A Critical Review Using CO₂ and N₂ of Enhanced Heavy-Oil-Recovery Technologies in China

Round 1

Reviewer 1 Report

See attached file.

Comments for author File: Comments.pdf

Author Response

Dear Editors and Reviewers,

    Thank you very much for your helpful comments and suggestions. According to your comments of reviewers and editor, we have carefully and meticulously revised the manuscript (applsci-1963203), and responded, point by point to the comments mentioned. The revised parts are highlighted in red, and the amendments and deleted contents are marked with the gray strike-out font.

Reviewer #1:

The intellectual merit of the paper is missing. Overall, the reader is left to wonder what the objective of this ‘critical review’ is, and the deficiency in the literature that the paper seeks to address and fill.

[Comment 1]: Adding to the points raised in the foregoing, it is questionable as to whether the paper is actually a ‘critical’ review. Where is the critique? It is the reviewer’s opinion that the authors fail to point out any aberrations, omissions, flaws, points of inclarity, or any defects in the literature. Furthermore, the observations stated in the section on future prospects are obvious. Thus, it is not clear as to what value this work adds to the corpus of work available.

[Reply 1]: First of all, this paper discusses the shortcomings of the existing heavy oil thermal recovery technology, that is, steam recovery. To improve the production effect, this paper summarizes the existing research and conclusions of non-condensable gas injection. Secondly, we only investigated existing development technologies with potential in the future. This paper has no innovation in new heavy oil recovery technology.

[Comment 2]: It seems that the authors are focusing on steam injection as the enhanced heavy-oil recovery technology (and for good reason). Thus, the title should specifically state that, instead of the EOR generalization.

[Reply 2]: Steam injection is indeed a key thermal recovery technology for heavy oil recovery. However, due to the shortcomings of this technology in the late stage of recovery, it is proposed to inject non-condensable gas to improve recovery.

[Comment 3]: There are several statements made (e.g. last line in the first paragraph of page 3; penultimate sentence of the 2nd paragraph of page 3; first sentence in page 7; penultimate line of the first paragraph in Section 4.1; first sentence in 2nd paragraph of Section 4.1 that do not have the due citations. Authors also use some figures (e.g. Figures 4, 5) that appear not to be theirs, and yet they are presented without references in the captions!

[Reply 3]: Given the above problems, we have made corresponding modifications to the contents not quoted in the text. Figures 4 and 5 are further explained and quoted in the original text.

[Changes]: Please see Lines 10~12 on Page 3, Line 19~20 on Page 3, Line 19~20 on Page 7, Line 22~24 on Page 7, Line 16~17 on Page 9, Line 19~21 on Page 9, Line 22~23 on Page 9, Line 25~26 on Page 9, Line 22~26 on Page 13, in the "Revision, changes marked".

[Comment 4]: The authors state that there are many kinds of non-condensate gases without even stating examples. It is not sufficient to merely say that the focus is on N₂ and CO₂ because it is common, and yet preserves a generalized article title.

[Reply 4]: There are many types of non-condensable gas, including CO₂, N₂, CH₄, and flue gas. The main components of the flue gas are N₂ and CO₂. CH₄ is not normally used for oil exploitation. Therefore, this paper focuses on the common CO₂ and N₂, which are cheap and easy to obtain.

[Changes]: Please see Lines 9~11 on Page 2, in the "Revision, changes marked".

[Comment 5]: It is not clearly stated why the authors chose to treat non-condensate gas usage separately. Doing this in addition to the treatment with EOR made the review repetitive. The reviewer suggests that the review should be focused on non-condensate gas EOR.

[Reply 5]: In the introduction of this paper, the difficulties faced by steam flooding in the later stage of the development of thermal recovery technology are introduced. Non-condensate gas-assisted steam flooding technology is a very promising technology. This paper has indeed focused on CO₂ and N₂ EOR.

Other Comments

[Comment 1]: Reference [86] could not be verified.

[Reply 1]: Thank you for your careful review. We have revised the reference [86].

[Changes]: Please see Lines 16~17 on Page 23, in the "Revision, changes marked".

[Comment 2]: It is not clear why section 2 is in the text. To promote coherency, the authors may want to consider stating the structure of the manuscript, and providing some justification for the sections.

[Reply 2]: The purpose of the second section is to analyze the adaptability of injecting non-condensate gas into heavy oil reservoirs. This section lays a good foundation for the development of the following review.

