Investigating Asphaltene Precipitation and Deposition in Ultra-Low Permeability Reservoirs during CO₂-Enhanced Oil Recovery

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

Article "Investigating Asphaltene Precipitation and Deposition in Ultra-low Permeability Reservoirs During CO₂ Flooding to Enhance Oil Recovery" is devoted to the asphaltene precipitation. The article is formatted extremely sloppily, so it makes sense to review it only after it has been completely revised. I consider this a complete disrespect for the reviewers and the editor. Here are some of the limitations I saw in the abstract and introduction:

1) First of all, you need to correctly format references to literary sources - in square brackets with automatic links.

2) line 7- «CO2»

3) line 9 – “may cause” font is different from the rest of the text

4) line 18 – “the” must be capitalized

5) lines 46, 63 and 77 – extra space

There are a lot of such limitations throughout the work - starting with gross mistakes, ending with sloppy signatures on the drawings, etc. I don’t consider it necessary to consider the scientific part of the work until all these limitations are corrected, therefore I cannot judge the value of the work at the current moment.

Author Response

Dear reviewer,

We tried our best to improve the manuscript and made some changes to the manuscript. These changes will not influence the content and framework of the paper. Here we did not list the changes but marked them in red in the revised paper. We appreciate for Reviewers’ warm work earnestly and hope that the correction will meet with approval.

1) First of all, you need to correctly format references to literary sources - in square brackets with automatic links.

We were really sorry for our careless mistakes. Thank you for your reminder.

2) line 7- «CO2»

We feel sorry for our carelessness. In our resubmitted manuscript, the type is revised

3) line 9 – “may cause” font is different from the rest of the text

We were really sorry for our careless mistakes.Thank you for your reminder.

4) line 18 – “the” must be capitalized

We were really sorry for our careless mistakes.Thank you for your reminder.

5) lines 46, 63 and 77 – extra space

We feel sorry for our carelessness. In our resubmitted manuscript, the type is revised.

Again, thank you for allowing us to strengthen our manuscript.

Best regards,

Dandan Yin, Qiuzi Li, and Dongfeng Zhao

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

1. Is the core sample used in this manuscript from Block X in the Ordos Basin universally representative? Is the conclusion drawn only applicable to this block?

2. How does SARA affect asphalt precipitation? Is there further research and is there a critical value at which SARA affects asphalt precipitation?

3. There are two Figure 1 in the manuscript.

4. Figure 3 lacks a length scale.

5. Figure 3 shows the observation results of Sigma Scan Pro 5, but black spot recognition method was used to identify the amount of asphalt precipitation. But what is the recognition effect of its software? For example, in Figure 3h, 62.12% of the areas were identified as asphalt precipitates. Is there a phenomenon of recognizing shadows in photos as asphalt precipitation?

6. Is there a three-dimensional overlap phenomenon in the spots in Figure 3 that affects the calculation results?

7.From the Figure, when the pressure increases to 13MPa (Figure 8(b)) , the reduction of large pores is not very obvious. What is the difference in signal amplitude in terms of numerical values?

8. Author believes that the significant difference in signal amplitude before and after flooding is due to the oil in the large pore-throat (10-100 ms) is easier to drive out during immiscible flooding. Please provide more evidence to support this, such as comparing relevant numerical values.

9. Is there any experimental or theoretical basis for Conclusion 3? Please supplement.

Author Response

Dear reviewer,

We sincerely appreciate your time and effort invested in evaluating our manuscript. According to your nice suggestions, we have made extensive corrections to our previous draft, the detailed corrections are listed below.

1. Is the core sample used in this manuscript from Block X in the Ordos Basin universally representative? Is the conclusion drawn only applicable to this block?

Block X in the Ordos Basin in the manuscript is the largest low-permeability oilfield block from China, which is a typical ultra-low permeability reservoir. The conclusions drawn are also applicable to other ultra-low permeability fields.

2. How does SARA affect asphalt precipitation? Is there further research and is there a critical value at which SARA affects asphalt precipitation?

In the paper named “Asphaltene Deposition during CO2 Injection and Pressure Depletion:

A Visual Study”， a comparison of two different asphaltene sources in terms of aggregation and flocculation behavior revealed that the asphaltene molecular structure could have a noticeable influence on asphaltene deposition. The differences in asphaltene molecular structures could be one of the main factors affecting asphaltene aggregation, deposition, and size distribution. However, it is not determined clearly because of the complex nature of asphaltene molecules. We are currently studying the effect of asphaltene structure on precipitation using crude oil with four different asphaltene compositions, but no rules have been obtained.

