary pores and lead to better reinforcement effects. Prolongation of ultrasonication time slightly influences the pore structure of the specimens, while nano cement additives exposed to excess ultrasonication power fail to afford adequate reinforcing effect and finally cause the deterioration of the pore structures. The findings of this study can provide helpful information of GO/MWCNT-OPC pastes and ultrasonication treatment in the future.

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Nano-Pore Structure and Fractal Characteristics of Shale Gas Reservoirs: A Case Study of Longmaxi Formation in Southeastern Chongqing, China

Journal of Nanoscience and Nanotechnology ◽

10.1166/jnn.2021.18721 ◽

2021 ◽

Vol 21 (1) ◽

pp. 343-353

Author(s):

Wei-Dong Xie ◽

Meng Wang ◽

Xiao-Qi Wang ◽

Yan-Di Wang ◽

Chang-Qing Hu

Keyword(s):

Fractal Dimension ◽

Pore Structure ◽

Shale Gas ◽

Fractal Dimensions ◽

Gas Reservoirs ◽

Longmaxi Formation ◽

Shale Gas Reservoirs ◽

Fractal Characteristics ◽

Temperature Liquid ◽

Menger Sponge

Pore structure and fractal dimensions can characterize the adsorption, desorption and seepage characteristics of shale gas reservoirs. In this study, pore structure, fractal characteristics and influencing factors were studied of the Longmaxi formation shale gas reservoir in southeastern Chongqing, China. Scanning electron microscopy was used to describe the characteristics of various reservoirs. High pressure mercury intrusion and low temperature liquid N2 and CO2 adsorption experiments were used to obtain pore structure parameters. V–S model, FHH model and Menger sponge model were selected to calculate the micropore, mesopore and macropore fractal dimensions, respectively. The results show that organic matter pores, inter-granular pores, intra-granular pores and micro-fractures are developed within the shale, and the pore morphology is mostly ink pores and parallel plate pores with aperture essentially in the 1–2 nm and 2–50 nm ranges. Moreover, macropores are the most complex in these samples, with mesopores being less complex than macropores, and the micropores being the simplest. D1 (micropore fractal dimension) ranges from 2.31 to 2.50, D2 (mesopore fractal dimension) ranges from 2.74 to 2.83, D3 (macropore fractal dimension) ranges from 2.87 to 2.95, and Dt (comprehensive fractal dimension) ranges from 2.69 to 2.83 of fractal characteristics. D1 and D2 are mainly controlled by TOC content, while D3 and Dt are mainly controlled by brittle and clay mineral content. These results may be helpful for exploration and the development of shale gas in southeastern Chongqing, China.

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An Investigation of Fractal Characteristics of Marine Shales in the Southern China from Nitrogen Adsorption Data

Journal of Chemistry ◽

10.1155/2015/303164 ◽

2015 ◽

Vol 2015 ◽

pp. 1-12 ◽

Cited By ~ 8

Author(s):

Jian Xiong ◽

Xiangjun Liu ◽

Lixi Liang

Keyword(s):

Fractal Dimension ◽

Pore Structure ◽

Southern China ◽

Fractal Dimensions ◽

Nitrogen Adsorption ◽

Mean Value ◽

Relative Pressure ◽

Pore Surface ◽

Adsorption Sites ◽

Fractal Characteristics

We mainly focus on the Permian, Lower Cambrian, Lower Silurian, and Upper Ordovician Formation; the fractal dimensions of marine shales in southern China were calculated using the FHH fractal model based on the low-pressure nitrogen adsorption analysis. The results show that the marine shales in southern China have the dual fractal characteristics. The fractal dimensionD1at low relative pressure represents the pore surface fractal characteristics, whereas the fractal dimensionD2at higher relative pressure describes the pore structure fractal characteristics. The fractal dimensionsD1range from 2.0918 to 2.718 with a mean value of 2.4762, and the fractal dimensionsD2range from 2.5842 to 2.9399 with a mean value of 2.8015. There are positive relationships between fractal dimensionD1and specific surface area and total pore volume, whereas the fractal dimensionsD2have negative correlation with average pore size. The larger the value of the fractal dimensionD1is, the rougher the pore surface is, which could provide more adsorption sites, leading to higher adsorption capacity for gas. The larger the value of the fractal dimensionD2is, the more complicated the pore structure is, resulting in the lower flow capacity for gas.

