Study on the Mechanism of Fiber Fracturing Fluid Controlling Pulverized Coal Transportation

Round 1

Reviewer 1 Report

A brief summary

China's coalbed methane resources are abundant, but most of the reservoirs have the “three low” features. It is necessary to carry out hydraulic fracturing and other measures to increase the output of single well. Currently, active water is mostly used in the coal seams, but the active water has problems such as weak proppant-carrying capacity, strong filtration loss, and high sand -plugging risk, while the fiber-based  fracturing fluid precisely compensates for these disadvantages.

The article is dedicated to an actual and important issue - Fiber fracturing fluid technology for pulverized coal treatment but it has many shortcomings and needs to be improved.

Specific comments:

1. Abbreviations (CBM, CFD, KTL) should be explained when first used in the text.
2. Citation of references in the text should be according to the instructions (e.g. Bai et al. (2015, 2017,2017) If two papers are in the same year they should be marked differently e.g. 2017a and 2017b.
3. There are a lot of mistakes in the text related to: space, uppercase or lowercase letter, missing dot at the end of the sentence, the title of the figures and similar things that need to be corrected.
4. Fig 1.: In the text, explain to which concentration and type of fiber the microstructure shown refers.
5. 2. and Fig 4: The text in the figure is illegible or in Chinese. That needs to be corrected.
6. Below formulas (6) and (7) are explained parameters that are not included in them, eg “a” and “M”, and there is no explanation for “x₁”.
7. Explain all those labels that are not explained in the text and are found in formulas (10), (11) and (15)).
8. I suggest that at the end of the paper you add a list of symbols used in formulas with names and units.
9. Table 1. The name of the table is written above, not below the table.
10. In Table 1 is written, for series A in the Flow rate/Closure pressure column, 200 ml/min. However, Figures 7 and 8 show for Series A the dependence of Production of coal fine and Conductivity on closure pressure and not on flow rate.
11. In Table 1 is written, for series B in the Flow rate/Closure pressure column, 5MPa. However, Figures 9 and 10 show for Series B the dependence of Production of coal fine and Conductivity on flow rate and not on closure pressure.
12. The results shown in 11 Coal powder particle size distribution under closure pressure 5MPa and flow rate 100ml/min should be commented on in the text.
13. Why are the marks B-1 to B-5 written in Figures 11, 12 and 13 when this fluid is of the same composition as A-1 to A-5?
14. Lines 218-222: The sentence „The particle size analysis of pulverized coal produced at a flow rate 200 or 300 ml/min and closure pressure 5 MPa is performed using a laser particle size analyzer Mastersizer2000. Figure 11 shows that when the flow rate is 200 mL/min, the pulverized coal particle size distribution curve takes the form of a bimodal right polar peak, and the particle size value N varies from 1 to 464 μm.“ is not correct because the measurements were carried out at 1 a flow rate 100, 200 or 300 ml/min and closure  pressure 5 MPa, and the comment refers to Fig. 12, which is incorrectly marked as Fig.22.
15. Conclusions should be better written with more data resulting from the research.
16. Prior to the conclusion, shortcomings or limitations of the conducted research and recommendations for further research should be added.
17. References should be written according to the instructions, pay attention to the way the author's name is written.

Author Response

Manuscript Number: energies-1565239

Title: Study on the Mechanism of Fiber Fracturing Fluid Controlling Pulverized Coal Transportation

Dear Editor and Reviewers,

Thank you for your comments on our manuscript entitled “Study on the Mechanism of Fiber Fracturing Fluid Controlling Pulverized Coal Transportation” (Manuscript Number: energies-1565239). These comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied the comments carefully and have made corrections, which we hope to meet with approval. Revised portions are marked in red in the manuscript. The main corrections in the paper and the responses to the reviewers’ comments are as follows.

Looking forward to hearing from you.

Sincerely yours,

Haifeng Zhao

Reviewer #1:

1. Abbreviations (CBM, CFD, KTL) should be explained when first used in the text.

Thanks for your comments and suggestions on the " Abbreviations " of the article, the Abbreviations in the article have been carefully revised. For your convenience, changed parts have been marked in red.

CBM (Coalbed Methane)

CFD (Computational Fluid Dynamics)

KTL is the company's product model

2. Citation of references in the text should be according to the instructions (e.g. Bai et al. (2015, 2017,2017) If two papers are in the same year they should be marked differently e.g. 2017a and 2017b.

Thanks for your comments and suggestions on the " Citation of references " of the article, it have been carefully revised. For your convenience, changed parts have been marked in red.

3. There are a lot of mistakes in the text related to: space, uppercase or lowercase letter, missing dot at the end of the sentence, the title of the figures and similar things that need to be corrected.

Thank you for pointing this out. It has been corrected.

4. Fig 1.: In the text, explain to which concentration and type of fiber the microstructure shown refers.

Thanks for your comments, Fig 1. in the article have been carefully revised.

5. Fig 2. and Fig 4: The text in the figure is illegible or in Chinese. That needs to be corrected.

Thank you for pointing this out. It has been corrected.

6. Below formulas (6) and (7) are explained parameters that are not included in them, eg "a"and "M", and there is no explanation for "x".

Thanks for pointing this out and the parameters in the article have been carefully revised. For your convenience, changed parts have been marked in red.

7. Explain all those labels that are not explained in the text and are found in formulas (10), (11) and (15))

Thanks for your comments and the parameters in the article have been carefully revised. For your convenience, changed parts have been marked in red.