[Comment 3]: There are several sentences that need to be either clarified or rephrased. The following are only some examples:

[Comment 3 a]: First sentence in Section 1 should be qualified as to whether the 20% of the total oil resources are global or in China.

[Reply 3 a]: Thank you for your careful review. The first sentence in Section 1 qualified as to whether the 20% of the total oil resources in China.

[Changes]: Please see Lines 25 on Page 1, in the "Revision, changes marked".

[Comment 3 b]: Fifth sentence in Section 1 should be rephrased.

[Reply 3 b]: Thanks for your valuable suggestion. Heavy oil recovery technology includes hot recovery and cold production. The main recovery methods of hot recovery and cold production are briefly introduced respectively.

[Changes]: Please see Lines 29~32 on Page 1, in the "Revision, changes marked".

[Comment 3 c]: Last sentence in paragraph 1 of Section 1 should be clarified.

[Reply 3 c]: We restated the causal relationship of the sentence. Because the problems faced in the late development period need to be solved and new replacement technologies need to be found, experimental research and field practice of non-condensable gas injection has been carried out.

[Changes]: Please see Lines 3~5 on Page 2, in the "Revision, changes marked".

[Comment 3 d]: First sentence in paragraph 2 of Section 1 should be clarified.

[Reply 3 d]: There are many kinds of non-condensate gases, including CO₂, N₂, CH₄, and flue gas. The main components of the flue gas are N₂ and CO₂. CH₄ is not commonly used in petroleum exploitation. Therefore, common types of gases include N₂ and CO₂ due to abundant gas sources and lower prices.

[Changes]: Please see Lines 9~11 on Page 2, in the "Revision, changes marked".

[Comment 3 e]: The allusion to Figure 2 in the text should be clarified.

[Reply 3 e]: The non-condensable gas injected in the SAGD production process is SAGP (Steam and Gas Push). Compared with traditional SAGD, adding non-condensable gas can maintain the effective expansion of a mature SAGD steam chamber, which will have higher oil displacement efficiency. Figure 2, shows the development of the steam cavity after injecting non-condensate gas during the SAGD development of a heavy oil reservoir.

[Changes]: Please see Lines 24~28 on Page 2, in the "Revision, changes marked".

[Comment 3 f]: Second sentence in Section 3 should be rephrased.

[Reply 3 f]: However, some heavy oil reservoirs are thin formations. When steam injection information, the heat loss of the formation is large, and the dryness of steam decreases rapidly, which leads to the insufficient application of heat.

[Changes]: Please see Lines 28 on Page 3 and Lines 1~2 on Page 4, in the "Revision, changes marked".

[Comment 3 g]: The first sentence in Section 3.1 should be broken down for clarity.

[Reply 3 g]: Thanks for your valuable suggestion. Many researchers have conducted experiments of enhanced heavy oil recovery studies using CO₂, and suggest that CO₂ has a significant effect. This manuscript mainly focuses on the EOR technology of heavy oil reservoirs, so the application of CO₂ in other types of oilfields is not explained in detail.

[Changes]: Please see Lines 10~11 on Page 4, in the "Revision, changes marked".

[Comment 3 h]: Second sentence in the 2nd paragraph of Section 3.2 requires much more clarity.

[Reply 3 h]: The Yanlin Oilfield in China was introduced in more detail. After the N₂ injection in the north area of Yanling Oilfield, the oil-water interface decreased, the comprehensive water cut decreased, and the output increased. The annual oil production for nine consecutive years was higher than that before the N₂ injection.

[Changes]: Please see Lines 26~31 on Page 7, in the "Revision, changes marked".

[Comment 4]: The acronym EOR first shows up without proper statement as to what it is. Authors should state what EOR is fully (at least initially).

[Reply 4]: The abbreviation EOR stands for enhanced oil recovery. We explained the location where EOR first appeared in this paper.

[Changes]: Please see Lines 5 on Page 6, in the "Revision, changes marked".

[Comment 5]: The reviewer suggests strongly that sentences should not begin with “and” (2^nd sentence in 2^nd paragraph of page 6).

[Reply 5]: Thank you for your careful review. We have revised this.

[Changes]: Please see Lines 14 on Page 6, in the "Revision, changes marked".

