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Geosciences
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Fracture Geomechanics—Obstacles and New Perspectives
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Fracture Geomechanics—Obstacles and New Perspectives

A special issue of Geosciences (ISSN 2076-3263). This special issue belongs to the section "Geomechanics".

Deadline for manuscript submissions: 15 March 2025 | Viewed by 4425

Special Issue Editors

Dr. Wenfeng Li

E-Mail Website
Guest Editor
Earth and Environmental Sciences, Los Alamos National Laboratory, Los Alamos, NM 87545, USA
Interests: geomechanics; flow in porous media; thermo-hydro-mechanical–chemical coupling
Dr. Shahrzad Roshankhah

E-Mail Website
Guest Editor
Civil and Environmental Engineering, The University of Utah, Salt Lake City, UT, 84112, USA
Interests: renewable energy systems; thermo-hydro-mechanical–chemical coupling; porous media; acoustic emission; neutron imaging; experimental and computational geomechanics

Special Issue Information

Dear Colleagues,

The objective of this Special Issue of Geosciences is to disseminate and discuss recent advances in the geomechanics of subsurface fractures by collecting high-quality original research articles, reviews, and technical notes.

The geomechanics of fractures finds applications in many subsurface engineering disciplines at the forefront of sustainable fossil-energy extraction and green-energy transition. This is because fractures strongly impact fluid flow, solute transport, seismicity, and rock mass failure in the subsurface. Hence, there is an increasing interest in the sophisticated characterization, modeling, prediction, and management of subsurface fractures. Nevertheless, the current understanding of fracture geomechanics is fairly limited, hindering safe and efficient operations in underground mining, hydrocarbon recovery, enhanced geothermal systems, geological CO2 sequestration/mineralization, subsurface energy (H2, Gas) storage, nuclear waste disposal, etc. To push the knowledge boundary and benefit global geo-resource utilization, we would like to invite you to submit your recent work on experimental, computational modeling, and field studies of subsurface fractures with respect to the following topics:

  • Hydraulic fracturing and interactions with natural geological discontinuities;
  • Hydro-mechanical coupling of fracture and fluid flow;
  • Hydromechanical interactions of the fracture network and rock matrix;
  • Shear fracturing and seismicity;
  • Fracture geomechanics on the structural failure of underground openings (tunnels, boreholes, caves, etc.);
  • Impact of geochemical reactions on fracture geomechanics;
  • Constitutive behavior of fracture geomechanics;
  • Fracture geomechanics in the geothermal environments;
  • Monitoring of fracture geomechanical behavior;
  • Application of machine learning and probabilistic modeling in fracture geomechanics.

Dr. Wenfeng Li
Dr. Shahrzad Roshankhah
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. Geosciences 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 1800 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

  • hydraulic fracturing
  • natural fractures
  • thermo-hydro-mechanical–chemical coupling
  • process monitoring systems
  • acoustic emission
  • seismicity
  • constitutive laws
  • machine learning
  • flow in fractured porous media
  • uncertainty quantification

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Published Papers (3 papers)

