Comprehensive Review of Smart Water Enhanced Oil Recovery Based on Patents and Articles

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

good revision

Comments on the Quality of English Language

good revision

Author Response

CHANGES MADE AND RESPONSES TO REVIEWERS' COMMENTS

REVIEWER 1

COMMENTS AND SUGGESTIONS FOR AUTHORS

1.1 - The English could be improved to more clearly express the research.

RESPONSE:

The authors thank the Reviewer. The text was improved, attending the suggestions of Reviewer 2 and Reviewer 3.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

Abstract

Energy matrix=energy mix?

It is a bit odd to state that EOR supports energy transition, considering that the general trend is to find fossil fuels environmentally unfriendly, therefore, enhancing fossil production is not so desirable in the context of energy transition... I suggest rephrasing this part of the first sentence in the abstract. Maybe something like this: „...has emerged as a promising strategy for reducing environmental impacts in the petroleum industry, producing a highly valuable energy source considering both its energy density and market value.“

„an article review of articles“ - ?

Line 19-20: „...assess themes, topics, and compositions of smart water EOR“ – this is a somewhat strange formulation. Maybe the authors meant „to analyze various aspects of using smart water for EOR, including its composition.“ ?

What is meant by „customized multivariate smart waters“ – please explain or rephrase in the abstract.

„reducing the need for new reservoirs“ - maybe replace with „alleviating the challenges of finding new reservoirs“

Introduction

Line 47 – what is meant by Pre Salt oil? Please elaborate in this paragraph (47-50) how/why this „Pre Salt oil“ is essential for achieving the stated goals.

Line 51 – it is pretty bold to say that EOR is potentially environmentally friendly, maybe rephrase to something like this: „EOR with smart water emerges as a potentially environmentally friendly option, as it uses cleaner fluid (smart water) and at the same time exploits the benefits of conventional EOR, which can increase recovery factor by 30-60%.“

Lines 54-55 just a comment (there's no real need for changing anything here but maybe you could elaborate it some more): there is a „catch“ with low oil prices – when oil price is low, users (expecially „big“ ones) are more keen to use oil „instead“ of renewables (although your statement is still relatively valid – when oil price is low, it is less economically viable to produce it which might incentivize investments in renewables)…

Lines 59-61 – this is the case only if chemicals are „spilled“ on or near the surface – when injected in deep isolated reservoirs (and when the process is conducted professionally, i.e., in accordance with all rules), there should be no risk of toxicity to aquatic and terrestrial ecosystems.

Materials and Methods

It seems that in line 179 some terms are in Spanish (in line 173 several languages were mentioned, but there are no terms in other languages in lines 176-180) – I believe this does not skew the research, but I find it curious

Results and discussion

Lines 243-244 this „noticeable decline“ doesn't seem so noticeable from the figure at first sight (I see there is a change in trend, but maybe it would be more obvious with a bit bigger figure?)…

Figure 2 – please unify the titles above the maps: instead of „C –„ write „(C)“

Maybe it could be of interest to analyze the trend of articles number per country (to see how interest in this topic changes over the years)

Line 565 – pharmaceutical products – did you explore the examples of pharmaceutical products that are mentioned in this context (it might be interesting to see which products were investigated in this regard, but it is not crucial)?

Author Response

CHANGES MADE AND RESPONSES TO REVIEWERS' COMMENTS

REVIEWER 2

COMMENTS AND SUGGESTIONS FOR AUTHORS

2.1 - The English is fine and does not require any improvement.

Abstract

2.2 - Energy matrix=energy mix?

RESPONSE:

The authors thank the Reviewer. The text has been corrected. It now reads (line15):

… energy mix …

2.3 - It is a bit odd to state that EOR supports energy transition, considering that the general trend is to find fossil fuels environmentally unfriendly, therefore, enhancing fossil production is not so desirable in the context of energy transition... I suggest rephrasing this part of the first sentence in the abstract. Maybe something like this: „...has emerged as a promising strategy for reducing environmental impacts in the petroleum industry, producing a highly valuable energy source considering both its energy density and market value.“

RESPONSE:

The authors thank the Reviewer. The text was improved according to the suggestion. It now reads (lines 15-18):

… has emerged as a promising strategy for reducing environmental impacts in the petroleum industry, producing a highly valuable energy source due to both its energy density and market value.

2.4 - „an article review of articles“ - ?

RESPONSE:

The authors thank the Reviewer. The text has been corrected. It now reads (line 20):

…and a review of articles…

2.5 - Line 19-20: „...assess themes, topics, and compositions of smart water EOR“ – this is a somewhat strange formulation. Maybe the authors meant „to analyze various aspects of using smart water for EOR, including its composition.“ ?

RESPONSE:

The authors thank the Reviewer. The text was improved according to the suggestion. It now reads (lines 20-21):

…to analyze various aspects of smart water for EOR, including its composition.

