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Fractal Fract
Special Issues
Multiscale Fractal Analysis in Unconventional Reservoirs
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Multiscale Fractal Analysis in Unconventional Reservoirs

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

Deadline for manuscript submissions: 31 October 2025 | Viewed by 918

Special Issue Editor

Dr. Yang Wang

E-Mail Website
Guest Editor
School of Resources and Geoscience, China University of Mining and Technology, Xuzhou 221116, China
Interests: shale gas; coalbed methane; pore structure; adsorption mechanism; fractal characterization
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Unconventional reservoirs, such as shale gas, tight oil, and coalbed methane, have become pivotal in meeting the global energy demand. However, their inherent geological complexity and heterogeneity present significant challenges for accurate characterization, modeling, and efficient extraction. Multiscale fractal analysis offers a robust framework to quantify and interpret the intricate spatial patterns and scaling behaviors within these reservoirs. By applying fractal geometry across multiple scales, researchers can gain deeper insights into fracture networks, pore structures, and fluid flow dynamics, ultimately enhancing reservoir performance and hydrocarbon recovery.

This Special Issue, "Multiscale Fractal Analysis in Unconventional Reservoirs", seeks to compile innovative research that leverages fractal and multiscale methodologies to address the complexities of unconventional hydrocarbon reservoirs. We invite contributions that explore theoretical advancements, novel computational techniques, and practical applications of multiscale fractal analysis in various aspects of reservoir engineering. Topics of interest include, but are not limited to, the following:

  • Fractal characterization of fracture networks and pore geometries;
  • Multiscale modeling of fluid flow and transport phenomena;
  • Integration of fractal analysis with seismic interpretation and well logging;
  • Application of fractal-based methods in reservoir simulation and optimization;
  • Case studies demonstrating the practical implementation of multiscale fractal techniques;
  • Synergies between fractal analysis and other advanced technologies, such as machine learning and digital rock physics.

By bringing together diverse perspectives and cutting-edge advancements, the focus of this Special Issue is to foster interdisciplinary collaboration and drive forward the understanding and exploitation of unconventional reservoirs. We encourage researchers and industry professionals to share their latest findings, methodologies, and case studies, contributing to the advancement of sustainable and efficient energy extraction practices.

Dr. Yang Wang
Guest Editor

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

  • multiscale fractal analysis
  • unconventional reservoirs
  • fractal geometry
  • fracture network characterization
  • pore structure analysis
  • fluid flow modeling
  • reservoir simulation
  • machine learning
  • digital rock physics

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Published Papers (2 papers)

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Research

21 pages, 4797 KiB  
Article
Multifractal Characterization of Pore Heterogeneity and Water Distribution in Medium- and High-Rank Coals via Nuclear Magnetic Resonance
by Huan Liu, Shasha Zhang, Yu Qiao, Danfeng Xie and Long Chang
Fractal Fract. 2025, 9(5), 290; https://doi.org/10.3390/fractalfract9050290 - 28 Apr 2025
Viewed by 183
Abstract
Comprehensive assessment of pore structure and multiphase water distribution is critical to the flow and transport process in coalbed methane (CBM) reservoirs. In this study, nuclear magnetic resonance (NMR) and multifractal analysis were integrated to quantify the multiscale heterogeneity of nine medium- and [...] Read more.
Comprehensive assessment of pore structure and multiphase water distribution is critical to the flow and transport process in coalbed methane (CBM) reservoirs. In this study, nuclear magnetic resonance (NMR) and multifractal analysis were integrated to quantify the multiscale heterogeneity of nine medium- and high-rank coals under water-saturated and dry conditions. By applying the box-counting method to transverse relaxation time (T2) spectra, multifractal parameters were derived to characterize pore heterogeneity and residual water distribution. The influencing factors of pore heterogeneity were also discussed. The results show that pore structures in high-rank coals (HCs) exhibit a broader multifractal spectrum and stronger rightward spectrum than those of medium-rank coals, reflecting micropore-dominated heterogeneity and the complexity induced by aromatization in HCs. The vitrinite content enhances micropore development, increasing the heterogeneity and complexity of pore structure and residual water distribution. Inertinite content shows opposite trends compared to vitrinite content for the effect on pore structure and water distribution. Volatile yield reflects coal metamorphism and thermal maturity, which inversely correlates with pore heterogeneity and complexity. Residual water mainly distributes to adsorption pores and pore throats, shortening T2 relaxation (bound water effect) and reducing spectral asymmetry. The equivalence of the multifractal dimension and singularity spectrum validates their joint utility in characterizing pore structure. Minerals enhance pore connectivity but suppress complexity, while moisture and ash contents show negligible impacts. These findings provide a theoretical reference for CBM exploration, especially in optimizing fluid transportation and CBM production strategies and identifying CBM sweet spots. Full article
(This article belongs to the Special Issue Multiscale Fractal Analysis in Unconventional Reservoirs)
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20 pages, 5784 KiB  
Article
Pore Structure Evolution of Coal After Supercritical CO2–Water–Rock Treatment: A Multifractal Analysis
by Sijian Zheng, Yanzhi Liu, Fansheng Huang, Shiqi Liu, Shuxun Sang, Xuguang Dai and Meng Wang
Fractal Fract. 2025, 9(3), 144; https://doi.org/10.3390/fractalfract9030144 - 25 Feb 2025
Cited by 1 | Viewed by 370
Abstract
The evolution of coal’s pore structure is crucial to the efficient capture of carbon dioxide (CO2) within coalbeds, as it provides both adsorption sites and seepage space for the adsorbed- and free-phase CO2, respectively. However, the conventional single fractal [...] Read more.
The evolution of coal’s pore structure is crucial to the efficient capture of carbon dioxide (CO2) within coalbeds, as it provides both adsorption sites and seepage space for the adsorbed- and free-phase CO2, respectively. However, the conventional single fractal method for characterizing pore structure fails to depict the intricacies and variations in coal pores. This study innovatively applies the low-temperature N2/CO2 sorption measurement and multifractal theory to investigate the evolution of the microporous structure of coals (e.g., from the Huainan coalfield) during the supercritical CO2(ScCO2)–water–rock interaction process. Firstly, we observed that the ScCO2–water–rock interaction does not significantly alter the coal’s pore morphology. Notably, taking the ZJ-8# sample as an example, low-temperature N2 sorption testing displayed a stable pore volume following the reaction, accompanied by an increase in specific surface area. Within the CO2 sorption testing range, the ZJ-8# sample’s pore volume remained unchanged, while the specific surface and pore width performed displayed a slight decrease. Secondly, by introducing key parameters from multifractal theory (such as Dq, α(q), τ(q), and f(α)), we assessed the heterogeneity characteristics of the coal’s pore structure before and after the ScCO2–water–rock reaction. The N2 sorption analysis reveals an increase in pore heterogeneity for the ZJ-8# sample and a decrease for the GQ-13# sample within the sorption testing range. In the context of low-temperature CO2 sorption analysis, the pore distribution complexity and heterogeneity of the GQ-11# and GQ-13# samples’ pores were escalated after ScCO2–water–rock interaction. The experimental and analysis results elucidated the dual roles of precipitation and dissolution exerted by the ScCO2–water–rock interaction on the micropores of coal reservoirs, underscoring the heterogeneous nature of the reaction’s influence on pore structures. The application of fractal theory offers a novel perspective compared to traditional pore characterization methods, significantly improving the precision and comprehensiveness of pore structure change descriptions. Full article
(This article belongs to the Special Issue Multiscale Fractal Analysis in Unconventional Reservoirs)
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