Author Response File: Author Response.pdf

Reviewer 2 Report

Manuscript title: A critical review using non-condensate gas of enhanced heavy-oil-recovery technologies

The manuscript is a good attempt to gather information about application prospects in the future of oil recovery and energy utilization. However, some improvements are required before publication.

1. The English structure of the abstract needs to be improved since a number of sentences are vague.

2. The SAGD production technology in introduction should be better discussed and improved.

3. Figure 7 (Non-condensable gas displacement) can be more detailed and its quality should be enhanced.

4. The conclusion is written well, future prospects must be included more.

Author Response

Reviewer #2:

The manuscript is a good attempt to gather information about application prospects in the future of oil recovery and energy utilization. However, some improvements are required before publication.

[Comment 1]: The English structure of the abstract needs to be improved since a number of sentences are vague.

[Reply 1]: Aiming at the vague sentence expression, the abstract is modified and adjusted.

[Comment 2]: The SAGD production technology in introduction should be better discussed and improved.

[Reply 2]: First, we explain the position where SAGD first appeared. Secondly, the non-condensable gas injected in the SAGD production process is SAGP (Steam and Gas Push). Compared with traditional SAGD, adding non-condensable gas can maintain the effective expansion of a mature SAGD steam chamber, which will have higher oil displacement efficiency. Figure 2, shows the development of the steam cavity after injecting non-condensate gas during the SAGD development of a heavy oil reservoir.

[Changes]: Please see Lines 22 on Page 2, Lines 24~28 on Page 2, in the "Revision, changes marked".

[Comment 3]: Figure 7 (Non-condensable gas displacement) can be more detailed and its quality should be enhanced.

[Reply 3]: First, modify Figure 7. Add rock and sand grains after being corroded by CO₂. Secondly, the phenomenon is described. That is, after the non-condensate gas is injected into the formation, it dissolves the rock and increases the seepage space.

[Changes]: Please see Lines 16 on Page 15, Lines 12~14 on Page 15, in the "Revision, changes marked".

[Comment 4]: The conclusion is written well, future prospects must be included more.

[Reply 4]: Thanks for your valuable suggestion. We have supplemented the future outlook. Long-term steam injection development has resulted in many problems, such as steam channeling between wells, changes in physical properties of gasoline injection reservoirs, changes in crude oil properties during thermal recovery, and intrusion of edge and bottom water bodies. At present, according to the field application, the thermal composite development mode will be the key technology to realize the high-efficiency development of conventional heavy oil reservoirs in the late stage of steam thermal recovery and hard-to-produce heavy oil reservoirs. In addition, it also includes many other new technologies, such as electrical methods, electromagnetic (EM) heating, solar energy, and nuclear energy, etc. Among many technologies, the mixed process is always the most promising and easy-to-operate heavy oil production technology.

[Changes]: Please see Lines 28~31 on Page 16, Lines 34 on Page 16 and Lines 1~2 on Page 17, Lines 5~12 on Page 17, in the "Revision, changes marked".

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Ms. No.: Applsci-1963203

Title: A critical review using non-condensate gas of enhanced heavy-oil-recovery technologies

Xujiao He , Liangdong Zhao , Xinqian Lu , Fei Ding , Zijian Wang , Ruijing Han , Pengcheng Liu

Overview and General Recommendation

The authors present an overview of the use of C0₂ and N₂ as non-condensate gases in enhanced oil recovery (EOR). The specific EOR method considered is that of steam injection. To this end, various mechanisms, including those associated with the loss of heat, interfacial tension reduction, the removal of blockage, and the replenishment of formation energy are reviewed.

This reviewer re-echoes the point that while the topic looks reasonable and potentially valuable, the paper is still deficient.  Although the authors have tried to clarify the document with corrections, several flaws pointed out in the initial review have still not been corrected. Other errors also remain. These are outlined in the following comments:

Comments

      The intellectual merit of the paper is still missing. The objective of this ‘critical review’- i.e. the deficiency in the literature that the paper seeks to address and fill, is still unclear. The reviewer is obviously not expecting anything novel from a review paper. However, the authors must state the purpose of this review in the text; and specifically, why such a review is important in this specific niche of the literature.

-       If the evaluation component of the literature is done in Section 6.2, then it is still inadequate, as it stands. It is therefore still unclear as to what value this work adds to the corpus of work available, apart from being a commentary. The authors should seek to satisfy the ‘critical’ nature of the review article, as promised in its title.