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25 pages, 11268 KiB  
Article
Optimized Random Forest Models for Rock Mass Classification in Tunnel Construction
by Bo Yang, Danial Jahed Armaghani, Hadi Fattahi, Mohammad Afrazi, Mohammadreza Koopialipoor, Panagiotis G. Asteris and Manoj Khandelwal
Geosciences 2025, 15(2), 47; https://doi.org/10.3390/geosciences15020047 - 2 Feb 2025
Viewed by 229
Abstract
The accurate prediction of rock mass quality ahead of the tunnel face is crucial for optimizing tunnel construction strategies, enhancing safety, and reducing geological risks. This study developed three hybrid models using random forest (RF) optimized by moth-flame optimization (MFO), gray wolf optimizer [...] Read more.
The accurate prediction of rock mass quality ahead of the tunnel face is crucial for optimizing tunnel construction strategies, enhancing safety, and reducing geological risks. This study developed three hybrid models using random forest (RF) optimized by moth-flame optimization (MFO), gray wolf optimizer (GWO), and Bayesian optimization (BO) algorithms to classify the surrounding rock in real time during tunnel boring machine (TBM) operations. A dataset with 544 TBM tunneling samples included key parameters such as thrust force per cutter (TFC), revolutions per minute (RPM), penetration rate (PR), advance rate (AR), penetration per revolution (PRev), and field penetration index (FPI), with rock classification based on the Rock Mass Rating (RMR) method. To address the class imbalance, the Borderline Synthetic Minority Over-Sampling Technique was applied. Performance assessments revealed the MFO-RF model’s superior performance, with training and testing accuracies of 0.992 and 0.927, respectively, and key predictors identified as PR, AR, and RPM. Additional validation using 91 data sets confirmed the reliability of the MFO-RF model on unseen data, achieving an accuracy of 0.879. A graphical user interface was also developed, enabling field engineers and technicians to make instant and reliable rock classification predictions, greatly supporting safe tunnel construction and operational efficiency. These models contribute valuable tools for real-time, data-driven decision-making in tunneling projects. Full article
(This article belongs to the Special Issue Fracture Geomechanics—Obstacles and New Perspectives)
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33 pages, 6962 KiB  
Article
Experimental Study: Stress Path Coefficient in Unconsolidated Sands: Effects of Re-Pressurization and Depletion Hysteresis
by Sabyasachi Prakash, Michael Myers, George Wong, Lori Hathon and Duane Mikulencak
Geosciences 2024, 14(12), 327; https://doi.org/10.3390/geosciences14120327 - 3 Dec 2024
Viewed by 621
Abstract
Accurate estimation of in-situ stresses is a critical parameter for geo-mechanical modelling. In-situ stresses are estimated in the field from logs and frac tests. Laboratory tests are performed with cored material to estimate horizontal stress changes under defined boundary conditions to complement field [...] Read more.
Accurate estimation of in-situ stresses is a critical parameter for geo-mechanical modelling. In-situ stresses are estimated in the field from logs and frac tests. Laboratory tests are performed with cored material to estimate horizontal stress changes under defined boundary conditions to complement field data. Horizontal stress path coefficient is used to estimate a change in in-situ stresses as the reservoir undergoes depletion or injection. Uniaxial Strain boundary conditions are representative of far field stress state. The laboratory data provides the change in horizontal stress with a change in pore pressure. It is used to complement the field data acquisition of absolute stress values to predict the value of total stresses. This experimental study provides a novel method of simulating geological compaction for fabricating representative samples from unconsolidated sands. It investigates the variability of horizontal stress path coefficient as a function of changing pore pressure (depressurization and re-pressurization) in unconsolidated sandstone reservoirs. Synthetic sandstones samples were made from sand packs by consolidating them under an isostatic stress path at ambient pore pressure. After getting to initial reservoir conditions, a series of pore pressure depletion and injection tests with varying magnitudes (injection and depletion) were performed to study the effects of stress path direction and associated hysteresis. The magnitude of the stress path coefficient under depletion is lower than that under injection for the first load-unload cycle. In subsequent load-unload cycles, the stress path coefficient values remain constant until the sample is depleted to a new level of pore pressure. A Modified Cam Clay model is fit to the data to map the expansion of the yield surface and quantify the model parameters. Application of this research includes accurate prediction of changes in-situ stresses during depletion and injection stress paths for simulating unconsolidated reservoirs behavior under fluid injection or further depletion. Full article
(This article belongs to the Special Issue Fracture Geomechanics—Obstacles and New Perspectives)
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16 pages, 4074 KiB  
Technical Note
Laboratory Hydraulic Tensile Strength Correlation with Strength-Based Brittleness Indices for Carbonate Reservoirs
by Mohammad Ezazi, Ebrahim Ghorbani, Ali Shafiei, Ebrahim Sharifi Teshnizi and Brendan C. O’Kelly
Geosciences 2024, 14(2), 52; https://doi.org/10.3390/geosciences14020052 - 15 Feb 2024
Cited by 2 | Viewed by 1922
Abstract
Hydraulic fracturing (HF) is the primary choice for stimulating petroleum reservoirs. Rock tensile strength and brittleness are crucial parameters required for screening candidate reservoirs and in designing successful HF operations. However, in situ and laboratory determinations of the hydraulic tensile strength (HTS) of [...] Read more.
Hydraulic fracturing (HF) is the primary choice for stimulating petroleum reservoirs. Rock tensile strength and brittleness are crucial parameters required for screening candidate reservoirs and in designing successful HF operations. However, in situ and laboratory determinations of the hydraulic tensile strength (HTS) of rock can prove problematic. Alternatively, the HTS could be estimated from the rock brittleness once a reliable relationship has been established between them. Accordingly, this paper investigates the correlations between the HTS, as measured using laboratory hydraulic fracture tests, and ten strength-based brittleness indices (BIs) selected from the research literature. The primary inputs for computing these BIs are uniaxial compressive strength (UCS) and the Brazilian tensile strength (BTS), which are typically measured for most projects using standard laboratory rock mechanics tests or obtained from log data. For the purposes of this experimental investigation, intact rock core samples were obtained from a carbonate–dolomite formation in Iran, comprising eight distinct geomechanical units, with measured values of UCS, BTS, and HTS ranging 29.7–162.2, 1.93–12.23, and 7.20–20.63 MPa, respectively. The measured HTS was found to directly correlate with the UCS, BTS, and Young’s modulus, and inversely correlated with the rock porosity. Seven of the ten investigated BIs correlated with the measured HTS over 69% (R2 ≥ 0.69). In particular, the BI expressions developed by Yagiz and Gokceoglu, Ghadernejad et al., and Khandelwal et al. exhibited relatively strong correlations with the measured HTS (producing R2 values of 0.94, 0.87, and 0.86, respectively), suggesting that these three HTS–BI correlations could be used to provide preliminary HTS estimates for the investigated carbonate–dolomite formation in Iran. This work adds to a database that can be expanded to include other geographical regions for providing useful information about the selection of a suitable site or reserve for conducting HF operations. Full article
(This article belongs to the Special Issue Fracture Geomechanics—Obstacles and New Perspectives)
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Planned Papers

