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Fractal Fract
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Pore Structure and Fractal Characteristics in Unconventional Oil and Gas...
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Pore Structure and Fractal Characteristics in Unconventional Oil and Gas Reservoirs, 2nd Edition

A special issue of Fractal and Fractional (ISSN 2504-3110). This special issue belongs to the section "Engineering".

Deadline for manuscript submissions: 15 June 2026 | Viewed by 1502

Special Issue Editors

Dr. Zine El Abiddine Fellah

E-Mail Website
Guest Editor
Laboratory of Mechanics and Acoustics, French National Centre for Scientific Research LMA, CNRS, UMR 7031, Centrale Marseille, Aix-Marseille University CEDEX 20, F-13402 Marseille, France
Interests: porous materials; micropolar and fractal materials; fractional calculus; ultrasonic and low frequency characterization; acoustic propagation; vibroacoustic; alloys; direct and inverse problem solving; optimization
Special Issues, Collections and Topics in MDPI journals
Dr. Jizhen Zhang

E-Mail Website
Guest Editor
1. Key Laboratory of Exploration Technologies for Oil and Gas Resources, Ministry of Education, Yangtze University, Wuhan 430100, China
2. Laboratory of Reservoir Microstructure Evolution and Digital Characterization, Yangtze University, Wuhan 430100, China
Interests: pore structure; pore heterogeneity; complexity; fractal characteristics
Special Issues, Collections and Topics in MDPI journals
Dr. Quanzhong Guan

E-Mail Website
Guest Editor
Energy College, Chengdu University of Technology, Chengdu 610059, China
Interests: shale gas/oil; pore structure; pore heterogeneity; fractal characteristics; reservoir characteristics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Fractals possess self-similar patterns repeated at different scales and spatially. Many applications have been found for fractals, not only because of their beauty, which has itself received attention, but also because their governing rules simplify complex features in nature. The length and volume of a fractal are related to its characteristic size. Researchers have used fractals to model transport properties of porous media. There has been a growing interest in using fractals for understanding the transport properties of tight formations. Researchers have employed fractals to capture the heterogeneity of stimulated volume, complex geometries of fractures, and change in apparent and relative permeabilities. Fractals have found applications in analyzing the topology of the pore space. Researchers have used fractals to model transport properties of porous media. There has been a growing interest in using fractals for understanding the transport properties of tight formations. The pore structure and their fractal characteristics can have a significant effect on the spatial distributions of the wetting and nonwetting phases, occurrence, enrichment, and flow migration of unconventional oil and gas, which play a significant role in the theoretical research and exploration and development deployment of unconventional oil and gas resources.

In this Special Issue, “Pore Structure and Fractal Characteristics in Unconventional Oil and Gas Reservoirs, 2nd Edition", we would like to solicit your innovative ideas and work regarding the investigation and application of fractal dimensions in geological and geophysical science in the form of original articles. In addition, your study could focus on any aspect of geological and geophysical science, such as geological and geophysical material properties, numerical analysis, experimental and theoretical verifications, etc. The purpose of this Special Issue is to promote the deeper and wider investigation and application of fractal theory in fields of geological and geophysical science. Please note that manuscripts are required to utilize fractal theory, and should include fractal analysis or fractal applications. The submitted manuscripts will be peer reviewed, and those accepted will be published in the open access journal Fractal and Fractional. The topics to be considered in this Special Issue include, but are not limited to, the following:

  • Earth science;
  • Microstructures of shale, tight sandstone and coal;
  • Geotechnical engineering;
  • Engineering geology;
  • Granular aggregate properties;
  • Modelling of cracking behavior;
  • The impact of fractal characteristics on reservoirs;
  • Fractal characteristics of fractures;
  • Experimental and theoretical study.

Dr. Zine El Abiddine Fellah
Dr. Jizhen Zhang
Dr. Quanzhong Guan
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fractal and Fractional is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2700 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • pore structure
  • pore heterogeneity
  • complexity
  • fractal characteristics
  • microstructures
  • fractal cracks

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Related Special Issue

Published Papers (3 papers)