-       The review is heavily skewed towards China. This does not do enough justice to the fact that 80% of heavy oil resources exist elsewhere. If the authors want to focus on China, this reviewer suggests that they make that clear in their introduction or title, or explain why this work is tilted towards works conducted in China.

-       The reviewer still suggests that the authors modify the title to show that they are only discussing N₂ and CO₂ non-condensate gases (and for good reason).

-       It is troubling to see that there are still some swathes of text / figures that require citations that are not there (lines are based on revisions presented in Word document):

·       Lines 8 – 10 of page 6.

·       Lines 19 – 22, 24 – 26 of page 8.

·       Lines 10 – 14; 28 – 30; 31- 32 of page 9.

·       Lines 13 – 14 of page 11.

·       Authors refer to a lot of researchers / scholars /works, but only cite one study e.g. Lines 26 – 27 of page 7; Lines 24 – 25 of page 9. The claims seem incongruent with the number of citations.

·       If Figures 4 and 5 are not original to the authors, they MUST be properly referenced.

Other Comments

There are several sentences that need to be either clarified rephrased, or broken down into clearer parts. The following are only some examples (lines are based on revisions presented in Word document):

a.     Sentence in line 8 – 10 of page 6 needs work.

b.     Sentences in lines 11 – 15, page 6, lines 14- 17 of page 12, and lines 6 – 8 of page 13 seem too long. They may be broken down for clarity.

c.     Lines 17, 18 of page 7 uses adjectives like “extremely” and “ordinary”. This should be qualified e.g. with magnitudes of viscosity.

d.     Tenses in line 20 (page 7), 18 -19 (page 9) need work.

e.     Shouldn’t all the main points in Section 5.2 be boldened as done for Section 5.1?

f.      Sentence in lines 1-2 of page 16 needs work.

g.     Sentence in line 26 of page 16 is not complete.

h.     Section 6 needs a prefatory statement.

Comments for author File: Comments.pdf

Author Response

Dear Editors and Reviewers,

    Thank you very much for your helpful comments and suggestions. According to your comments of reviewers and editor, we have carefully and meticulously revised the manuscript (applsci-1963203), and responded, point by point to the comments mentioned the page. The revised and added parts are highlighted with yellow emphasis, the deleted contents is marked with gray strike-out font to highlight deleted sections (lines are based on revisions presented in Word document).

Reviewer #1:

The intellectual merit of the paper is still missing. The objective of this ‘critical review’-i.e. the deficiency in the literature that the paper seeks to address and fill, is still unclear. The reviewer is obviously not expecting anything novel from a review paper. However, the authors must state the purpose of this review in the text; and specifically, why such a review is important in this specific niche of the literature.

[Comment 1]: If the evaluation component of the literature is done in Section 6.2, then it is still inadequate, as it stands. It is therefore still unclear as to what value this work adds to the corpus of work available, apart from being a commentary. The authors should seek to satisfy the ‘critical’ nature of the review article, as promised in its title.

[Reply 1]: Thank you very much for your careful reading and opinions. In view of the future outlook of Section 6.2, we have made a big revision. It is divided into non-condensate gas prospect and new technology prospect. According to a series of problems in the later stage of steam huff and puff and the shortcomings of the existing technology, the prospect is made. The composite technology of non-condensate gas and heat is the most promising at present, and it is also a subject that our researchers need to continue to study in the future. As we haven't done much research on these problems, we only made a general statement.

[Changes]: Please see Lines 3~53 on Page 16 and Line 1~9 on Page 17, in the "Revision, changes marked".

[Comment 2]: The review is heavily skewed towards China. This does not do enough justice to the fact that 80% of heavy oil resources exist elsewhere. If the authors want to focus on China, this reviewer suggests that they make that clear in their introduction or title, or explain why this work is tilted towards works conducted in China.

[Reply 2]: Thank you very much for your advice. But this article really only focuses on China's heavy oil resources. In the introduction, we have explained that China's onshore heavy oil resources are about 4 billion tons, accounting for more than 20% of China's total oil resources.

[Comment 3]: The reviewer still suggests that the authors modify the title to show that they are only discussing N₂ and CO₂ non-condensate gases (and for good reason).

[Reply 3]: Thank you very much for your advice. According to your suggestion, we change the non-condensable gas in the title to N₂ and CO₂.

[Changes]: Please see Lines 1~2 on Page 1, in the "Revision, changes marked".