3. There are two Figure 1 in the manuscript.

Thanks for your careful checks. We are sorry for our carelessness. Based on your comments, we have made the corrections in the manuscript.

4. Figure 3 lacks a length scale.

We feel sorry for our carelessness. In our resubmitted manuscript we added a length scale in Figure3. 

5. Figure 3 shows the observation results of Sigma Scan Pro 5, but the black spot recognition method was used to identify the amount of asphalt precipitation. But what is the recognition effect of its software? For example, in Figure 3h, 62.12% of the areas were identified as asphalt precipitates. Is there a phenomenon of recognizing shadows in photos as asphalt precipitation?

Sigma Scan Pro5 can realize complex image analysis and data processing. Sigma Scan Pro's enhancement technology improves image quality and removes some excess parts. We can set the threshold value to identify and count the area of different depths of color, and you can filter out the shadow of the light color part.

6. Is there a three-dimensional overlap phenomenon in the spots in Figure 3 that affects the calculation results?

 The geometric properties of asphaltene aggregation were determined by analyzing the captured images using Sigma Scan Pro 5 software. The software provides a shadow removal function that can automatically identify and remove shadows from an image. These tools typically use sophisticated algorithms to analyze the brightness and contrast of an image and thus distinguish between shaded and non-shaded areas. In some cases, image processing techniques alone may not be able to accurately distinguish shaded parts. At this point, it is necessary to combine manual judgment, manually mark the shaded area, or use other methods to assist in discrimination.

7. From the Figure, when the pressure increases to 13MPa (Figure 8(b)), the reduction of large pores is not very obvious. What is the difference in signal amplitude in terms of numerical values?

The T2 value and the corresponding signal amplitude represent the size and number of pore Spaces in which the hydrogen core is located, so the T2 spectrum can be converted into the core pore radius distribution. When the pressure increases to 13MPa (Figure 8(b)), the T2 signal of the large pores does not weaken much. The cores of the two NMR measurements were the same section core, and the error was small. According to the above visualized experimental results (Figure 3(c)), the asphaltenes at this time only slightly aggregated and appeared as spots, mainly in the form of adsorption, and the relative deposition of asphaltenes at this time was also relatively small, about 12.6%, which had a weak influence on the large pores. The displacement behaviors (Figure 8(b)) were consistent with visualization observations in Figure 3(c).

8. Authors believe that the significant difference in signal amplitude before and after flooding is due to the oil in the large pore-throat (10-100 ms) is easier to drive out during immiscible flooding. Please provide more evidence to support this, such as comparing relevant numerical values.

I have added a comparison of T2 response measured for the initial oil-saturated core and that measured for the core immediately after CO2 flooding at the back pressures of 8 MPa, 13 MPa, 16 MPa, and 20 MPa respectively, in the resubmited manuscript. The area covered by the T2 response stands for the relative oil contents in the core. The difference in T2 frequency represents the change in oil content in pores of different sizes before and after CO2 displacement, clearly reflecting where the oil was recovered.

9. Is there any experimental or theoretical basis for Conclusion 3? Please supplement.

 Comparison of T2 response measured for the initial oil-saturated core and that measured for the core immediately after CO2 flooding could support conclusion 3.

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

The manuscript is on the effect of asphaltene deposition in tight reservoir system in Carbon capture storage and utilization (CCSU). The idea is well known in that the impact of deposition would be more severe in ultra low permeability reservoir rocks however, its great an attempt is made to establish the level of damage. However, some pertinent question must be addressed to improve the manuscript. Thus, I recommend a Minor revision.

(1) Most of the references cited are from before 2017. Lack of references for the last three years. The authors need to cite and discuss these references in the introduction and emphasize the novelty of this work.

(2) Abstract: “nuclear magnetic resonance, which quantitatively…different pressures.” Kindly check the grammar here. It is incorrect.

(3) The Materials section needs to be clearly written. All the chemical materials should provide the purity and sources.

(4) Abstract: “nuclear magnetic resonance, which quantitatively…different pressures.” Kindly check the grammar here. It is incorrect.

(5)  “living” it should be live oil not living oil.

(6) In Figure 3, Given the limitation of visual technique for detecting asphaltene onset and the fact that nanoaggregate cannot be detected by the eye, how certain are at the authors about the 12.6 Mpa as onset pressure? This is because even a microscope has the limitation that asphaltene must grow to its detection limit before it can be detected. Thus, kindly clarify.

（7）" Performance Evaluation of CO2 Soaking and Flooding Processes in Tight Oil Reservoirs" could be read and referred.

 

 

 

Comments on the Quality of English Language

Quality of English Language is good.