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Two-parameter prestack seismic inversion of porosity and pore structure parameter of fractured carbonate reservoirs: Part 1 — Methods

Interpretation ◽

10.1190/int-2017-0219.1 ◽

2018 ◽

Vol 6 (4) ◽

pp. SM1-SM8 ◽

Cited By ~ 1

Author(s):

Tingting Zhang ◽

Yuefeng Sun

Keyword(s):

Pore Structure ◽

Seismic Data ◽

Rock Physics ◽

Seismic Inversion ◽

High Porosity ◽

Structure Parameter ◽

Pore Structure Parameter ◽

Fractured Zones ◽

Physics Model ◽

Rock Physics Model

Fractured zones in deeply buried carbonate hills are important because they often have better permeability resulting in prolific production than similar low-porosity rocks. Nevertheless, their detection poses great challenge to conventional seismic inversion methods because they are mostly low in acoustic impedance and bulk modulus, hardly distinguishable from high-porosity zones or mudstones. A proxy parameter of pore structure defined in a rock-physics model, the so-called Sun model, has been used for delineating fractured zones in which the pore structure parameter is relatively high, whereas the porosity is low in general. Simultaneous seismic inversion of the pore structure parameter and porosity proves to be difficult and nontrivial in practice. Although the pore structure parameter is well-defined at locations where density, P-, and S-velocity are known from logs, estimation of P- and S-velocity information, especially density information from prestack seismic data is rather challenging. A three-step iterative inversion method, which uses acoustic, gradient, and elastic impedance from angle-stacked seismic data as input to the rock-physics model for calculating porosity and bulk and shear pore structure parameters simultaneously, is proposed and implemented to solve this problem. The methodology is successfully tested with well logs and seismic data from a deeply buried carbonate hill in the Bohai Bay Basin, China.

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Two-parameter prestack seismic inversion of porosity and pore-structure parameter of fractured carbonate reservoirs: Part 2 — Applications

Interpretation ◽

10.1190/int-2018-0019.1 ◽

2018 ◽

Vol 6 (4) ◽

pp. SM9-SM17 ◽

Cited By ~ 1

Author(s):

Tingting Zhang ◽

Ruifeng Zhang ◽

Jianzhang Tian ◽

Lifei Lu ◽

Fengqi Qin ◽

...

Keyword(s):

Pore Structure ◽

Rock Physics ◽

Seismic Inversion ◽

Carbonate Reservoirs ◽

Bohai Bay ◽

Fractured Reservoir ◽

Structure Parameter ◽

Pore Structure Parameter ◽

Buried Hill ◽

Prestack Seismic Inversion

Fractures and fracture-related dissolution pores, as well as cavities, molds, and vugs, provide the major conduit and/or storage space for hydrocarbons in the deeply buried carbonate hill of Hexiwu field, Bohai Bay Basin. The fractured reservoir generally has lower porosity but better permeability than moldic/vuggy reservoir, and it consists of the major part of the buried-hill slope and buried-hill internal reservoirs. The conventional method of characterizing carbonate reservoirs, however, often mixes these two types of reservoirs together because they both have low acoustic impedance and low bulk modulus. The rock-physics analysis of two field wells indicates that a pore-structure parameter defined in a rock-physics model, the so-called Sun model, can help to distinguish the fractured reservoir zones together with porosity. Fractured zones usually have porosity of less than 5% and a pore-structure parameter of greater than six, whereas moldic/vuggy reservoirs of higher porosity have a pore-structure parameter of less than six. Field-scale application demonstrates that simultaneous prestack seismic inversion for the porosity and pore-structure parameter enables 3D mapping of fractured reservoir zones in the buried carbonate hills. It also provides an analog of detecting fractures and/or fracture-related pores in deeply buried carbonates in similar geologic settings.

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Relationship between pore structure and permeability of hardened cement mortars: On the choice of effective pore structure parameter

Cement and Concrete Research ◽

10.1016/s0008-8846(97)00111-7 ◽

1997 ◽

Vol 27 (8) ◽

pp. 1225-1235 ◽

Cited By ~ 48

Author(s):

L'. Bágel' ◽

V. Živica

Keyword(s):

Pore Structure ◽

Hardened Cement ◽

Structure Parameter ◽

Pore Structure Parameter ◽

Cement Mortars

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Strength and Transport Properties of Concretes Modified with Coarse Limestone Powder to Compensate for Dilution Effects

Transportation Research Record Journal of the Transportation Research Board ◽

10.3141/2290-17 ◽

2012 ◽

Vol 2290 (1) ◽

pp. 130-138 ◽

Cited By ~ 4

Author(s):

Narayanan Neithalath ◽

Hieu T. Cam

Keyword(s):

Pore Structure ◽

Silica Fume ◽

Dilution Effect ◽

Limestone Powder ◽

Structure Parameter ◽

Pore Structure Parameter ◽

Replacement Level ◽

Chloride Permeability ◽

Cement Replacement ◽

The Impact

The use of a coarse limestone powder (median particle size of approximately 70 μm, five times larger than cement particles) as a cement replacement material results in a dilution effect. The magnitude of strength and transport property reduction is found to be greater than the magnitude of the cement replacement level. In this paper, methodologies to proportion concrete containing 10% to 15% of coarse limestone powder, in which the dilution effect is compensated through a combination of reduction in water-to-powder ratio and addition of 5% of silica fume, are discussed. Limestone–silica fume blended concretes at a reduced water-to-powder ratio (0.37 or 0.34, depending on limestone replacement level) show similar or higher 56-day compressive strengths than does the benchmark plain concrete with a water-to-cement ratio of 0.40. The rapid chloride permeability and non–steady state migration values of the modified concretes are evaluated along with their pore structure parameter extracted from electrical impedance data. The impact of water-to-powder reduction and silica fume incorporation is quantified through this pore structure parameter.

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