Gridding Effects on CO₂ Trapping in Deep Saline Aquifers

Round 1

Reviewer 1 Report

The concept of the paper is very good.

The write-up is also ok.

The authors must show their main contribution in the introduction section of the manuscript.

Try to elaborate the result section by introducing more discussion on results.

Author Response

We would like to express our sincere gratitude to the reviewers for their thorough revision of the paper and valuable suggestions to improve it.

We have addressed all the points raised by the reviewers. In the following, we provide the details of the modifications we have implemented in the revised manuscript.

We hope that now the paper can qualify for publication.

Thank you all for your time.

Best,

Alessandro, Costanzo, Christoforos, and Francesca

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• The concept of the paper is very good.
• The write-up is also ok.

We thank the reviewer for his/her appreciation of the paper.

• The authors must show their main contribution in the introduction section of the manuscript.

We added two sentences at the very end of the introduction to clarify our contribution.

• Try to elaborate the result section by introducing more discussion on results.

We have expanded the discussion of results and introduced comments on the obtained results in the “Discussion and conclusion” section.

Reviewer 2 Report

The following major revisions are proposed:

-        All data related to pressures should be in units of the international system, MPa instead of bar.

-        It would not be bad to include some more reference to the latter or to the last two years.

-        The model design should be explained in more detail, also clarifying the research assumptions. The methodology section should be more comprehensive in order to be publishable.

-        The conclusions should be a bit more detailed to make the robustness and applicability of the model clearer and how the discretization influences the downhole pressure and CO2 storage simulation should be explained in more detail.

Author Response

We would like to express our sincere gratitude to the reviewers for their thorough revision of the paper and valuable suggestions to improve it.

We have addressed all the points raised by the reviewers. In the following, we provide the details of the modifications we have implemented in the revised manuscript.

We hope that now the paper can qualify for publication.

Thank you all for your time.

Best,

Alessandro, Costanzo, Christoforos, and Francesca

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• All data related to pressures should be in units of the international system, MPa instead of bar.

We changed all pressure units (including tables and plots) from bar to MPa as recommended by the reviewer.

• It would not be bad to include some more reference to the latter or to the last two years.

We have added the following recent references to the ones in the original manuscript (we have also eliminated some less relevant references that we had originally listed):

• Abou-Kassem, Rafiqul Islam, Farouq-Ali. Petroleum Reservoir Simulation - The Engineering Approach. 2019. Gulf Professional Publishing, Elsevier, pp. 526. ISBN: 9780128191507.
• Singh, M.; Chaudhuri, A.; Soltanian, M.R.; Stauffer, P.H. Coupled Multiphase Flow and Transport Simulation to Model CO2 Dissolution and Local Capillary Trapping in Permeability and Capillary Heterogeneous Reservoir. International Journal of Greenhouse Gas Control 2021, 108, 103329.
• Al-Khdheeawi, E.A.; Mahdi, D.S.M.; Ali, M.; Iglauer, S.; Barifcani, A. Reservoir Scale Porosity-Permeability Evolution in Sandstone Due to CO2 Geological Storage. SSRN Journal 2021.
• Md Yusof, M.A.; Mohamed, M.A.; Md Akhir, N.A.; Ibrahim, M.A.; Saaid, I.M.; Idris, A.K.; Idress, M.; Awangku Matali, A.A.A. Influence of Brine–Rock Parameters on Rock Physical Changes During CO2 Sequestration in Saline Aquifer. Arab J Sci Eng 2022, 47, 11345–11359.
• Vo Thanh, H.; Lee, K.-K. Application of Machine Learning to Predict CO2 Trapping Performance in Deep Saline Aquifers. Energy 2022, 239, 122457.
• Punnam, P.R.; Krishnamurthy, B.; Surasani, V.K. Investigations of Structural and Residual Trapping Phenomena during CO2 Sequestration in Deccan Volcanic Province of the Saurashtra Region, Gujarat. International Journal of Chemical Engineering 2021, 2021, 1–16.
• Gholami, R.; Raza, A.; Iglauer, S. Leakage Risk Assessment of a CO2 Storage Site: A Review. Earth-Science Reviews 2021, 223, 103849.
• Erfani, H., Babaei, M., & Niasar, V. Dynamics of CO2 density-driven flow in carbonate aquifers: Effects of dispersion and geochemistry. Water Resources Research 2021, 57, e2020WR027829.
• Bakhshian, S. Dynamics of Dissolution Trapping in Geological Carbon Storage. International Journal of Greenhouse Gas Control 2021, 112, 103520.

