PONE-D-24-35292Mechanical Properties Research of Unconsolidated Hydrate-Bearing Sediments under the Effect of Clay MineralsPLOS ONE

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 This work had been financially supported by the Dongying Science Development Fund (DJ2023001), the National Natural Science Foundation Project of China (51974353, 51991362, 52104014), the Natural Science Foundation of Shandong Province (ZR2019ZD14), the CNPC Major Science and Technology Project (ZD2019−184−003) and the Project Establishment and Construction Team of Young and Innovative Talents Introduction and Education Plan of Colleges and Universities in Shandong Province. 

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in Shandong Province.

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Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #1: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: No

Reviewer #2: Yes

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3. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #1: Yes

Reviewer #2: Yes

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Reviewer #1: Yes

Reviewer #2: Yes

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5. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #1: The authors tried to explore the effect of clay minerals on mechanical properties of hydrate-bearing silt-clay mixture according to many triaxial shearing tests. However, determination of the hydrate saturation has not been clearly introduced, and I guess the authors calculate the hydrate saturation by assuming all the pore water could be formed as methane hydrate. If so, there will be obvious errors especially when the specimen is consisted of fine sands and clays. As we all know that clay minerals have a strong capability to absorb water at its surface, and these water molecules are constrained by electric force. Under this condition, quite a lot of pore water could not react with methane gas to form methane hydrate. This could also explain what has been shown in the figures. For example, Figure 12, when the clay content is high, indicating intensive clay absorbed water in pores, methane hydrate saturation is low when subjected to the same mixed water in soils. This could also weaken he elastic modulus. The third conclusion “when the content ratio of montmorillonite/illite decrease, the peak strength and elastic modulus increase”. This could be also a result of that montmorillonite has a stronger capability to absorb water molecules than illite. The authors should carefully check with this point.

The authors summarized the basic knowledge related to the manuscript topic and found a gap that “researches … fail to consider NGH decomposition, clay content and clay type.” However, related effort has been reported, and here just name a few published papers that the authors may consult. Jiang et al., (2024), Advances in Geo-Energy Research, 11(1): 41-53; Li et al., (2021), Advances in Geo-Energy Research, 5(1): 75-86; Zhang et al., (2024), Measurement, 238, 115369.

Equation (1): The left-hand side is a pressure dimension. However, the dimension of the right-hand side is unknown.

Figure 3: For clays, plastic and liquid limits are much more important than the grain size distribution. Thus, testing data of the limits should be added, and the overall grain size distribution of clay-silt mixtures will be better than the separated grain size distribution.

Reviewer #2: The present paper intends to explore the mechanical properties of unconsolidated hydrate sediments, analyze variation laws and underlying reasons by considering hydrate saturation, effective confining pressure, clay content and clay type. This is helpful for wellbore instability analysis and sand production prediction, which is very interesting and meaningful. However, there are still few questions need to be clarified and discussed.

1. Common clay types include kaolinite, montmorillonite, illite and chlorite. This paper mainly discusses montmorillonite and illite, which are believed the main composition of shallow clay minerals in Shenhu sea area. What about kaolinite and chlorite? The type, content and distribution characteristics of clay minerals in Shenhu sea area should be supplemented detailedly in the introduction.

2. Some details of the experiment need to be discussed. Are the gas hydrate samples prepared and tested in one cell or in different? What is the initial water saturation? What methods are used to prepare uniform samples?

3. In the paper, there is no information on the place where the temperature is measured. In addition, temperature has a significant impact on the mechanical properties of hydrate sediment. The higher the clay content, the more obvious the effect may be. What is the temperature variation during the mechanical testing? Would this variation have an impact on test results and model establishment? The effect of temperature on unconsolidated hydrate sediments is not considered in this paper, and can be the future research direction (I share a good idea and conception with the Authors).

4. In the experiment, how to get the desired hydrate saturation by hydrate depressurization decomposition? Does the hydrate samples remain uniform during the process?

5. This paper gives the influence of two clay minerals, montmorillonite and illite, on the mechanical properties and strength parameters, which clay mineral has greater influence? Why?

6. The latest references are listed in the paper. However, there are few format issues in the reference. Carefully proofread the reference and unify the author's name citation format.

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Reviewer #1: No

Reviewer #2: No

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Mechanical Properties Research of Unconsolidated Hydrate-Bearing Sediments under the Effect of Clay Minerals

PONE-D-24-35292R1

Dear Dr. Sun,

We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements.

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Kind regards,

Jianguo Wang, PhD

Academic Editor

PLOS ONE

Additional Editor Comments (optional):

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: (No Response)

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2. Is the manuscript technically sound, and do the data support the conclusions?

The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented.

Reviewer #2: (No Response)

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: (No Response)

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4. Have the authors made all data underlying the findings in their manuscript fully available?

The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified.

Reviewer #2: (No Response)

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5. Is the manuscript presented in an intelligible fashion and written in standard English?

PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here.

Reviewer #2: (No Response)

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6. Review Comments to the Author

Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters)

Reviewer #2: (No Response)

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Reviewer #2: No

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