Evaluation of Caprock Sealing Performance for CO₂ Saline Aquifer Storage: A Numerical Study

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The paper presents a relevant topic, which may attract the readership of this journal. I endorse this publication with the following minor comments for further improvement:

1- The literature review is shallow with no publications cited from 2023 and 2024 and out of mere 9, there are 2 from 2022.

2- Not clear how properties and values were selected for numerical simulation. The authors may wish to add a table of critical parameters used for modelling.

3- Table 1: any references for the used criteria? Or these are proposed by the authors (in latter case, this will warrant more information).

4- Figures 3, 4, 5 and 6 have poor graphics and the embedded text is not readable. Please re-draw and use a better scale/ font size.

5- Graphics of some of the figures and equations are inconsistent and warrant improvements.

6- English quality needs significant improvement, especially from a native speaker or a professional editing service.

7- Conclusions are too general. You may wish to quantify the results with values and present them in bullets or numbers.

8- Add scope and limitations of your work and also add its possible practical implications.

9- Add references with equations adopted from others.

10- Avoid abbreviations and short forms in the abstract.

Comments on the Quality of English Language

Quality of English needs some improvement.

Author Response

1- The literature review is shallow with no publications cited from 2023 and 2024 and out of mere 9, there are 2 from 2022.

Response: Thanks for your valuable advice. We have expanded the literature review in the Introduction, including recent studies and analyzing the current technological landscape. We have also clarified the paper's objectives and the innovation of our technical approach.

The updates can be found in lines 31-42 and lines 68-78 of the revised manuscript.

2- Not clear how properties and values were selected for numerical simulation. The authors may wish to add a table of critical parameters used for modelling.

Response: Thanks for your guidance. Thank you for your guidance. We have included a table of critical geological parameters in Section 2, "Geological Setting," detailing reservoir characteristics.

The updates can be found in lines 86 - 96 of the revised manuscript.

3- Table 1: any references for the used criteria? Or these are proposed by the authors (in latter case, this will warrant more information).

Response: Thanks for your valuable advice. We have now cited the sources for the criteria in Table 5.

The added content can be found in Table 5, line 180 of the revised manuscript.

4- Figures 3, 4, 5 and 6 have poor graphics and the embedded text is not readable. Please re-draw and use a better scale/ font size.

Response: Thanks for your valuable advice. We have redrawn these figures to improve clarity and readability.

5- Graphics of some of the figures and equations are inconsistent and warrant improvements.

Response: Thank you for pointing this out. We have made modifications to the figures and formulas in the paper, updated the images, and standardized the notation of formula symbols.

6- English quality needs significant improvement, especially from a native speaker or a professional editing service.

Response: Thank you for your suggestions. We have rechecked and revised the content of the main text, corrected sentence descriptions, grammar and textual errors, and streamlined the description of large paragraphs. We also engaged the recommended language service to polish the texts. We hope that this revision can improve the language proficiency of our paper and make it easier for readers to understand.

7- Conclusions are too general. You may wish to quantify the results with values and present them in bullets or numbers.

Response: Thank you for your suggestions on modification. According to your suggestion, we have revised the conclusion content, clarified the innovation points, and briefly described the quantitative research results.

8- Add scope and limitations of your work and also add its possible practical implications.

Response: Thank you for your suggestions on modification. We have added Tables 1-4 to present the inputs into the simulation model, which are the data derived from a single well. It is true that these data may not fully represent the reservoir parameters, which can cause inaccuracy of the results. We have demonstrated such limitation of the work in lines 86-92.

9- Add references with equations adopted from others.

Response: Thank you for your suggestions on modification. We have added new references and revised the format and content of all the literature.

10- Avoid abbreviations and short forms in the abstract.

Response: Thank you for your suggestions on modification. We have defined all abbreviations, including those in the abstract.

Reviewer 2 Report

Comments and Suggestions for Authors

This study is critical for ensuring the safety and sustainability of caprock seal integrity in CO2 saline aquifer storage. The research identifies three primary mechanisms for top caprock failure: gradual CO2 leakage through the overlying layer, capillary seal failure due to pressure increase from CO2 injection, and caprock rupture caused by local overpressure. By combining numerical simulations and geomechanics, this study proposes a comprehensive seal assessment for caprock. The paper is purely a numerical study, so it needs further discussion on the differences with actual cases. The detailed revisions should be done as:

1.     The study title should emphasize that this is a numerical study. It is recommended to change the paper's title to: "Evaluation of Caprock Sealing Performance for CO2 Saline Aquifer Storage: A Numerical Study."

2.     The author’s affiliation should be changed to 1, 2. On Page 1, lines 5-8, the numerical superscript for affiliations is inconsistent in size, and for affiliation 3, it is better to provide the full name for CNOOC.

3.     In heading 3.1, the abbreviation THMC needs to be defined earlier.

4.     On page 1, line 33, the period before [4-7] needs to be removed.

5.     On page 4, line 121, remove the semicolon after “4.”

6.     Since the paper is purely a numerical simulation study, the authors need to discuss how to ensure consistency between real-world scenarios and the simulation results. This requires a dedicated discussion.

 

7.     Discuss what gaps exist between actual problems and the model study in this paper, and address these specifically.

Comments on the Quality of English Language

Extensive editing of English language required

Author Response

• The study title should emphasize that this is a numerical study. It is recommended to change the paper's title to: "Evaluation of Caprock Sealing Performance for CO₂Saline Aquifer Storage: A Numerical Study."

Response: Thank you for advice. The title has been revised

• The author’s affiliation should be changed to 1, 2. On Page 1, lines 5-8, the numerical superscript for affiliations is inconsistent in size, and for affiliation 3, it is better to provide the full name for CNOOC.

Response: Thank you for pointing it out. The numerical superscripts have been standardized. The designation of 'Affiliation 3' has been changed to its official name.

• In heading 3.1, the abbreviation THMC needs to be defined earlier.

Response: Thank you for pointing it out. We have made the changes as suggested.

• On page 1, line 33, the period before [4-7] needs to be removed.

Response: Thank you for pointing it out. We have made the changes as suggested.

• On page 4, line 121, remove the semicolon after “4.”

Response: Thank you for pointing it out. We have made the changes as suggested.

• Since the paper is purely a numerical simulation study, the authors need to discuss how to ensure consistency between real-world scenarios and the simulation results. This requires a dedicated discussion.

Response: We thank the reviewer for the advice. According to reviewer 1’s suggestion, we have added Tables 1-4 to present the inputs into the simulation model, which are the data derived from a single well. In practical use, data from multiple wells are recommend to improve the accuracy of the results. The corresponding content can be found on line 86 - 92.

• Discuss what gaps exist between actual problems and the model study in this paper, and address these specifically.

Response: We thank the reviewer for pointing it out. Previous studies lack integration of both physical properties and CO₂-water-rock reactions in estimating caprock sealing performance. This study filled the gap by proposing a simulation work considering thermal-fluid-solid-chemical processes , which to our knowledge, has never been performed. We have added the statements of this innovation in the conclusion section (lines 254-261).

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The revision is good. This manuscript can be accepted for publishing.