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Research

27 pages, 16665 KB  
Article
Microscopic Pore Structure Heterogeneity on the Breakthrough Pressure and Sealing Capacity of Carbonate Rocks: Insight from Monofractal and Multifractal Investigation
by Siqi Ouyang, Yiqian Qu, Yuting Cheng, Yupeng Wu and Xiuxiang Lü
Fractal Fract. 2025, 9(9), 589; https://doi.org/10.3390/fractalfract9090589 - 8 Sep 2025
Viewed by 303
Abstract
Reservoirs and caprocks overlap with each other in heterogeneous carbonate rocks. The sealing capacity of caprocks and their controlling factors are not clear, which restricts the prediction, exploration, and development of carbonate hydrocarbon reservoirs. We selected core samples from the Ordovician reservoirs and [...] Read more.
Reservoirs and caprocks overlap with each other in heterogeneous carbonate rocks. The sealing capacity of caprocks and their controlling factors are not clear, which restricts the prediction, exploration, and development of carbonate hydrocarbon reservoirs. We selected core samples from the Ordovician reservoirs and caprocks in the Tarim Basin, China, for scanning electron microscopy, thin section, breakthrough pressure (BP), high-pressure mercury intrusion porosimetry (HMIP), and nitrogen adsorption method (N2GA). The experimental results show that the reservoir and caprock can be distinguished by BP. The BP of the reservoir is less than 3.0 MPa, and the BP of the caprock is less than 3.0 Mpa. We analyzed the heterogeneity characteristics and differences in reservoirs and caprocks with different lithologies from the perspectives of monofractal and multifractal. The results indicate that the differences in pore structure of grainstone, dolomite, and micrite/argillaceous limestone result in significant heterogeneity differences between samples. The correlation analysis between the fractal parameters and BP indicates that the characteristics of reservoir microporous structures have a decisive impact on BP (correlation coefficient > 0.7). The pore structure of the carbonate reservoir–caprock system exhibits self-similarity. The heterogeneity of the caprock has no significant control effect on BP (correlation coefficient < 0.3), while the higher the heterogeneity of the reservoir, the greater the BP. The sealing capacity of the caprock depends on the heterogeneity differences in pore types and pore structures between the reservoirs and caprocks. When both the reservoir and the caprock are grainstone, the micropores in the reservoirs and caprocks are dispersed but evenly distributed, and little heterogeneous differences can achieve sealing. When the lithology of reservoirs and caprocks is different, the enhancement of heterogeneity differences in micropores will improve the sealing capacity of the caprock. In summary, fractal dimension is an effective method for studying the heterogeneous structure and sealing capacity of pore–throat in carbonate caprocks. This study proposes a new perspective that the difference between the heterogeneity of micropore structures of reservoirs and caprocks affects the sealing capacity of carbonate rocks, and provides a new explanation and model for the sealing mode of carbonate rock caprocks. Full article
(This article belongs to the Special Issue Pore Structure and Fractal Characteristics in Unconventional Oil and Gas Reservoirs, 2nd Edition)
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30 pages, 11585 KB  
Article
Multifractal Characterization of Marine Shale Pore Structure Alteration Induced by Supercritical CO2–Water–Rock Interaction
by Haonan Wei, Yi Du, Changqing Fu, Gaoqiang Fu, Yingfang Zhou, Jinfeng Ma, Zhenliang Wang, Zhejun Pan and Wei Gao
Fractal Fract. 2025, 9(9), 582; https://doi.org/10.3390/fractalfract9090582 - 2 Sep 2025
Viewed by 356
Abstract
Supercritical CO2 (ScCO2) injection has emerged as a promising method to enhance shale gas recovery while simultaneously achieving CO2 sequestration. This research investigates how ScCO2 interacts with water and shale rock, altering the pore structure characteristics of shale [...] Read more.
Supercritical CO2 (ScCO2) injection has emerged as a promising method to enhance shale gas recovery while simultaneously achieving CO2 sequestration. This research investigates how ScCO2 interacts with water and shale rock, altering the pore structure characteristics of shale reservoirs. The study examines shale samples from three marine shale formations in southern China under varying thermal and pressure regimes simulating burial conditions at 1000 m (45 °C and 10 MPa) and 2000 m (80 °C and 20 MPa). The research employs multiple analytical techniques including XRD for mineral composition analysis, MICP, N2GA, and CO2GA for comprehensive pore characterization, FE–SEM for visual observation of mineral and pore changes, and multifractal theory to analyze pore structure heterogeneity and connectivity. Key findings indicate that ScCO2–water–shale interactions lead to dissolution of minerals such as kaolinite, calcite, dolomite, and chlorite, and as the reaction proceeds, substantial secondary mineral precipitation occurs, with these changes being more pronounced under 2000 m simulation conditions. Mineral dissolution and precipitation cause changes in pore structure parameters of different pore sizes, with macropores showing increased PV and decreased SSA, mesopores showing decreased PV and SSA, and micropores showing insignificant