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Fracture Mechanics and Energy Geo-Structures
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Fracture Mechanics and Energy Geo-Structures

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "H: Geo-Energy".

Deadline for manuscript submissions: closed (20 December 2022) | Viewed by 6653

Special Issue Editor

Prof. Dr. Yu Wang

E-Mail Website
Guest Editor
Department of Civil Engineering, School of Civil and Resource Engineering, University of Science and Technology Beijing, Beijing 100083, China
Interests: rock mass geomechanics; hydraulic fracturing; fatigue and fracture; fracture mechanics; oil and gas development
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Unconventional oil and gas reservoirs are commonly characterized by complex geological structures such as rich bedding and natural fractures, strong inhomogeneity and anisotropy. These characteristics lead to significant challenges for drilling and production, such as wellbore instability, stuck pipe, limited stimulated rock volume, low hydraulic fracture conductivity, and rapid decline of production rate. Tackling these challenges calls for further research in geomechanical theories, methodologies, experiments, and engineering practices. The fracture mechanic is an efficient tool to help to understand rock deformation and failure mechanisms, in-situ stress prediction, wellbore stability evaluation, well trajectory design and hydraulic fracturing optimization.

This Special Issue aims to present and disseminate the most recent advances related to the theory, experiments, modelling, and application of fracture mechanics to unconventional oil and gas development.

Topics of interest for publication include, but are not limited to:

  • Multiscale geo-structures identification.
  • Multiscale rock fracture behaviors.
  • Optimization of hydraulic fracturing design in oil/gas/geothermal reservoirs.
  • New apparatus and methods for to observe and capture micro-cracks.
  • Novel laboratory testing approaches or in-situ experiments.
  • New theory to describe the fracture progress under coupled thermal–hydrological–mechanical–chemical conditions.
  • Constitutive equation and parameter identification involved in fracture models.
  • Machine learning and data-driven techniques in rock damage and fracture.
  • Fatigue-induced rock fracture predication and expression.

Dr. Yu Wang
Guest Editor

Manuscript Submission Information

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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. Energies is an international peer-reviewed open access semimonthly 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 2600 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

  • rock fracture
  • geo-structure identification
  • hydraulic fracturing
  • multiscale fracture
  • oil and gas
  • natural fracture
  • fracture conductivity

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Published Papers (4 papers)