We would like to specify that the technical content of the paper has not changed based on these new references. Actually, they confirmed that all the relevant concepts had already been captured and commented.

• The model design should be explained in more detail, also clarifying the research assumptions.

More details and explanations have been added to the Model description section to clarify the reasons for the model parameters and assumptions.

• The methodology section should be more comprehensive in order to be publishable.

The methodology section was expanded both by moving here the discussion on trapping mechanisms (this part was originally in the Introduction) and by adding an explanation of why attention was focused on solubility and trapping mechanisms.

This modification also addressed the comment from another reviewer, who recommended shortening the Introduction by moving the discussion on trapping mechanisms elsewhere in the paper.

• The conclusions should be a bit more detailed to make the robustness and applicability of the model clearer and how the discretization influences the downhole pressure and CO2 storage simulation should be explained in more detail.

Conclusions have been expanded to better explain how discretization influences the CO2 pressure and storage simulations. Furthermore, comments have been added on the significance and applicability of the proposed approach.

Reviewer 3 Report

Date: 20-10-2022

Comments

 

Reviewer:

 

Comments and Suggestions for Authors

The authors submitted an article entitled as “Gridding effects on CO2 trapping in deep saline aquifers” and explored gridding effect with substantial data. The work sounds good. Authors provided well designed work written and discussed consistently with obtained findings. The work is valuable for publication in the Journal after major revision. However, I recommend revision considering my suggestions and comments as below

Comment 1: Introduction section is too lengthy and confusing. I found relevant sentences that should be included in discussion part elsewhere in the revised manuscript. In the sentence “The experience gained from CO2 injection in many existing enhanced oil recovery (EOR) projects [1-6] as well as from operating CO2 storage sites [7- 11] indicates that it is feasible to store CO2 in geological formations as a mitigation option to climate change [12-17]”, authors cited unnecessary references. If relevant, please explain the findings from each of them. The sentences “Geological storage sites should fulfill the following conditions: the capacity to store an adequate volume of CO2, the ability to accept the injected CO2 at the rate that is supplied, the ability to contain the CO2 plume by the overlying impermeable layers, and the existence of a sufficiently stable geological setting to avoid compromising the integrity and stability of the storage site” should be shortened to avoid confusion and hard to follow up the meaning.  

Comment 2: Authors provided 5 basic methods of mechanism to store CO2 in aquifers. I recommend to remove from here and present as a table form in the revised manuscript. This would reduce the size of introduction section and easy to understand by readers.

Comment 3: A detailed source of the software (GEM-CMG software) must be provided. What was the basis for selection set parameters in the software such as thickness and other parameters?

Comment 4: Table 2 must be restructured. Table 3 needs to be removed and the values can be explained in the text body of the manuscript. Or table 2 and table 3 must be merged together. In table 5, font style is different from the text body. Please keep consistency in the manuscript.

Comment 5: The scale of figure 3 must be clearly visible to reader. Please use high resolution image for this image. Similarly, figure 8f has the same issue.

Comment 6: I found various long sentences in the manuscript. Theses sentences must be rewritten to make it short, concise and clear to reader. Moreover, there are few grammatical errors throughout the manuscript and need to be resolved in revised version of the manuscript.  

Comment 7: Rewrite the sentence “Conclusions are that a fine discretization, which is acknowledged to be needed for a reliable description of the pressure evolution during injection, is also highly recommended to obtain representative results when simulating CO2 trapping in the subsurface and thus addressing the storage safety over time”.

Comment 8: Figure 1 must be replaced with better resolution image. Readers are unable to visualize the scale. Scale colour must be black to make it more visible. The caption of figure 1 must be revised as figure 1A and figure 1B. There is no need to use left or right in the caption.  

Comment 9: Authors are recommended to include a new section for statistical analysis used during software based simulation.   

Author Response

We would like to express our sincere gratitude to the reviewers for their thorough revision of the paper and valuable suggestions to improve it.

We have addressed all the points raised by the reviewers. In the following, we provide the details of the modifications we have implemented in the revised manuscript.

We hope that now the paper can qualify for publication.

Thank you all for your time.