[Comment 4]: It is troubling to see that there are still some swathes of text / figures that require citations that are not there (lines are based on revisions presented in Word document):

[Comment 4.1]: Lines 8-10 of page 6.

[Reply 4.1]: Thank you for your careful review. We added references here.

[Changes]: Please see Lines 11 on Page 6, in the "Revision, changes marked".

[Comment 4.2]: Lines 19-22, 24-26 of page 8.

[Reply 4.2]: Thank you for your careful review. However, literature [38] covers all the contents of this paragraph, so there is no need to repeat the quotation. Lines 24-26 of page 8, the source of this paragraph is from literature [52, 53]. Since the marking is not clear, literature [52] is moved to the previous sentence.

[Changes]: Please see Lines 15 on Page 8, in the "Revision, changes marked".

[Comment 4.3]: Lines 10-14; 28-30; 31-32 of page 9.

[Reply 4.3]: Thank you for your careful review.

Lines 10-14 of page 9: But it is true that only "The application of air, N₂, CO₂, flue gas and other non-condensate gases to assist steam flooding can achieve the purpose of further enhanced oil recovery" is quoted here. See [57] for references.

Lines 28-30 of page 9: “Many scholars have also summarized and analyzed the oil displacement mechanism in the process of CO₂-assisted steam flooding” This sentence shows the research of many scholars, citing the literature on the research results. Does not match the content. Therefore, the literature will be moved to the back of this sentence.

Lines 31-32 of page 9: References have been cited in the previous sentence, which expresses the explanation of the previous sentence's research results.

[Changes]: Please see Lines 17 on Page 9, in the "Revision, changes marked".

[Comment 4.4]: Lines 13-14 of page 11.

[Reply 4.4]: Thank you for your careful review. We split the references we put together.

[Changes]: Please see Lines 9 on Page 11, in the "Revision, changes marked".

[Comment 4.5]: Authors refer to a lot of researchers / scholars /works, but only cite one study e.g. Lines 26-27 of page 7; Lines 24-25 of page 9. The claims seem incongruent with the number of citations.

[Reply 4.5]: Thank you for your careful review.

Lines 26-27 of page 7: Here, we want to express that gas injection has been applied to low permeability reservoirs, fracture cavern carbonate reservoirs, tight reservoirs, heavy oil reservoirs, fault block reservoirs and other reservoirs, so we have referred to many literatures.

Lines 24-25 of page 9: According to the original content, we have deleted the literature.

[Changes]: Please see Lines 16 on Page 9, in the "Revision, changes marked".

[Comment 4.6]: If Figures 4 and 5 are not original to the authors, they MUST be properly referenced.

[Reply 4.6]: Figures 4 and 5 are not our original works. References are marked when cited in Figures 4 and 5.

[Changes]: Please see Lines 6 on Page 13, in the "Revision, changes marked".

Other Comments

There are several sentences that need to be either clarified rephrased, or broken down into

clearer parts. The following are only some examples (lines are based on revisions presented

in Word document):

[Comment a]: Sentence in line 8-10 of page 6 needs work.

[Reply a]: Thank you for your careful review. We have revised this sentence.

[Changes]: Please see Lines 9~11 on Page 6, in the "Revision, changes marked".

[Comment b]: Sentences in lines 11-15, page 6, lines 14-17 of page 12, and lines 6-8 of page 13 seem too long. They may be broken down for clarity.

[Reply b]: Thanks for your valuable suggestion. These sentences are really too long. We split them.

[Changes]: Please see Lines 17~23 on Page 6, Lines 1~4 on Page 12 and Lines 38~41 on Page 13, in the "Revision, changes marked".

[Comment c]: Lines 17, 18 of page 7 uses adjectives like “extremely” and “ordinary”. This should be qualified e.g. with magnitudes of viscosity.

[Reply c]: Thank you for your careful review. We have corrected the “extremely” heavy oil and “ordinary” heavy oil. “Extremely” heavy oil refers to the viscosity range of 10000 to 50000 mPa·s. “Ordinary” heavy oil refers to the viscosity range of 100 to 10000 mPa·s.

[Changes]: Please see Lines 12-15 on Page 7, in the "Revision, changes marked".

[Comment d]: Tenses in line 20 (page 7), 18 -19 (page 9) need work.

[Reply d]: We have revised the state of affairs in these two sentences.

