Feasibility Assessment of Acid Gas Injection in an Iranian Offshore Aquifer

Round 1

Reviewer 1 Report

Injecting acidic gases, mainly carbon dioxide, into rock formations is currently a topic of concern for countries around the world. The author conducted a practical engineering study as an example, providing research on the total amount of injection, pressure, injection rate, porosity and permeability of rock formations, etc. This study is very valuable and meaningful.

In previous studies in various countries, there have been some specific engineering cases, but the relevant details have not been explained. Although there are many injection projects in various countries around the world, the relevant papers are not detailed or clear. This article has great promotional value and is also quite cutting-edge in its work. It is also recommended that this paper be published.

 

Below are a few questions that the author should pay attention to adding and modifying:

1. In Figure 5, a large number of data points are listed, which are very valuable and meaningful.

The porosity ratio greatly affects the permeability coefficient, and the influence of the porosity ratio on the permeability coefficient varies among different lithologies. However, we have also found in previous studies that the permeability coefficient is also closely related to burial depth.

Similar rocks, with different burial depths, have different porosity ratios. At the same time, under the same rock and burial depth, the porosity ratio and permeability coefficient are not completely the same. Therefore, more explanations and explanations need to be introduced.

Suggest referring to our published papers: [1], [2], [3], and adding more possible explanations.

The reason for the explanation is that during the formation process of rock layers, they may receive driving forces from groundwater, leading to changes in pore ratio.

At different depths, different pressures lead to changes in porosity, and under pressure, some unobstructed pores may experience blockage and sealing effects.

[1] Sun Jichao, Huang Yuefei Modeling the Simultaneous Effects of Particle Size and Porosity in Simulating Geo Materials Materials, 2022, 15 (4): 1576

[2] Sun Jichao Permeability of particle soils under soil pressure Transport in Porous Media, 2018, 123 (2): 257-270

[3] Sun Jichao, Wang Guangqian Transport model of underground sedimentation in soils Scientific World Journal, 2013: 367918

In Figure 5, what is the unit of the y-axis, what is the calculation formula, and the occurrence of negative values can cause misunderstandings for readers. It is necessary to provide some explanation and explanation in the figure.

 

2. Can there be more geological data on the site studied in this paper, especially the display of a geologic map of a certain length? The scale of some images in the text is missing.

3. It is recommended to accept the publication of this paper.

The paper is very valuable, and very meaningful, the workload is very good, it is recommended to accept the publication

It is nice.

Author Response

Hi, thanks for your wise and precise comments. Using your comments enables us to provide a better presentation of our paper. 

For the first comment the correction has been made to the figure and it is logarithms of permeability that now justify the negative value in the figure Also we use one of your papers and cite it properly for more explanation.

Regarding the second comment, the field is a shared reservoir, and for the confidentiality inherent in the field and due to lack of proper data it is not possible for us to share more data on the paper. hope you will be satisfied by our answer 

Reviewer 2 Report

This manuscript reports a case study investigating the effects of different factors on the feasibility of acid gas injection. The authors, however, do not present the contents in a logical way. The paper should follow a logical presentation of background, research methods, results, and conclusions. I suggest the authors rearrange the materials in Sections 2–5 to improve the readability of the paper. 

1.     The title should be “… an Iranian Offshore Aquifer (or some other words)”. Same for Line 14, it should be “… in an offshore saline aquifer”.

2.     The Abstract needs significant improvement to clearly and concisely present: (1) background/significance, (2) what is missing in the existing research, (3) what has been done in this research, (4) important results and conclusions.

3.     Please consider adding proper references in the Introduction section. Currently, only one paper is cited for an entire paragraph.

4.     Figure 2: It would be better to also label or highlight the locations of Iran and Bushehr.

5.     Lines 114–134: These two paragraphs should be placed in Introduction.

6.     Lines 145–147: What is the empirical correlation? Please include the equations and cite at least one reference.

7.     Line 208: “Temperature”

8.     Lines 216: This sentence is incomplete.

9.     Line 219: What are S_w and S_wi?

10.  Line 221: How is the λ determined? Either clarify or cite proper references.

11.  Line 230: The authors should explain how these fitting parameters are obtained.

12.  Lines 235–236: No further interpretations on Figures 8 and 9?

13.  Consider placing Figures 10 and 11 in the Results section.

14.  The font sizes in Figures 13, 14, and 18 are too small to be read.

15.  Table 3 is not shown correctly.

16.  The results are not well summarized in the Conclusions.

Author Response

thanks for your comments all your comments have been considered and applied

regarding comment 14, it is not possible to increase the size since the original figure is too large I have to shrink it to be appropriate for the manuscript.  

Reviewer 3 Report

This study aims to assess the feasibility of Acid Gas Injection (AGI) in an Iranian offshore saline aquifer. It delves into reservoir properties, geomechanics, caprock integrity, and gas plume dynamics. The manuscript identifies the Surmeh formation, characterized by upper dolomite and lower carbonate, as suitable after analyzing relevant data. Geomechanical analysis reveals pore and fracture pressures. Caprock, particularly the Hith formation, is considered vital for containment. Seismic mapping illustrates caprock thickness variations. Capillary trapping affects short-term gas entrapment and plume distribution. Numerical simulations underscore the impact of rock heterogeneity.

