Fuzzy-Ball Fluids: Fundamentals, Mechanisms, and Prospects for Clean Energy and Oilfield Applications

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The article presents a detailed study of a new class of chemical fluids known as "fuzzy-ball fluids". The authors analyze their fundamental properties, mechanisms of action, and prospects for use in conventional oil and gas technologies and in the field of clean energy. The main emphasis is on the ability of these fluids to adapt to complex geological conditions and their potential applications in areas such as enhanced oil recovery (EOR), hydraulic fracturing, hydrogen storage, carbon capture, and geothermal energy. In particular, the authors note: "The fuzzy-ball fluid is characterized by its viscoelastic behavior, with low viscosity at high shear rates, allowing it to be easily injected into reservoirs and maintaining stability in challenging environments." (p. 3). This indicates a significant potential for the technology to improve the efficiency of oil recovery. In addition, I would like to note that the article considers the selective properties of the fluid, allowing it to direct flows into zones with different permeabilities. For example, "Fuzzy-ball fluids exhibit a lower plastic viscosity compared to oil-based and polymer-based fluids, which enhances their injectability in low-permeability zones." (p. 5). However, despite all the advantages, the authors honestly point out the existing problems and limitations of this technology. In the section on challenges and prospects, it is emphasized that "Despite its promise, the broader adoption of fuzzy-ball fluids faces critical challenges, including ensuring material stability under extreme and complex subsurface conditions, improving economic feasibility compared to traditional methods, and addressing environmental concerns related to fluid components." (p. 12). This aspect raises an important question about the need for further research aimed at stabilizing the composition of the fluid and its long-term efficiency. In general, I liked the article and it does not raise any fundamental comments. I would like to note only a number of shortcomings in the work.
1. "sealapluging" → the correct version is "seal-plugging" (p. 1, abstract). 2. "reservoir and control lost circulation" → should be "reservoir and control lost circulation" (p. 2, introduction, extra space).
3. "fluids exhibit a lower plastic viscosity compared to oil-based and polymer-based fluids, which enhances their injectability in low-permeability zones." — here it should be clarified that low viscosity improves injectability into low-permeability zones, but this is not always an advantage.
4. "caprocks is critical for preventing the migration of CO2 out of the storage site" → more correctly "caprocks are critical", since "caprocks" is plural (p. 12).
5. Some sentences are too long and difficult to understand. For example,:
"Despite its promise, the…………." — It is better to break this into several sentences for readability.
6. There are unnecessary repetitions of terms, for example, "self-adapting and plugging mechanisms" is repeated too often in one section.
7. There are double spaces in some places.
8. There is a lack of consistency in the use of upper and lower case letters in the headings.
9. Line 34. The text "and control lost circulation [2]". I recommend adding doi.org/10.3390/en18041012

Comments on the Quality of English Language

I recommend that you read the work of a native speaker.

Author Response

Comments 1: "sealapluging" → the correct version is "seal-plugging" (p. 1, abstract).

Response 1: Thank you for your careful review and suggestions. Based on your comments, we identified an error in the spelling of sealaplugging and have corrected it accordingly. Additionally, we would like to clarify that sealaplugging is a newly developed technical term by Professor Zheng Lihui, specifically coined to capture the unique plugging functionality of fuzzy-ball fluids and other similar fluids. This term serves as a trademark concept of our research group to define the distinct characteristics of these fluids and similar future developments. Recently published articles have utilized this term. Therefore, the authors decided that the term “sealaplugging” be retained.

Comments 2: "reservoir and control lost circulation" → should be "reservoir and control lost circulation" (p. 2, introduction, extra space).

Response 2: Thank you for your suggestions. We have corrected the extra space in the introduction as recommended.

Comments 3: "fluids exhibit a lower plastic viscosity compared to oil-based and polymer-based fluids, which enhances their injectability in low-permeability zones." — here it should be clarified that low viscosity improves injectability into low-permeability zones, but this is not always an advantage.

Response 3: Thank you for your valuable feedback. We have clarified that while lower viscosity improves injectability in low-permeability zones, it may also present challenges such as increased fluid loss or reduced control over placement. This consideration has been incorporated into the revised text to provide a more balanced discussion. The revised statement is shown below:

Fuzzy-ball fluids exhibit a lower plastic viscosity compared to oil-based and poly-mer-based fluids, which enhances their injectability in low-permeability zones. However, while lower viscosity facilitates injection, it may also lead to increased fluid loss or reduced control over placement in certain reservoir conditions, which should be carefully considered in field applications.

Comments 4: "caprocks is critical for preventing the migration of CO2 out of the storage site" → more correctly "caprocks are critical", since "caprocks" is plural (p. 12).

Response 4: Thank you for pointing out this issue. We have modified the sentence accordingly.

Comments 5: Some sentences are too long and difficult to understand. For example, "Despite its promise, the…………." — It is better to break this into several sentences for readability.

Response 5: Thank you for your suggestion. We have revised the sentence by breaking it into smaller parts to improve readability while maintaining clarity. We also modified similar cases throughout the manuscript.

Comments 6: There are unnecessary repetitions of terms, for example, "self-adapting and plugging mechanisms" is repeated too often in one section.

Response 6: Thank you for your observation. We have modified accordingly.

Comments 7: There are double spaces in some places.

Response 7: We have checked and removed all double spaces. Thank you.

Comments 8: There is a lack of consistency in the use of upper and lower case letters in the headings.

Response 8: Thank you for your valuable feedback. The corrections have been implemented.

Comments 9: Line 34. The text "and control lost circulation [2]". I recommend adding doi.org/10.3390/en18041012.