Best,

Alessandro, Costanzo, Christoforos, and Francesca

---

Comments and Suggestions for Authors

The authors submitted an article entitled as “Gridding effects on CO2 trapping in deep saline aquifers” and explored gridding effect with substantial data. The work sounds good. Authors provided well designed work written and discussed consistently with obtained findings. The work is valuable for publication in the Journal after major revision.

We thank the reviewer for his/her appreciation of the work.

However, I recommend revision considering my suggestions and comments as below

• Comment 1: Introduction section is too lengthy and confusing. I found relevant sentences that should be included in discussion part elsewhere in the revised manuscript.

We shortened the Introduction by moving the discussion on trapping mechanisms and the explanation of why attention was focused on solubility and trapping mechanisms in the Methodology section.

In the sentence “The experience gained from CO2 injection in many existing enhanced oil recovery (EOR) projects [1-6] as well as from operating CO2 storage sites [7- 11] indicates that it is feasible to store CO2 in geological formations as a mitigation option to climate change [12-17]”, authors cited unnecessary references. If relevant, please explain the findings from each of them.

References [1-17] were initially provided in the paper only to make the case that CO₂ injection is not a new practice. However, we agree with the reviewer that only some of them were strictly relevant. Thus, unnecessary references were eliminated.

 

The sentences “Geological storage sites should fulfill the following conditions: the capacity to store an adequate volume of CO2, the ability to accept the injected CO2 at the rate that is supplied, the ability to contain the CO2 plume by the overlying impermeable layers, and the existence of a sufficiently stable geological setting to avoid compromising the integrity and stability of the storage site” should be shortened to avoid confusion and hard to follow up the meaning.

We have rewritten the sentence and made it shorter and more to the point.

• Comment 2: Authors provided 5 basic methods of mechanism to store CO2 in aquifers. I recommend to remove from here and present as a table form in the revised manuscript. This would reduce the size of introduction section and easy to understand by readers.

The basic trapping mechanisms have been summarized in a table, as suggested by the reviewer, and moved to the Methodology section along with the explanation of why attention was focused on solubility and trapping mechanisms.

• Comment 3: A detailed source of the software (GEM-CMG software) must be provided. What was the basis for selection set parameters in the software such as thickness and other parameters?

More details and explanations regarding the model and selected parameters have been added to the Model description section.

• Comment 4: Table 2 must be restructured. Table 3 needs to be removed and the values can be explained in the text body of the manuscript. Or table 2 and table 3 must be merged together. In table 5, font style is different from the text body. Please keep consistency in the manuscript.

As suggested, Table 2 was modified; Table 3 was removed; Table 5 was edited.

• Comment 5: The scale of figure 3 must be clearly visible to reader. Please use high resolution image for this image. Similarly, figure 8f has the same issue.

We have used high-resolution images in the revised paper. Both fig. 3 and 8f should now be clearly readable.

• Comment 6: I found various long sentences in the manuscript. Theses sentences must be rewritten to make it short, concise and clear to reader. Moreover, there are few grammatical errors throughout the manuscript and need to be resolved in revised version of the manuscript.

The paper has been fully revised by a native English-speaker. Long sentences have been shortened and grammatical errors/typos have been corrected.

• Comment 7: Rewrite the sentence “Conclusions are that a fine discretization, which is acknowledged to be needed for a reliable description of the pressure evolution during injection, is also highly recommended to obtain representative results when simulating CO2 trapping in the subsurface and thus addressing the storage safety over time”.

The sentence has been rewritten to make it shorter and clearer.

• Comment 8: Figure 1 must be replaced with better resolution image. Readers are unable to visualize the scale. Scale colour must be black to make it more visible. The caption of figure 1 must be revised as figure 1A and figure 1B. There is no need to use left or right in the caption.

All the issues raised about Fig. 1 have been addressed

• Comment 9: Authors are recommended to include a new section for statistical analysis used during software based simulation.

We are afraid that there has been a misunderstanding because we did not perform any statistical analysis. We are not sure whether the reviewer means we should perform them. If this were the case, we would like to clarify that we didn’t intend to assess the “error” affecting the simulation results. Simply, we wanted to demonstrate that the model discretization affects the estimated amount of CO₂ trapped by the different mechanisms. The percentage variations we calculated are indicative as they depend on the model parameters; however, they prove that the impact of discretization can be significant.

Round 2

Reviewer 2 Report

The indicated changes have been made and are therefore proposed for publication in present form.

Reviewer 3 Report

I recommend for publishing the revised version.