 

However, the overall impression from reading this manuscript suggests that it resembles more of a project plan rather than a genuine case study. This perception arises from the fact that the data presented throughout the manuscript primarily originates from existing literature or the author's own proposed data, yet lacks sufficient explanation for the rationale behind the selection of these specific parameters. The manuscript lacks concrete data obtained from practical field studies, which should ideally constitute a significant portion of its content.

 

Furthermore, a substantial portion of the article delves into the geomechanical analysis of the feasibility of CO2 injection. However, a crucial deficiency lies in the absence of a foundational introduction to the type of geomechanical model being employed, the techniques utilized, or even the constitutive model applied. These omissions raise concerns regarding the reliability of the analysis results, thus diminishing the manuscript's suitability as a case study and positioning it more as a technical report.

 

Additionally, several technical intricacies remain unexplained by the author. For instance, the manuscript highlights two distinct cases with permeability values of 1 and 0.1 mD, yet fails to elucidate the significance of these specific permeability ranges or why they were chosen as representative examples. The absence of this explanation leaves readers perplexed about the rationale behind these choices.

 

In summary, the manuscript requires significant improvements to transform it into a bona fide case study. Addressing these issues by incorporating actual field data, providing comprehensive explanations for parameter choices, offering clear insights into the geomechanical model and techniques employed, and clarifying the selection of representative cases would significantly enhance its credibility and relevance.

This part is great.

Author Response

thanks for your thoughtful comments, regarding the Geomechanical model, Since this not the relevant case of just geomechanics it has been been decided to highlight the required result for the next step of modeling. all the details on the geomechanical modeling are referenced by us in 3 papers that we published earlier. However, after your comments, we decided to add two paragraphs to bold the general procedure of the goemechanical model in this paper too. 

About the 1 ad 0. mD perm, we decided to cover the possible range of perm expected on the field to somehow bold the minimum and maximum range of perm. this study aimed to create a procedure for feasibility assessments of AGI with low cost and time consumption using all available data. with this procedure without spending too much time and energy, we find out that the formation is not suitable for the injection, hence using very limited data it is discovered what type of reserve can be nominated for such action. Considering your comments now in the manuscripts it is strictly mentioned the reason for choosing these two magnitides for modeling.

all your comments now has been appiled. 

thanks for your time.

Reviewer 4 Report

1. In general, the literatures cited in this article are not enough. Some statements cannot be reliably supported.

2. The AGI should be explained with AGI projects as examples.

3. “Case study”: What are the safety and environmental standards referred to in paragraph 1? What gases can be used to make AGI? Is there a specific reference?

 

4. The geological settings of the storage area should be given with more details.

5. Some of the diagrams are not clear, for example, some of the handwriting in Table 3 is overlapping.

6. The analysis of “Results” is abrupt and not sufficiently contextual.

7. The conclusion should be improved.

(1) this paper analyzes the feasibility of reservoir properties, geomechanical aspects, caprock integrity and gas plume dynamics. It is necessary to summarize the analysis of these factors.

(2) the results of this feasibility assessment or the author's recommendations and/or observations should be specified.

Author Response

thanks for your thoughtfull comments All you requested now has been taken care of. 

regarding comment number 4, the field is a shared reservoir, and for the confidentiality inherent in the field and due to the lack of proper data it is not possible for us to share more data on the paper. hope you will be satisfied by our answer 

Thanks for your time

Round 2

Reviewer 2 Report

The authors should at least provide a point to point response to my review comments. In the response, the authors should also indicate where the corrections are made to the revised manuscript. Now I have no idea which revisions in the revised manuscript are to address which of my comments.

Author Response

Greeting 

sorry for the inadequate response to your thoughtful comments. Now I will explain point by point.

1. The title is changed to " Feasibility Assessment of Acid Gas Injection in an Iranian Offshore Aquifer"
2. the abstract has been changed and now covers all 4 points that you mentioned earlier 
3. more references are introduced in the introduction.
4. done.
5. done.
6. figure 6 has been added to introduce the correlation,
7. changed to " formation temperature".
8. completed.
9. now they are introduced in the text.
10. cited.
11. explained in the text. For relative permeability and capillary pressure modeling, typical values of empirical correlations for carbonate formation were utilized.
12. just the visualization of the parameters was the key. 
13. with all due respect doing this correction will change the chirography and coherency of the manuscript. 
14. it is not possible to change the font size in fi 13 14 18 because the original picture was in A3 size due to the 100-year forecast and after shrinkage of the photo the best results have been selected and used.
15. corrected
16. the conclusion is now re-written.

thanks for your comments

Reviewer 4 Report

The paper is revised and can be accepted for publishment. 

Author Response

thanks for your suggestion 

Round 3

Reviewer 2 Report

No further comments