Response 9: Thank you for your suggestions. We have added this paper into the reference list as suggested “Ilyushin, Y.; Nosova, V.; Krauze, A. Application of Systems Analysis Methods to Construct a Virtual Model of the Field. Energies 2025, 18, 1012. https://doi.org/10.3390/en18041012.

Author Response File: Author Response.docx

Reviewer 2 Report

Comments and Suggestions for Authors

The paper does a great job explaining the properties and mechanisms of fuzzy-ball fluids, but it would be helpful to include a direct comparison with other existing sealing and plugging technologies. How do they perform relative to polymer-based fluids or nanoparticles in similar applications? Also, the discussion of challenges is valuable, but it could be expanded to include specific areas where further research is needed. 

The section on self-adapting properties is interesting, but the mechanics of how these fluids respond to varying downhole conditions could be explained more clearly. A schematic or simple flow diagram illustrating their behavior under pressure and temperature changes would make this easier to understand. 

Some terms, such as "intelligent sealing" and "self-healing," are used without a precise definition. Clarifying these terms and ensuring consistency in their usage throughout the paper would make the discussion more precise

Author Response

Comments 1: The paper does a great job explaining the properties and mechanisms of fuzzy-ball fluids, but it would be helpful to include a direct comparison with other existing sealing and plugging technologies. How do they perform relative to polymer-based fluids or nanoparticles in similar applications? Also, the discussion of challenges is valuable, but it could be expanded to include specific areas where further research is needed.

Response 1: Thank you for your insightful comments. A direct comparison of fuzzy-ball fluids with polymer-based and other conventional sealing and plugging fluids has been provided in Chapter 2 and further elaborated in Chapter 2.2 of the revised manuscript. These sections highlight the advantages of fuzzy-ball fluids in terms of adaptability, plugging efficiency, and rheological properties related to other systems. Additionally, specific areas where further research is needed have been discussed in detail in Chapter 4.3 and reinforced in the conclusion and recommendation section. We appreciate your feedback and believe these discussions address your concerns.

Comments 2: The section on self-adapting properties is interesting, but the mechanics of how these fluids respond to varying downhole conditions could be explained more clearly. A schematic or simple flow diagram illustrating their behavior under pressure and temperature changes would make this easier to understand.

Response 2: Thank you for your valuable suggestion. We have clarified the mechanics of how fuzzy-ball fluids respond to varying downhole conditions in the revised manuscript. Additionally, we included a schematic to visually illustrate their behavior under pressure and temperature changes, enhancing clarity for readers. Here is the revised section:

2.3.1. Self-adapting mechanisms

The adapting nature of fuzzy-ball fluids is largely attributed to its ball-like structures, which consist of high-strength, gas-filled bubbles capable of deforming to diverse flow channel geometries. This deformation adaptation mechanism allows the fluids to penetrate pores, fractures, and seepage channels of varying sizes, ensuring retention and efficient plugging even in highly heterogeneous formations, shown in Figure 2.

 

Figure 2. Schematic representation of the self-adapting mechanism of fuzzy-ball fluids under varying downhole conditions.

As can be seen from Figure 2 that the self-adaptive mechanism of fuzzy-ball fluid exhibits unique behaviors under varying temperature and pressure conditions.

In the wellbore, where temperatures are relatively low and pressures are high, the micro-bubbles of the fuzzy-ball fluid slightly contract at low temperatures, facilitating fluid flow, while being compressed under high pressure to maintain structural integrity and ensure stable transportation.

At the bottomhole, where high temperature and high pressure coexist, the size of the micro-bubbles in the fuzzy-ball fluid reaches a dynamic balance under the influence of these two forces. High temperature tends to cause the bubbles to expand, while high pressure tends to compress them. Ultimately, the volume of the bubbles adjusts to an intermediate state based on the specific temperature and pressure conditions. High temperature causes the bubbles to thermally expand, increasing their volume and enhancing their ability to plug larger pores, while extremely high pressure compresses the bubbles, allowing them to pass through tight pore spaces.

In the formation, where temperature variations are significant, the fuzzy-ball fluid expands in high-temperature zones to enhance plugging and contracts in low-temperature zones to penetrate deeper into narrow channels. Simultaneously, due to the uneven pressure distribution in the formation, the bubbles are compressed in high-pressure regions to pass through dense pores and expand in low-pressure regions to improve plugging efficiency. At the front end, where the pressure is low, the bubbles gradually increase in size, raising flow resistance. Additionally, irregular underground leakage channels further increase flow resistance until the pressure of the working fluids equals the formation pressure. At this point, the bubbles stop flowing within the leakage channels, effectively halting further leakage. Subsequent bubbles also cease flowing and, together with the front-end bubbles, accumulate into a conical shape. Meanwhile, owning to the high formation temperature, heat exchange occurs with the bubbles, causing them to expand further and strengthen their plugging capability.

Moreover, chemical interactions between the fluid's polymers and surfactants and the rock minerals play a complementary role. These interactions involve adsorption and bonding processes that enhance the mechanical properties of the reservoir rock, including its tensile and shear strength, while reducing collapse stress and increasing leakage pressure. Such interactions also contribute to dynamic adaptation by reinforcing the plugging structures, ensuring long-term stability under fluctuating reservoir conditions. By integrating chemical and mechanical synergies, the performance of fuzzy-ball fluids can be optimized under various operational parameters.

 

Comments 3: Some terms, such as "intelligent sealing" and "self-healing," are used without a precise definition. Clarifying these terms and ensuring consistency in their usage throughout the paper would make the discussion more precise.

Response 3: We have modified accordingly. We appreciate the reviewers’ comments/suggestions and we believe these revisions will enhance the manuscript’s readability and precision. Thank you again for your feedback.

Author Response File: Author Response.docx