Discrete Element Modeling of the Effect of Hydrate Distribution Heterogeneity on the Mechanical Behavior of Cemented Hydrate-Bearing Sediments
Round 1
Reviewer 1 Report
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The models in the article are very well conceptualized.
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In the cementation hydrate morphology, a saturation of hydrates in the pores is represented as the bond strength between two adjacent sediment grains. The higher the saturation, the higher will be the bond strength, and vice versa. This needs more concrete explanation based on the fundamental physical principles.
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These simulation studies are conducted using the Discrete Element Method (DEM) modeling. The author has compared the effect of heterogeneity on the mechanical properties (shear strength, secant modulus) of the hydrate-bearing sediments (HBS). Can a commentary be added on the flow parameters linked to the changes in mechanical parameters? Suggested works: https://doi.org/10.1016/j.petrol.2020.107575, https://doi.org/10.1016/j.gr.2019.11.014, https://doi.org/10.1016/j.marpetgeo.2020.104566, https://doi.org/10.1016/j.petrol.2021.109320,
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Comments based on the Theory, Results, and Conclusions that need to be addressed.
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Numerical simulation results:
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Pg 8, eq. 7 and eq. 8, the subscripts pb_kn and pb_ten are used as abbreviations. However, they are not been described anywhere.
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Pg 11, Figure 14 (b) and Pg 12, Figure 16 (b), the color scheme of ‘pb-ten’ seems counterintuitive since the bond strength of sediment-sediment contacts induced by cemented hydrates (lines 238, 259) should increase with hydrate saturation.
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Pg 13, Figure 18 (b) is closer to the justification provided and can be used as a reference to the abovementioned comment-2.
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Discussion:
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Pg 17, Figure 24 (c), at 70% pore hydrate saturation, a significant red patch is present due to the rotation of the sediment grains. However, it is not the case with the other five figures (24(a), (b), (d), (e), and (f)). Any specific reason? (Justification - pg 15, lines 350-353)
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Pg 18, Figure 25 (c), the plot for the SH40-PH-45 line does not follow the trend mentioned (lines 379-380) ‘The broken bond number increases with decreasing pore hydrate saturation’. Justification is required.
The conclusions drawn are well-matched with the simulation results and discussion.
Author Response
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Author Response File: 
Author Response.pdf
Reviewer 2 Report
Line 40 in the Introduction: "Only several field trial tests...": make some examples and briefly discuss them, particularly highlighting the aspects which are not been still adequately addresses. The following article could be useful: CO2 hydrate properties and applications: A state of the art. Progress in Energy and Combustion Science, 93 (2022) 101026.
Line 49 - 54: this description is too general and must be extendend. The following article could be useful: Thermodynamic and kinetic characterization of methane hydrate ‘nucleation, growth and dissociation processes, according to the labile Cluster theory. Chemical Engineering Journal, 425 (2021) 130706.
In the text, the dependency of the presented results from the properties of the sediment, chosen for the analyses, is not completely clear. I think this concept is highly important for this article. More details, about the typlogy of sand selected, should be inserted in the text. Moreover, a brief sensitivity analisys regarding the effected obtained by repeating the evaluations with different sands, would be of interest for lecturers.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Review of
DEM modeling of the effect of hydrate distribution heterogeneity on the mechanical behavior of cemented hydrate-bearing sediments
This study utilises DEM for the investigation of the geomechanical characteristics of hydrate-bearing sediments by accounting for the effect of the hydrate saturation on the mechanical behaviour of simulated hydrate bearing sediment models. The manuscript reads well and can be accepted for publication after the following comments are addressed by the authors:
- The introduction is interesting but needs to be completed. The authors point out the importance of the naturally occurring gas hydrates from the energy perspective. However, natural gas hydrates and their interaction with the host sediment are very important from the environmental viewpoint. The authors are required to add these details to the manuscript. They may refer to the following articles for more information:
· Hassanpouryouzband, Aliakbar, et al. "Gas hydrates in sustainable chemistry." Chemical society reviews 49.15 (2020): 5225-5309.
· Farahani et al., 2021. Insights into the climate-driven evolution of gas hydrate-bearing permafrost sediments: Implications for prediction of environmental impacts and security of energy in cold regions. RSC advances, 11(24), pp.14334-14346.
· Farahani et al., 2021. Development of a coupled geophysical–geothermal scheme for quantification of hydrates in gas hydrate-bearing permafrost sediments. Physical Chemistry Chemical Physics, 23(42), pp.24249-24264.
· Ruppel and Kessler, 2017. The interaction of climate change and methane hydrates. Reviews of Geophysics, 55(1), pp.126-168.
- Please add more details to the caption of Figure 1.
- Please add a brief discussion on the effect of the former gas on the hydrate formation and pore-scale distribution in relation with the contents in Figure 2.
- The authors can add a brief discussion on the other numerical methods used for simulation of the mechanical behaviour of hydrate bearing sediments and the advantages of DEM over these methods with a particular interest in their ability to model pore-scale habit of hydrates. This can help the reader better understand the importance of using DEM.
- In Model Setup, please add more details to clarify where the values of the input parameters for the grains come from. Please also discuss what “Experiment” means in Figure 3 and clarify why there are deviations in the size distribution of the grains in DEM model from the experimental data.