[Changes]: Please see Lines 21~23 on Page 7 and Lines 4~6 on Page 9, in the "Revision, changes marked".

[Comment e]: Shouldn’t all the main points in Section 5.2 be boldened as done for Section 5.1?

[Reply e]: You are absolutely right. Due to our negligence, we forgot to bold the subheadings in Section 5.2. I'm very sorry here.

[Changes]: Please see Lines 51 on Page 12, Lines 16 on Page 13, Lines 9 on Page 14 and Lines 21 on Page 14, in the "Revision, changes marked".

[Comment f]: Sentence in lines 1-2 of page 16 needs work.

[Reply f]: We have improved this sentence.

[Changes]: Please see Lines 25~27 on Page 15, in the "Revision, changes marked".

[Comment g]: Sentence in line 26 of page 16 is not complete.

[Reply g]: Thank you for your careful review. We have supplemented this sentence.

[Changes]: Please see Lines 21~23 on Page 16, in the "Revision, changes marked".

[Comment h]: Section 6 needs a prefatory statement.

[Reply h]: Thank you for your valuable advice. We added a prefatory statement to section 6.

[Changes]: Please see Lines 2~7 on Page 15, in the "Revision, changes marked".

Author Response File: Author Response.pdf

Round 3

Reviewer 1 Report

Ms. No.: Applsci-1963203

Title: A critical review using non-condensate gas of enhanced heavy-oil-recovery technologies

Xujiao He , Liangdong Zhao , Xinqian Lu , Fei Ding , Zijian Wang , Ruijing Han , Pengcheng Liu

Overview and General Recommendation

The authors present an overview of the use of C0₂ and N₂ as non-condensate gases in enhanced oil recovery (EOR). The specific EOR method considered is that of steam injection. To this end, various mechanisms, including those associated with the loss of heat, interfacial tension reduction, the removal of blockage, and the replenishment of formation energy are reviewed.

Some of the issues noted in the previous review have been corrected. However, there are still some outstanding:

Comments

      The authors should provide a statement or two in the introductory section that outline the purpose of this review in the text; and specifically, why such a review is important in this specific niche of the literature.

-          The review is heavily skewed towards China. The authors must therefore state this clearly/ explicitly in their introduction or even title.

-          Figures 4 and 5 are not properly cited.  The citations MUST appear in their captions.

-          The prefatory statement (introductory or summary statement before bulleted points) is still missing.

Comments for author File: Comments.pdf

Author Response

Dear Editors and Reviewers,

Thank you very much for your helpful comments and suggestions. According to your comments of reviewers and editor, we have carefully and meticulously revised the manuscript (applsci-1963203), and responded, point by point to the comments mentioned the page. The revised and added parts are highlighted with yellow emphasis, the deleted contents are marked with gray strike-out font to highlight deleted sections (lines are based on revisions presented in Word document).

Reviewer #1:

The authors present an overview of the use of CO2 and N2 as non-condensate gases in enhanced oil recovery (EOR). The specific EOR method considered is that of steam injection. To this end, various mechanisms, including those associated with the loss of heat, interfacial tension reduction, the removal of blockage, and the replenishment of formation energy are reviewed.

Some of the issues noted in the previous review have been corrected. However, there are still some outstanding:

[Comment 1]: The authors should provide a statement or two in the introductory section that outline the purpose of this review in the text; and specifically, why such a review is important in this specific niche of the literature.

[Reply 1]: The authors thank for the reviewer’s comment and added the statement to emphasize the purpose and significance of this work.

[Changes]: Please see Lines 32~36 on Page 2, in the "Revision, changes marked".

[Comment 2]: The review is heavily skewed towards China. The authors must therefore state this clearly/ explicitly in their introduction or even title.

[Reply 2]: Thank you very much for your advice. The tittle of this work is modified accordingly.

[Changes]: Please see Lines 2 on Page 1, in the "Revision, changes marked".

[Comment 3]: Figures 4 and 5 are not properly cited. The citations MUST appear in their captions.

[Reply 3]: Thank you very much for your suggestion. The citations are added for both Figure 4 and Figure 5.

[Changes]: Please see Lines 1, and Line 3 on Page 3, in the "Revision, changes marked".

[Comment 4]: The prefatory statement (introductory or summary statement before bulleted points) is still missing.

[Reply 4]: The authors thank for the reviewer’s comment and added the summary before the bulleted points in conclusions.

Author Response File: Author Response.docx