The below list represents only planned manuscripts. Some of these manuscripts have not been received by the Editorial Office yet. Papers submitted to MDPI journals are subject to peer-review.

Planned Paper 1:

Author: Vahid Tavakoli

Abstract: Reservoir heterogeneity plays an important role in the exploration, evaluation and drilling of hydrocarbon reservoirs. In the current research, the heterogeneity of a reservoir located in Permian–Triassic Kangan and Dalan formations were studied in two aspects namely petrophysical and geomechanical. Core-derived petrophysical data have been used to evaluate the petrophysical heterogeneity through rock typing process. Well-known methods of Lucia, FZI, and Winland were employed for this purpose. Geological properties of all rock types were considered using thin section studies. Laboratory measured rock strength characteristics and Schmidt Hammer rebound (SHR) data compared with the results of wire-line log analysis. These data were integrated in two-steps clustering for evaluating the geomechanical heterogeneity. Uniaxial compressive strength (UCS) was selected as the best strength characteristics of rocks for clustering and determination of geomechanical units (GMUs). Four GMUs were distinguished as the final results of clustering with good quality of clustering based on UCS and SHR. Distribution of each petrophysical rock type was considered in four GMUs using pie diagrams to demonstrate the effect of petrophysical on geomechanical heterogeneity. Results revealed that UCS and SHR have reverse relationships with porosity. Also, it was found that Lucia's method was more suitable than others to evaluate the geomechanical heterogeneity based on petrophysical changes in the reservoir. This method uses both geological and petrophysical properties and therefore can manage the geomechanical heterogeneity more effectively. Finally, according to the results, UCS parameter is more effective than SHR to determine the GMUs in studied reservoirs.

Planned Paper 2:

Title: Safety assessment of concrete gravity dams considering fracture propagation at the dam/foundation interface
Authors: Maria Luísa Braga Farinha; Nuno Monteiro Azevedo; Sérgio Oliveira
Affiliation: Laboratório Nacional de Engenharia Civil (LNEC), Lisbon, Portugal
Abstract: Given the potential of material and human losses associated to dam failure it is mandatory to adopt a framework that has the capacity to anticipate and prevent failures. The current approaches based on simplified limit equilibrium techniques are not able to characterize the complex dam/foundation behaviour, that leads to sliding along the dam/foundation interface or along rock mass discontinuities, or along rock mass layers of lower strength. The ability to assess the safety of the dam-foundation systems in an integrated way still needs to be improved, namely by incorporating coupled models that take into account the significant interdependence between the mechanical and hydraulic behaviour and by using adequate constitutive laws.
An explicit time-stepping small displacement coupled algorithm, Parmac2D-Fflow, is used to assess the safety of different gravity dams. This algorithm is based on a discrete representation of discontinuities, simulates the hydro-mechanical interaction and considers softening based constitutive laws that are closer to the actual behaviour of concrete, rock and dam/foundation interface. The adopted model allows two different approaches for the seepage flow: i) seepage occurs in all interfaces independently of their damage (the corresponding water pressures are installed from the beginning of the simulation on all interfaces); ii) seepage only occurs after joint failure, making it possible to model a coupled propagation failure along the dam/foundation interface due to a hypothetical dam overtopping scenario.
Parametric studies are carried out that evaluate the influence of both the mechanical and the hydraulic properties on the global safety factor for three different dam geometries. The numerical results predicted with a coupled/fracture propagation model are compared with those obtained with a strength reduction method. Also presented are the results obtained with a coupled model that considers seepage to occur from the beginning of the overtopping simulation. The results presented show that with the proposed coupled/fracture propagation model it is possible to identify more realistic failure modes of the dam/foundation system and, as expected, higher safety factors are obtained.

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