- Please add a brief discussion on how considering the grains as discs and the problem in 2D can result in the deviation of the results from real condition because natural grains are three dimensional and irregular.
- The authors used PFC2d to make their model. They need to add more details about how the model is built in the software. A flow chart can also be used to show how their DEM model works.
- In Figure 9 and Eq.(2)-(6), please ensure that the parameters are defined.
- In Figure 11, what “pb_ten” means? Please also ensure that the parameters of the colour bars have their unit!
- Exponential equations have been fitted to the bond normal stiffness and strength values versus hydrate thickness to the grain radius. Please discuss whether an exponential behaviour would be expected?
- The discussion of the results on the effect of macroscopic heterogeneity on the mechanical behaviour of hydrate bearing sediments is inadequate, and the authors did not discuss the effect of different distribution patterns on the mechanical behaviours observed in Figures 15 and 17. Please add more details.
- Please comment on how Equation 11 can be considered as the hydrate heterogeneity index. Is it derived by the authors? If not please add the relevant reference.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 4 Report
The paper proposes a pore-scale method to model cemented hydrate-bearing sediments (HBSs) and capture the hydrate distribution heterogeneity. Through biaxial compression tests with flexible boundaries, the mechanical behavior of HBSs with different macroscopic and microscopic hydrate distribution heterogeneity is investigated. The study reveals that the mechanical properties of HBSs are influenced by both macroscopic and microscopic hydrate distribution heterogeneity, and the deformation behavior and bond breakage evolution of HBSs depend on hydrate distribution heterogeneity.
The manuscript under consideration exhibits both practical and theoretical relevance for future studies. However, before it can be accepted for publication, the suggested corrections must be incorporated.
I recommend do not use “DEM” in the title but “The discrete element method”
Also, I recommend changing the title as follows: The discrete element method modeling of the effect of hydrate distribution heterogeneity. The second part of the title will be reflected in the abstract and the main text.
The Introduction section of the paper requires a more thorough literature review to provide greater context and clarity regarding the importance of the study. It would be beneficial for the authors to include a clear and concise explanation of the study's significance and its relevance to the broader field of research.
Please analyze mentioned below papers in the field of gas hydrate development study. You are asked to consider them in your paper.
Klymenko, V.; Ovetskyi, S.; Martynenko, V.; Vytiaz, O.; Uhrynovskyi, A. An alternative method of methane production from deposits of subaquatic gas hydrates. Min. Miner. Depos. 2022, 16(3), 11-17. https://doi.org/10.33271/mining16.03.011
Bazaluk, O.; Sai, K.; Lozynskyi, V.; Petlovanyi, M.; Saik, P. Research into Dissociation Zones of Gas Hydrate Deposits with a Heterogeneous Structure in the Black Sea. Energies, 2021, 14(5), 1345. https://doi.org/10.3390/en14051345
Are the anticipated outcomes of this study applicable or transferable to other gas hydrate placement scenarios? If so, what are the potential implementation strategies and associated limitations?
Try to explain in the methods:
- What is the proposed pore-scale method for modeling cemented hydrate-bearing sediments (HBSs)?
- How is the effect of macroscopic and microscopic hydrate distribution heterogeneity on the mechanical behavior of HBSs investigated in this study?
- What types of macroscopic and microscopic hydrate distribution heterogeneity are considered in the series of DEM simulations performed in this study?
- What is the significance of the use of the Discrete Element Method (DEM) in this study's investigation of the mechanical behavior of HBSs?
Lines 375-377 “The evolutions of bond breakage in longitudinally heterogeneous DEM specimens are similar even though the distributions of hydrate layers are different”. Why? Please explain this sentence in more details.
Kindly offer a brief explanation of future research. It helps to clarify the direction and focus of future research to the readers and other researchers in the field as well as It helps to demonstrate the relevance and importance of the current research in the broader field of study.
The novelty of the paper must be highlighted in the conclusions section.
Overall, I would like to acknowledge the authors for conducting a very impressive study, and I am inclined to recommend their paper for publication provided that all the points are thoroughly reviewed and revised.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
The article has been improved in quality and can be now processed for publication in JMSE.
Author Response
We greatly appreciate your comments and suggestions that helped improve the manuscript.
Reviewer 4 Report
Dear authors, I am almost satisfied with the corrections provided by the authors after the revision. At the same time, I would like to pay your attention once more to the paper https://doi.org/10.33271/mining16.03.011. In this study a new method has been created to determine the distance at which the emissions from a mud volcano can generate enough heat to dissociate methane hydrates from the seafloor, resulting in the release of methane gas. This algorithm is crucial because it can help scientists and engineers better understand the potential hazards of mud volcanoes and methane hydrates in the ocean. By accurately predicting the distance at which methane hydrates can be dissociated, researchers can develop strategies to mitigate the release of methane into the atmosphere, which is a potent greenhouse gas. Additionally, understanding how mud volcanoes behave and the impact of their emissions on the environment can help in improving safety measures for offshore drilling operations. This study is worth your attention.
Author Response
Thank you for your suggestion. The suggested paper has been cited in the manuscript. The details can be found on lines 52-53 in the revised manuscript.