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Research

17 pages, 40670 KiB  
Article
Insight into the Effect of Natural Fracture Density in a Shale Reservoir on Hydraulic Fracture Propagation: Physical Model Testing
by Jihuan Wu, Xuguang Li and Yu Wang
Energies 2023, 16(2), 612; https://doi.org/10.3390/en16020612 - 4 Jan 2023
Cited by 1 | Viewed by 1678
Abstract
Here, laboratory tests were conducted to examine the effects of natural fracture density (NFD) on the propagation of hydraulic fracture (HF), HF and natural fracture (NF) interaction, and the formation of the stimulated reservoir volume (SRV). Laboratory methods were proposed to prepare samples [...] Read more.
Here, laboratory tests were conducted to examine the effects of natural fracture density (NFD) on the propagation of hydraulic fracture (HF), HF and natural fracture (NF) interaction, and the formation of the stimulated reservoir volume (SRV). Laboratory methods were proposed to prepare samples with dense, medium and spare discrete orthogonal fracture networks. After conducting a true triaxial hydraulic fracturing experiment on the synthetic blocks, the experimental results were analyzed by qualitative failure morphology descriptions, and the quantitative analysis used two proposed new indices. On the pump pressure profiles, it reflected the non-linear interactions between HFs and NFs well. For rock blocks with a dense DFN density, pump pressure curves present fluctuation shape and the degree of interaction between HF and NF is strong; however, for model blocks with a sparse DFN density, the pump pressure curves present a sudden drop shape. In addition, different propagation behaviors of NFs—offset, divert, branch, and cross NF—can be observed from the fractured model blocks. By using a proposed index of “P-SRV”, the relationship between NFD and the fracturing effectiveness was further confirmed. Furthermore, the most striking finding is that mixed mode I–II and I–III fracture types can be formed in the naturally fractured model blocks. The experimental results are beneficial for grasping the influential mechanism of NFD on the propagation of HF and for developing more accurate and full 3D-coupled simulation models for unconventional oil and gas development. Full article
(This article belongs to the Special Issue Fracture Mechanics and Energy Geo-Structures)
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17 pages, 6982 KiB  
Article
Dynamic Response Characteristics of Roadway Surrounding Rock and the Support System and Rock Burst Prevention Technology for Coal Mines
by Dong Xu, Mingshi Gao and Xin Yu
Energies 2022, 15(22), 8662; https://doi.org/10.3390/en15228662 - 18 Nov 2022
Cited by 11 | Viewed by 1424
Abstract
Anchor cables (bolts) act as the main support system and play an important role in improving the rock burst resistance and stability of the roadway surrounding the rock. In this study, the dynamic response characteristics of the roadway surrounding the rock and the [...] Read more.
Anchor cables (bolts) act as the main support system and play an important role in improving the rock burst resistance and stability of the roadway surrounding the rock. In this study, the dynamic response characteristics of the roadway surrounding the rock and the support system under different shock intensities were investigated. The following findings were obtained. The stress wave propagation process under dynamic shock was divided into a stress vibration initiation stage, a stress fluctuation stage, and a stress adjustment stage. In the stress vibration initiation stage, the surface mass of the roadway surrounding the rock started to vibrate, and the pretension of the anchor cables (bolts) was reduced; in the stress fluctuation stage, the failure of the roadway surrounding the rock intensified, and the anchor cables (bolts) were damaged to some extent; and in the stress adjustment stage, the roadway deformation of the surrounding rock and the axial forces of the anchor cables (bolts) tended to stabilize. As the dynamic shock intensity increased, the vibration velocity, displacement increment, and acceleration amplitude of the mass of the roadway surrounding the rock increased exponentially. The critical shock energy of the roadway surrounding the rock was 105 J, above which the damage to the rock was aggravated. The larger the pretension of the anchor cables (bolts) was and the higher the dynamic shock intensity was, the more severe the damage to the anchor cables (bolts) was. Given the dynamic response characteristics of the roadway surrounding the rock and support elements under shock, a full anchor cable yielding support technology is proposed to effectively control the stability of the roadway surrounding the rock under dynamic shock, providing a reference for the construction of the support systems for preventing rock bursts in similar roadways. Full article
(This article belongs to the Special Issue Fracture Mechanics and Energy Geo-Structures)
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19 pages, 12506 KiB  
Article
Characteristics of the Fracture Process Zone for Reservoir Rock with Various Heterogeneity
by Hongran Chen, Jingrui Niu and Mengyang Zhai
Energies 2022, 15(22), 8332; https://doi.org/10.3390/en15228332 - 8 Nov 2022
Cited by 4 | Viewed by 1664
Abstract
Hydraulic fracturing for oil-gas and geothermal reservoir stimulation is closely related to the propagation of Mode I crack. Nonlinear deformation due to rock heterogeneity occurs at such crack tips, which causes the fracture process zone (FPZ) to form before the crack propagates unsteadily. [...] Read more.
Hydraulic fracturing for oil-gas and geothermal reservoir stimulation is closely related to the propagation of Mode I crack. Nonlinear deformation due to rock heterogeneity occurs at such crack tips, which causes the fracture process zone (FPZ) to form before the crack propagates unsteadily. However, the relationship between the FPZ characteristics and rock heterogeneity still remains elusive. We used three rock types common in reservoirs for experimental investigation, and each of them includes two subtypes with different heterogeneity due to grain size or microstructural characteristics. Drawing on the experiment results, we calculated the FPZ size (represented by the radius of an assumed circular FPZ) in each cracked chevron-notched Brazilian disk, and we reproduced the formation process of the FPZ in marble using the discrete element method. We showed that strong heterogeneity is favorable to large FPZ size, can enhance the ability of crack generation and make crack morphology complex. Coupling the Weibull distribution with fracture mechanics, the dependence of the FPZ size on heterogeneity degree can be theoretically explained, which suggests that the inherent heterogeneity of rocks sets the physical foundation for formation of FPZs. These findings can improve our recognition of propagation mechanisms of Mode I cracking and provide useful guidelines for evaluating reservoir fracability. Full article
(This article belongs to the Special Issue Fracture Mechanics and Energy Geo-Structures)
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Graphical abstract

25 pages, 7165 KiB  
Article
Experimental Study on the Effect of Bedding on the Fracture Process Zone of Shale
by Tiewu Tang, Xiaoshan Shi, Xiaojing Zhu and Liyun Li
Energies 2022, 15(17), 6359; https://doi.org/10.3390/en15176359 - 31 Aug 2022
Cited by 3 | Viewed by 1375
Abstract
The conventional fracture in shale hydraulic fracturing belongs to the type-I fracture, and the size of the fracture process zone (FPZ) is an important index to measure the fracability of rock mass. This index is also one of the feasible entry points to [...] Read more.
The conventional fracture in shale hydraulic fracturing belongs to the type-I fracture, and the size of the fracture process zone (FPZ) is an important index to measure the fracability of rock mass. This index is also one of the feasible entry points to study the complexity of the fracture network. In order to visually observe the type-I FPZ at the tip of shale fractures, and to study the relationship between the mechanical properties, the shape and size of the FPZ, and the bedding structure, Notched Semi-Circular Bend (NSCB) tests were conducted with three typical fracture direction-bedding orientations (splitter, arrester, divider). The digital image correlation (DIC) method was used to realize the intuitive observation of the real fracture process and the FPZ near the fracture tip. The test found that the FPZ of shale is narrow and long as a whole and is “flame-like”. The height-to-length ratio of the FPZ at the fracture tip determines whether bending and deflection happen between the new fracture and the prefabricated cracks when the fracture occurs. Most of the specimens often appear in the FPZ with a beaded high shear strain zone before the fracture, which is caused by the oblique communication of micro-cracks in the FPZ before the fracture. The appearance of a beaded zone of high shear strain indicates that macroscopic fracture is imminent. The research results can be used for the design of disaster early warning and prevention programs. Full article
(This article belongs to the Special Issue Fracture Mechanics and Energy Geo-Structures)
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