Experimental Study on the Dilatancy Characteristics and Permeability Evolution of Sandstone under Different Confining Pressures
Round 1
Reviewer 1 Report
(1) Reviewers have always believed that it is necessary to appropriately present key quantitative results in the abstract of engineering papers. Because such a paper will quickly capture the reader's interest and attention.
(2) In table 1, the CO2 Pressure was designed as 2.0MPa. Is it reasonable? As we all know, when the Simulated depth is 600m, the reservoir pressure is about 6MPa. However, all injection CO2 pressure is 2MPa. The reviwer think it is not reasonale.
(3) In Figure 2a, we can see that the strain becames the nagtive calue when the Axial strain exceeds for the confining pressure of 5MPa. However, for other confining pressures, the Volumetric strain is always the positive value. Why? In Figure 3, the author depicted the fractures on the surface of the rock sample with yellow lines. It is good! However, what is the basis for distinguishing between tensile and shear fractures?
(4) The statement in lines 39-40 that "Rock permeability measures the ability of pore fluid to migrate in rock mass, and is an important indicator of oil and gas capacity." needs to be supported by some references. https://doi.org/10.1007/s11356-022-21233-7, https://doi.org/10.1007/s11356-022-19663-4, https://doi.org/10.1016/j.jpowsour.2021.230925
(5) From Figure 13, we can see that the permeability values obtained by the model do not coincide well with the experimental values at higher strain values. Please explain the reason for this.
The quality of english language needs to be moerately improved.
Author Response
(1) Reviewers have always believed that it is necessary to appropriately present key quantitative results in the abstract of engineering papers. Because such a paper will quickly capture the reader's interest and attention.
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have revised the "Abstract" in revised manuscript.
(2) In table 1, the CO2 Pressure was designed as 2.0 MPa. Is it reasonable? As we all know, when the Simulated depth is 600m, the reservoir pressure is about 6MPa. However, all injection CO2 pressure is 2 MPa. The reviewer think it is not reasonable.
Response:
Thanks for the comment. It is an objective fact that the sandstone reservoir pressure is about 6 MPa at a simulated depth of 600 m. Due to the complex effective stress behavior of different gas pressures on the seepage characteristics of sandstone, the injection pressure was uniformly set to 2 MPa. In future research, the impact of different gas pressures on the permeability and deformation behavior of sandstone will be studied.
(3) In Fig. 2a, we can see that the strain becomes the negative value when the axial strain exceeds for the confining pressure of 5 MPa. However, for other confining pressures, the volumetric strain is always the positive value. Why? In Fig. 3, the author depicted the fractures on the surface of the rock sample with yellow lines. It is good! However, what is the basis for distinguishing between tensile and shear fractures?
Response:
Thanks for the comment. In the experiment, the compressive strain is positive and the tensile strain is negative. The larger the dilatancy capacity of the sandstone specimen, the smaller or more negative the volumetric strain. An important measure of the dilatancy under different confining pressures is the change in sandstone volume. Sandstone exhibits the maximum dilatancy capacity under a confining pressure of 5 MPa, manifested by the greatest variation in volumetric strain. That is, the curve in the Fig. 2a drops even more sharply. The main criterion for distinguishing "tensile cracks" and "shear cracks" is the angle between the direction of fracture propagation and the maximum principal stress.
(4) The statement in lines 39-40 that "Rock permeability measures the ability of pore fluid to migrate in rock mass, and is an important indicator of oil and gas capacity." needs to be supported by some references. https://doi.org/10.1007/s11356-022-21233-7, https://doi.org/10.1007/s11356-022-19663-4, https://doi.org/10.1016/j.jpowsour.2021.230925
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have added relevant references to support this.
(5) From Fig. 13, we can see that the permeability values obtained by the model do not coincide well with the experimental values at higher strain values. Please explain the reason for this.
Response:
Thanks for the comment. Sandstone enters the plastic stage under higher strain, and the damage induced by microcrack propagation becomes the dominant factor for permeability recovery. In plastic region, the radial strain is closely related to crack propagation, but is not the only factor affecting permeability evolution. Therefore, it is normal for the permeability predicted by the model to deviate from the experimental value.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
This study utilizes a self-developed equipment for thermal-hydrological-mechanical coupling of rock to conduct conventional triaxial seepage tests on sandstone under different confining pressures. The results show that the gas-bearing sandstone exhibits the brittle characteristics of tensile-shear composite failure. The permeability models with volumetric strain and radial strain as independent variables were established, respectively, which could reflect the whole process of permeability evolution, and good fitting results were obtained.
