An Ultra-Stable Polysaccharide Gel Plugging Agent for Water Shutoff in Mature Oil Reservoirs
Round 1
Reviewer 1 Report
Comments and Suggestions for AuthorsThis manuscript develops a chitosan-based (CTS/MBA) gel system designed to improve water shutoff in high-temperature, high-shear oil reservoir conditions, demonstrating enhanced thermal stability, salt tolerance, and mechanical strength compared to traditional polyacrylamide gels, and their laboratory tests reveal the gel’s optimized performance, suggesting its potential for effective application in mature oilfields. Overall organization and style of writing of this manuscript are good enough to be published. The authors are cordially encouraged to carry out a minor revision for publication of the manuscript in this journal, in response to the questions and comments below.
1. It would improve the manuscript to briefly outline the limitations of previous water shutoff methods and highlight the unique attributes of the CTS/MBA gel in addressing these challenges.
2. Could the authors consider adding a flowchart of the experimental protocols? This would help enhance readers’ understanding of the study’s methodology.
3. Please include a more detailed comparison with existing water shutoff gels, such as polyacrylamide and other biopolymer gels, to clearly contextualize the advantages of the CTS/MBA gel system.
4. The Michael addition reaction mechanism is referenced as a key process in gelation, but there is limited information provided in the manuscript. Could the authors add a paragraph explaining this mechanism, along with relevant references, in the introduction? Additionally, expanding on the Michael addition reaction’s role in enhancing stability and providing a molecular-level explanation of how CTS/MBA composition influences thermal and shear resistance would strengthen the rationale for this system’s superiority.
5. Since all results in this manuscript are based on experimental observations, adding error bars in the figures would improve the reliability of the data. Additionally, please ensure all figures have appropriate legends, labels, and practical benchmarks for comparison, as this would further highlight the gel’s performance benefits.
6. Check out the format of references (eg. 6, 18,24, 35, 36).
Author Response
Please see the attachment.
Author Response File: 
Author Response.pdf
Reviewer 2 Report
Comments and Suggestions for Authors
The following points should be addressed before publication:
- The manuscript should be prepared using a property of the Microsoft Word template or LaTeX template for the Applied Sciences journal.
- Sufficient details of used materials and techniques should be described to allow others to replicate and build on published results, i.e., The lack of specification for commercial samples of chitosan - molecular weight
- On page 6, lines 19-20, the authors wrote, "The viscosity was measured through a Brookfield DV-III viscometer at 7.34 s-1.” What was the temperature during measurement? What measuring system was used, i.e. cone-plate or other?
- How many samples of one type (or the number of experiment replicates) were used in the studies? Lack of information about the number of replicates of the experiment.
- Statistical analysis should be emphasised to support the results, discussion and conclusion. Please correct.
- How is the reproducibility of the used procedures? Repeating the preparation experiments and characterising and evaluating the results should prove this.
- Please check the text: Some typing/format errors were found.
Comments on the Quality of English LanguagePlease check the text: Some typing/format errors were found.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Reviewer 3 Report
Comments and Suggestions for AuthorsOverall Evaluation
The manuscript discusses developing and analyzing chitosan (CTS)-based gel plugging agent cross-linked with N, Methylene Bisacrylamide (MBA). The approach seeks to address the challenges of excessive water production in mature oilfields. The study is methodical and includes characterization and analysis of thermal and mechanical stability under harsh reservoir conditions, and it is relevant to the field of petroleum engineering. However, some areas require further clarification, refinement, and strengthening to enhance the manuscript's impact and readability.
Major Comments:
1. Introduction: While the study claims novelty, using chitosan and MBA in gel systems has been explored in other contexts. The manuscript should explicitly highlight how this work differs from existing studies regarding formulation, testing methods, or reservoir applications. (See ref: Geoenergy Science and Engineering (2013), 230, 212136). Please also include all relevant citations regarding prior works (E.g. page 11, line 2)
2. The manuscript discusses rapid gelation with increasing MBA and CTS concentration but does not provide quantitative details. How do these times compare to existing polymer gel systems? A plateau in gelation time is observed at a specific concentration, explain this observation and support it mechanistically.
3. Include Michael's addition mechanism for gelation and describe the chemical structures at the beginning of the manuscript.
4. For different gel compositions, more comprehensive rheological analyses, such as Young’s modulus and swelling ratios, should also be discussed. Relate this to the observed improvements in gel properties.
5. The SEM images indicate a three-dimensional microstructure, but there is no quantitative analysis of pore size, network density, or morphology.
6. The use of chitosan suggests potential environmental advantages over synthetic polymers, but this aspect is not addressed. Discussing biodegradability or environmental compatibility could strengthen the manuscript's impact.
7. How does the system perform in actual reservoir conditions? 1 ) Are there limitations in scalability or injection feasibility? 2) How does the proposed system compare to conventional gels in field trials?
Minor Comments:
1. Consider consolidating the discussion of experimental evaluations and findings for conciseness.
2. Ensure that all figures are adequately labeled. Use different markers (plot symbols) in the graphs in Figure 1-4.
3. Define key terms like “gel strength”, and "thermal aging" more precisely. Describe the method and cite appropriate references for testing conditions.
4. Outline directions for future research. Discussing potential scalability, alternative cross-linkers, and limitations of the system described.
5. Improve the experimental section by including details of methods and procedures used for synthesis and characterization.
6. Include additional figures or discussion in SI and improve the presentation of results.
Comments on the Quality of English LanguageThe English language in the manuscript is generally acceptable for publication, but it would benefit from minor revisions to eliminate redundancy, improve sentence structure, and enhance clarity. These improvements will make the manuscript more comprehensible and concise.
Author Response
Please see the attachment.
Author Response File: Author Response.pdf
Round 2
Reviewer 2 Report
Comments and Suggestions for AuthorsThe authors have corrected and modified their manuscript. I recommend the article for publication.
Reviewer 3 Report
Comments and Suggestions for AuthorsAll the comments and questions were addressed carefully and appropriately in the revised manuscript.