changes. Moreover, mineral precipitation effects are stronger than dissolution effects. These changes in pore structure parameters lead to alterations in multifractal parameters, with mineral precipitation reducing pore connectivity and consequently enhancing pore heterogeneity. Correlation analysis further revealed that H and D−10–D10 exhibit a significant negative correlation, confirming that reduced connectivity corresponds to stronger heterogeneity, while mineral composition strongly controls the multifractal responses of macropores and mesopores, with micropores mainly undergoing morphological changes. However, these changes in micropores are mainly manifested as modifications of internal space. Siliceous shale samples exhibit stronger structural stability compared to argillaceous shale, which is attributed to the mechanical strength of the quartz framework. By integrating multifractal theory with multi–scale pore characterization, this study achieves a unified quantification of shale pore heterogeneity and connectivity under ScCO2–water interactions at reservoir–representative pressure–temperature conditions. This novelty not only advances the methodological framework but also provides critical support for understanding CO2–enhanced shale gas recovery mechanisms and CO2 geological sequestration in depleted shale gas reservoirs, highlighting the complex coupling between geochemical reactions and pore structure evolution. Full article
(This article belongs to the Special Issue Pore Structure and Fractal Characteristics in Unconventional Oil and Gas Reservoirs, 2nd Edition)
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20 pages, 11478 KB  
Article
Pore Evolution and Fractal Characteristics of Marine Shale: A Case Study of the Silurian Longmaxi Formation Shale in the Sichuan Basin
by Hongzhan Zhuang, Yuqiang Jiang, Quanzhong Guan, Xingping Yin and Yifan Gu
Fractal Fract. 2025, 9(8), 492; https://doi.org/10.3390/fractalfract9080492 - 28 Jul 2025
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Abstract
The Silurian marine shale in the Sichuan Basin is currently the main reservoir for shale gas reserves and production in China. This study investigates the reservoir evolution of the Silurian marine shale based on fractal dimension, quantifying the complexity and heterogeneity of the [...] Read more.
The Silurian marine shale in the Sichuan Basin is currently the main reservoir for shale gas reserves and production in China. This study investigates the reservoir evolution of the Silurian marine shale based on fractal dimension, quantifying the complexity and heterogeneity of the shale’s pore structure. Physical simulation experiments were conducted on field-collected shale samples, revealing the evolution of total organic carbon, mineral composition, porosity, and micro-fractures. The fractal dimension of shale pore was characterized using the Frenkel–Halsey–Hill and capillary bundle models. The relationships among shale components, porosity, and fractal dimensions were investigated through a correlation analysis and a principal component analysis. A comprehensive evolution model for porosity and micro-fractures was established. The evolution of mineral composition indicates a gradual increase in quartz content, accompanied by a decline in clay, feldspar, and carbonate minerals. The thermal evolution of organic matter is characterized by the formation of organic pores and shrinkage fractures on the surface of kerogen. Retained hydrocarbons undergo cracking in the late stages of thermal evolution, resulting in the formation of numerous nanometer-scale organic pores. The evolution of inorganic minerals is represented by compaction, dissolution, and the transformation of clay minerals. Throughout the simulation, porosity evolution exhibited distinct stages of rapid decline, notable increase, and relative stabilization. Both pore volume and specific surface area exhibit a trend of decreasing initially and then increasing during thermal evolution. However, pore volume slowly decreases after reaching its peak in the late overmature stage. Fractal dimensions derived from the Frenkel–Halsey–Hill model indicate that the surface roughness of pores (D1) in organic-rich shale is generally lower than the complexity of their internal structures (D2) across different maturity levels. Additionally, the average fractal dimension calculated based on the capillary bundle model is higher, suggesting that larger pores exhibit more complex structures. The correlation matrix indicates a co-evolution relationship between shale components and pore structure. Principal component analysis results show a close relationship between the porosity of inorganic pores, microfractures, and fractal dimension D2. The porosity of organic pores, the pore volume and specific surface area of the main pore size are closely related to fractal dimension D1. D1 serves as an indicator of pore development extent and characterizes the changes in components that are “consumed” or “generated” during the evolution process. Based on mineral composition, fractal dimensions, and pore structure evolution, a comprehensive model describing the evolution of pores and fractal dimensions in organic-rich shale was established. Full article
(This article belongs to the Special Issue Pore Structure and Fractal Characteristics in Unconventional Oil and Gas Reservoirs, 2nd Edition)
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