8. I suggest that at the end of the paper you add a list of symbols used in formulas with names and units

Thank you for your comments and suggestions.

9. Table 1. The name of the table is written above, not below the table.

Thanks for pointing this out. It has been corrected.

10. In Table 1 is written, for series A in the Flow rate/Closure pressure column, 200 ml/min. However, Figures 7 and 8 show for Series A the dependence of Production of coal fine and Conductivity on closure pressure and not on flow rate.

Thanks for your comments. FIG. 7 and 8 respectively study the effects of different proppant and fiber components on pulverized coal production and coal permeability, so Flow rate and Closure pressure are taken as separate influencing factors. For example, in the study of Flow rate, the influence of Closure pressure is not considered, that is, only the change of coal powder quantity and permeability under single factor condition is studied, instead of the change of Flow rate and Closure pressure coupling condition.

11. In Table 1 is written, for series B in the Flow rate/Closure pressure column, 5MPa. However, Figures 9 and 10 show for Series B the dependence of Production of coal fine and Conductivity on flow rate and not on closure pressure.

Thanks for your comments. FIG. 9 and 10 respectively study the effects of different proppant and fiber components on pulverized coal production and coal permeability, so Flow rate and Closure pressure are taken as separate influencing factors. For example, in the study of Flow rate, the influence of Closure pressure is not considered, that is, only the change of coal powder quantity and permeability under single factor condition is studied, instead of the change of Flow rate and Closure pressure coupling condition.

12. The results shown in 11 Coal powder particle size distribution under closure pressure 5MPa and flow rate 100ml/min should be commented on in the text.

Thanks for your comments and suggestions, changed parts have been marked in red.

13. Why are the marks B-1 to B-5 written in Figures 11, 12 and 13 when this fluid is of the same composition as A-1 to A-5?

Thank you for your comments and its components are the same, but the influencing factors are different.

14. Lines 218-222: The sentence , The particle size analysis of pulverized coal produced at a flow rate 200 or 300 ml/min and closure pressure 5 MPa is performed using a laser particle size analyzer Mastersizer2000. Figure 11 shows that when the flow rate is 200 mL/min, the pulverized coal particle size distribution curve takes the form of a bimodal right polar peak, and the particle size value N varies from 1 to 464 um." is not correct because the measurements were carried out at 1 a flow rate 100, 200 or 300 ml/min and closure pressure 5 MPa, and the comment refers to Fig. 12, which is incorrectly marked as Fig.22.

Thank you for your comments, the wording and Fig. in the article have been carefully revised. For your convenience, changed parts have been marked in red.

15. Conclusions should be better written with more data resulting from the research.

Thanks for your comments and suggestions on the "Conclusions " of the article, for your convenience, changed parts have been marked in red.

By analyzing the particle size distribution of coal seam produced at different flow rates, it is found that when the flow rate is 100mL/min, the distribution curve of coal particle size is in the form of double peak right pole peak, and the particle size value varies from 1 to 337µm. At 200ml/ min and 300ml/ min, the particle size ranges from 1 to 464µm and from 1 to 1015µm. Therefore, the larger the flow rate, the wider the particle size distribution and the larger the particle size.

16. Prior to the conclusion, shortcomings or limitations of the conducted research and recommendations for further research should be added

Thanks for your comments. Based on your ideas, we have made targeted modifications to Prospect prior to the conclusion.

Based on the properties of coal and rock, this paper studies the properties of fiber fracturing fluid and the influence of degradable fiber on pulverized coal transport from the aspects of compatibility between fiber and proppant, static sand suspension experiment and reservoir damage, and analyzes the mechanical action mechanism of fiber on pulverized coal. However, without extensive field application, the practical significance of fiber fracturing fluid has not been fully demonstrated. Therefore, the author will actively contact relevant oil, gas and coal fields and adopt the fracturing fluid developed in this paper to test its practical effect in actual fracturing engineering.

17. References should be written according to the instructions, pay attention to the way the author's name is written.

Thank you for your comments and suggestions on the " References " of the article, the author's name in the article have been carefully revised.

Author Response File: Author Response.pdf

Reviewer 2 Report

In principle, the presented scientific work seems solid. Besides the minor comments in the attached pdf, there are a few major issues that need to be addressed:

• Language and especially formatting needs to be improved THROUGHOUT THE MANUSCRIPT! The placement of spaces and punctuation in general is sloppy.
• The technical figure quality (graphical resolution) is poor and needs to be improved.
• The authors need to improve the explanation of their work for a wider audience. The paper relies on many specialized abbreviations and terms, which require explanation. Also, uncommon units (e.g. for hydraulic conductivity) should be explained or transferred in more common standard units.

Besides that and the minor comments in the pdf, I believe the work is suitable for publication in Energies.

Comments for author File: Comments.pdf

Author Response

Manuscript Number: energies-1565239

Title: Study on the Mechanism of Fiber Fracturing Fluid Controlling Pulverized Coal Transportation

Dear Editor and Reviewer2,

Thank you for your comments on our manuscript entitled “Study on the Mechanism of Fiber Fracturing Fluid Controlling Pulverized Coal Transportation” (Manuscript Number: energies-1565239). These comments are all valuable and very helpful for revising and improving our paper, as well as the important guiding significance to our researches. We have studied the comments carefully and have made corrections, which we hope to meet with approval. Revised portions are marked in red in the manuscript. The main corrections in the paper and the responses to the reviewers’ comments are as follows.

Looking forward to hearing from you.

Sincerely yours,

Haifeng Zhao

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

The authors accepted the remarks and thus significantly improved their paper