Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Please see PDF file.

Comments for author File: Comments.pdf

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

The topic is highly relevant and of significant current interest. Overall, the work is engaging, and the paper is well structured. The figures are clear and well prepared, too. However, to strengthen the manuscript, improve its multidisciplinary perspective and its overall impact, several aspects could be further developed:

1) The introduction does not include any reference to monitoring techniques for underground gas storage sites, either in terms of deep reservoirs or the potential surface effects they may cause;

2) The section discussing different reservoir types (p. 4) makes no reference to the typical geology of depleted fields. Furthermore, the differences between porous and fractured aquifers are not addressed, nor are the various effects that gas storage operations may have at depth and on the surface;

3) Subsection 3.4.1 does not specify which types of reservoirs are affected by the phenomenon described. Does it occur in all types of reservoirs? Does it occur in the same way in all of them? Are there any differences? Clarifying this would make the discussion more accessible, particularly for readers who are unfamiliar with the topic;

4) Chapter 4 could be improved, especially with regard to monitoring activities. Section 4.2, in particular, raises several questions: What effects could occur? What are the impacts of injection and withdrawal at depth and at the surface? Are these effects the same in porous reservoirs and salt caverns? Most importantly, are there any established methods for monitoring these effects? A substantial body of scientific literature exists on this topic. It would be useful to include references to remote sensing techniques such as InSAR and possibly dedicate a subsection to the different effects observed in different types of reservoir;

5) Subsection 4.2.1 lacks appropriate references.

6) Section 4.2.2 only focuses on fault reactivation in porous media. However, other aspects could also be discussed. For example, could the reservoir undergo seasonal expansion and contraction? Monitoring these processes is crucial in order to prevent damage and instability in storage facilities and wells used for gas storage operations;

7) In the section 'For surface safety' on page 20, there is no mention of remote sensing or InSAR techniques, despite several relevant references being present in the literature;

8) The text in Figure 7 should be enlarged to improve readability.

I believe that the authors have carried out valuable, well-organised work. Addressing the above points would further enhance the quality and impact of the manuscript.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors The authors reviewed how underground gas storage engineering systems can address sustainability challenges based on the latest global theoretical research and engineering practices. Some comments and suggestions are as follows: 1.The abstract lacked specific quantitative core conclusions, and only qualitative descriptions were made, which cannot highlight the core contributions of this review. Please include specific conclusions in Abstract, particularly highlighting quantitative findings. 2.The paper structure is missing, the authors can add a paragraph in Introduction to illustrate the main work of each section. 3.The content of Section 2.2 and Section 4.1 had a partial overlap in the description of gas physical and chemical properties; the Section 5.3 was closely related to Section 2.1, but the spatial arrangement was scattered. It is recommended to merge the repetitive content and adjust the section order to make the logical connection closer 4.The review did not clearly explain the scope definition and boundary of CO2 involved in the UGS transition. Although the authors mentioned that it is not permanent sequestration, the distinction between CO2 as cushion gas and CCUS storage is not clear enough in the manuscript. 5.For the THMCB coupling mechanism, the review only carried on the conceptual combing, but lacked the explanation of the coupling relationship and interaction mechanism between each physical field, and did not clarify the solution difficulties and current research bottlenecks of the coupling model. 6.In Section 3, the description of hydrogen embrittlement and microbial corrosion only cited existing research conclusions, and did not summarize the failure mechanism, influencing factors and prevention measures in a classified manner. 7.The Section 5.2 involved a variety of monitoring technologies, but did not clarify the applicable scenarios, technical advantages and limitations of each technology. 8.The Section 6 mentioned suggestions in synergetic storage, materials, intelligence and policies, but lacked targeted challenges and feasible technical paths corresponding to each direction.

Author Response

Please see the attachment.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have significantly improved the manuscript following the proposed revisions, adequately addressing all the comments that were raised. In my opinion, the paper is now suitable for publication.

Reviewer 3 Report

Comments and Suggestions for Authors

The authors have addressed the previous feedback and I therefore recommend accepting the manuscript for publication.