Author Response

(1) Most of the references cited are from before 2017. Lack of references for the last three years. The authors need to cite and discuss these references in the introduction and emphasize the novelty of this work.

Thanks for your suggstion, I will add Research Status in recent years.

(2) Abstract: “nuclear magnetic resonance, which quantitatively…different pressures.” Kindly check the grammar here. It is incorrect.

I will check and correct such mistakes. Thank you for pointing out

(3) The Materials section needs to be clearly written. All the chemical materials should provide the purity and sources.

Thanks for your kindly remind. I will supple the purity and sources of all experimental materials.

(4) Abstract: “nuclear magnetic resonance, which quantitatively…different pressures.” Kindly check the grammar here. It is incorrect.

I will check and correct such mistakes. Thank you for pointing out

(5)  “living” it should be live oil not living oil.

I will check and correct such mistakes. Thank you for pointing out

(6) In Figure 3, Given the limitation of visual technique for detecting asphaltene onset and the fact that nanoaggregate cannot be detected by the eye, how certain are at the authors about the 12.6 Mpa as onset pressure? This is because even a microscope has the limitation that asphaltene must grow to its detection limit before it can be detected. Thus, kindly clarify.

Sigma Scan Pro5 can realize complex image analysis and data processing. Sigma Scan Pro's enhancement technology improves image quality and removes some excess parts.

（7）" Performance Evaluation of CO2 Soaking and Flooding Processes in Tight Oil Reservoirs" could be read and referred.

Thanks for your suggestions, I will add the references.

Author Response File: Author Response.pdf

Reviewer 4 Report

Comments and Suggestions for Authors

Asphaltene precipitation is a common problem during CO2 injection, as it can cause reservoir damage. Asphaltene is a substance in crude oil that is insoluble in low molecular weight n-alkanes but soluble in benzene and toluene. Experiments reveal the mechanism of pore-scale reservoir damage caused by asphaltene precipitation during CO2 injection in ultra-low permeability reservoirs.The article has certain reference value.

But in my opinion, there are some problems in the article for reference.

1. The manuscript presents detailed experimental procedures and findings related to asphaltene deposition during CO2 flooding. However, the mechanisms by which asphaltenes affect the reservoir's properties could be elaborated further. Specifically, it would be beneficial to provide a clearer explanation of how asphaltene precipitation impacts the oil recovery processes at different pressures, particularly in the miscible and immiscible phases.

2. While the manuscript provides extensive data and graphical illustrations, some figures (e.g., Figures 3 and 8) could be enhanced with higher resolution or better labeling for clarity. This will help in effectively conveying the changes observed at different pressures and the corresponding impacts on the reservoir's properties.

3. The description of the experimental setup and the methodologies used are comprehensive. However, the manuscript would benefit from a more detailed explanation of the selection criteria for the core samples and the specific conditions under which experiments were performed. Clarifying these choices would strengthen the replicability of the study.

 

The paper may be published in your journal after the above revisions completed.

Comments on the Quality of English Language

1.The manuscript is generally well-written but could benefit from minor revisions to improve clarity and flow. Some sentences are overly complex or contain redundant words, which could potentially confuse readers."Suggestion: "Consider simplifying complex sentences and removing unnecessary words to enhance readability."

2.Suggestion: "I recommend a thorough grammatical review. For example, on page 2, 'the concentration of resins as an asphaltene stabilizer is further reduced,' could be rephrased for better clarity."

3.Comment: "The manuscript frequently uses passive voice, which can make sentences longer and harder to read."

Suggestion: "Consider using active voice where appropriate to make sentences clearer and more dynamic."

Author Response

Dear reviewer，

Thank you for your comments concerning our manuscript. Those comments are valuable and very helpful. We have read through the comments carefully and have made corrections. Based on the instructions, we uploaded the file of the revised manuscript. 

We would love to thank you for allowing us to resubmit a revised copy of the manuscript and we highly appreciate your time and consideration.

Sincerely.

Dandan Yin Qiuzi Li and Dongfeng Zhao

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Unfortunately, the authors did not work on the artiсle even on those typos that I indicated, not to mention the entire text. I consider this an extreme degree of disrespect. Therefore the work should be rejected.

Author Response

Dear reviewer，

Thank you for your comments concerning our manuscript. Those comments are valuable and very helpful. We have read through the comments carefully and have made corrections. Based on the instructions, we uploaded the file of the revised manuscript. 

Best regards,

Dandan Yin, Qiuzi Li and Dongfengzhao

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Comments and Suggestions for Authors

The authors have done enough work on the article, so it can be published in its current form