The results are moderately interesting. However, I recommend the following revision:
1. The abstract is diluted. It should be compact and concise and should focus on reporting the original contributions of this paper.
2. What other methodologies can be adopted to study the dilatancy characteristics?
3. What are the limitations of the current study and the proposed methods?
4. Check the references carefully. They are not uniform and the reference nos. appear twice.
5. In the introduction, discuss the research gaps and how the current results fill them.
Minor spell check needed.
Author Response
1.The abstract is diluted. It should be compact and concise and should focus on reporting the original contributions of this paper.
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have revised the "Abstract" in revised manuscript.
2. What other methodologies can be adopted to study the dilatancy characteristics?
Response:
Thanks for the comment. By using displacement sensors, three-dimensional digital speckle, flowmeter, NMR to measure parameters such as volumetric strain, radial strain, wave velocity, permeability, porosity, etc., the dilatancy characteristics of rocks can be directly or indirectly studied.
3. What are the limitations of the current study and the proposed methods?
Response:
Thanks for the comment. The limitations of the current study do not investigate the deformation behavior of sandstone at higher confining pressures and higher gas pressures. Under higher confining pressure, sandstone is likely to be brittle-ductility transformation, and even plastic flow, resulting in uncertain porosity trend, which is of great significance for the development of gas in ultra-deep sandstone reservoirs.
4. Check the references carefully. They are not uniform and the reference nos. appear twice.
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have made corresponding corrections in the revised manuscript.
5. In the introduction, discuss the research gaps and how the current results fill them.
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have made relevant supplements and improvements to the "Introduction".
Author Response File: Author Response.pdf
Reviewer 3 Report
1) Rephrased the abstract and conclusion section.
2) Some references are also needed in Section 1. So that's why the introduction section is not enough. Must revise and add appropriate work.
3) Highlight the aim and novelty of your work.
4) Remove the typos errors throughout the paper.
5) Why authors are doing this work? What is the hurdle encountered by this study?
6) The authors should also check for any grammatical errors throughout the paper.
Extensive editing of English language required
Author Response
1. Rephrased the abstract and conclusion section.
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have re-refined the "Abstract" and "Conclusion" in the revised manuscript.
2. Some references are also needed in Section 1. So that's why the introduction section is not enough. Must revise and add appropriate work.
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have improved the "Introduction" in the revised manuscript.
3. Highlight the aim and novelty of your work.
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have made corresponding modifications in the revised manuscript.
4. Remove the typos errors throughout the paper.
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have corrected the typos errors in the revised manuscript.
5. Why authors are doing this work? What is the hurdle encountered by this study?
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have made corresponding modifications in the revised manuscript.
6. The authors should also check for any grammatical errors throughout the paper.
Response:
Thanks for the comment. According to the reviewer’s suggestion, we have corrected the grammatical errors in the revised manuscript.
Author Response File: Author Response.pdf
Round 2
Reviewer 1 Report
(1) For the comment 2 in first round, pore pressure is MPa, but the injection pressure is 2MPa. How can it be injected if the injection pressure is lower than pore pressure?
(2) For comment 3 in first round, it was explained that the tensile strain is negative. We all know that rocks can resist compressive stress, but they cannot resist tensile stress. Can rocks undergo tensile tests? This clearly does not conform to the basic logic of rock mechanics experiments, does it? In addition, the author explains that the main criterion for distinguishing between "tensile crack" and "shear crack" is the angle between the crack propagation direction and the maximum principal stress. So, what is the critical value of the included angle? What is the basis? What is the angle between each crack in the picture? Does simple annotation make the manuscript appear a bit rough and messy?
(3) For the references mentioned in Comment 4, they are all good works that can serve as supporting materials, and it is recommended to cite them.
(4) I don't think I can be convinced about the response to comment 5. What can a simple qualitative description and explanation explain?
I believe that the manuscript does not meet the requirements for acceptance and publication, and I suggest making a decision to reject it.
The language is too colloquial and requires professional institutions to polish and improve. I hinted and mentioned this in the first round of review, but the author still hasn't taken any action on it.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 2 Report
Satisfied with the revision. I recommend acceptance.
Minor spell check needed.
Author Response
Thanks for the comment.We have corrected some grammar errors in the revised manuscript.
Author Response File: Author Response.pdf
Reviewer 3 Report
I accept in current form for publication.
Author Response
Thanks for the comment.
Round 3
Reviewer 1 Report
After the improvement, the paper can be accepted for publication now.