2.6 - What is meant by „customized multivariate smart waters“ – please explain or rephrase in the abstract.

RESPONSE:

The authors thank the Reviewer. The text was improved according to the suggestion. It now reads (lines 31-32):

…multivariated development of customized smart waters…

2.7 - „reducing the need for new reservoirs“ - maybe replace with „alleviating the challenges of finding new reservoirs“

RESPONSE:

The authors thank the Reviewer. The text was improved according to the suggestion. It now reads (lines 35-36):

… the efficient use of existing fields, alleviating the challenges of finding new reservoirs.

Introduction

2.8 - Line 47 – what is meant by Pre Salt oil? Please elaborate in this paragraph (47-50) how/why this „Pre Salt oil“ is essential for achieving the stated goals.

The authors thank the Reviewer. The text has been improved. It now reads (lines 49-58):

Pre-Salt production accounts for approximately 5% of global reserves and about 78% of Brazilian output [8–12] and will be essential for achieving the Sustainable Development Goas of Agenda 2023[13,14]. Its production process not only ensures high productivity but also contributes positively to the SDGs by reducing carbon dioxide emissions to nearly half the global average (SDGs 7, 13) and generating revenues al-located to social and environmental policies. The Social Fund directs resources to education and science (SDG 10), while its economic relevance strengthens strategies for climate adaptation and marine protection (SDG 14). In addition, it supports social programs (SDGs 1, 3, 4), fosters innovation (SDGs 8, 9), and reinforces the energy transition through lower emission intensity (SDGs 7, 13) [10,15,16]

The following references have been added:

8. de Mendonca, M.J.C.; Pereira Junior, A.O.; Pessanha, J.F.M.; Pereira, R.M.; Hunt, J.D. Measuring the Eco-nomic Impact of Pre-Salt Layer on the Productivity of the Oil and Natural Gas Sector. Resources 2025, 14, 32, doi:10.3390/resources14020032.
9. Petrobras S. A. Santos Basin Available online: https://petrobras.com.br/en/pre-sal?utm_source=chatgpt.com#2000m (accessed on 24 September 2025).
10. Pooler, M. Brazil Wants to Be a Climate Champion and an Oil Giant. Can It Be Both? Available online: https://www.ft.com/content/8d25d4d5-0258-4676-81ab-30bb711f4fd2?utm_source=chatgpt.com (accessed on 24 September 2025).
11. Branco, P.M. Petróleo Do Pré-Sal Available online: https://www.sgb.gov.br/petroleo-do-pre-sal?utm_source=chatgpt.com (accessed on 24 September 2025).
12. Vilardo, C.; Campos, A. Pre-Salt Oil and Its Contribution to Sustainable Development in Brazil: A Preliminary Assessment Available online: https://conferences.iaia.org/2011/pdf/presentations/IAIA11%20-%20Cristiano%20Vilardo%20-%20Pre-salt%20contribution%20to%20SD%20in%20Brazil.pdf?utm_source=chatgpt.com (accessed on 24 September 2025).
13. Petrobras, S.A. Relatório de Sustentabilidade 2024. 2024.

2.9 - Line 51 – it is pretty bold to say that EOR is potentially environmentally friendly, maybe rephrase to something like this: „EOR with smart water emerges as a potentially environmentally friendly option, as it uses cleaner fluid (smart water) and at the same time exploits the benefits of conventional EOR, which can increase recovery factor by 30-60%.“

RESPONSE:

The authors thank the Reviewer. The text was improved according to the suggestion. It now reads (lines 59-61):

… smart water emerges as a potentially environmentally friendly option, as it employs cleaner injection fluids while leveraging the benefits of conventional EOR, which can increase the recovery factor by 30–60% [17,18].

2.10 -  54-55 just a comment (there's no real need for changing anything here but maybe you could elaborate it some more): there is a „catch“ with low oil prices – when oil price is low, users (expecially „big“ ones) are more keen to use oil „instead“ of renewables (although your statement is still relatively valid – when oil price is low, it is less economically viable to produce it which might incentivize investments in renewables)…

RESPONSE:

The authors thank the reviewer. The text has been improved, taking into account the point raised by the reviewer. It now reads (lines 61-66):

Consequently, it contributes to reducing oil prices and, although influenced by multiple determinants, may stimulate the use of remaining revenues to finance the development of greener energy sources, such as solar photovoltaic deployment in the electricity mix [19].

2.11 -  59-61 – this is the case only if chemicals are „spilled“ on or near the surface – when injected in deep isolated reservoirs (and when the process is conducted professionally, i.e., in accordance with all rules), there should be no risk of toxicity to aquatic and terrestrial ecosystems.

RESPONSE:

The authors thank the reviewer. The text has been improved, taking into account the point raised by the reviewer. It now reads (line 70):

…which in the event of spills, …

Materials and Methods

2.12 - It seems that in line 179 some terms are in Spanish (in line 173 several languages were mentioned, but there are no terms in other languages in lines 176-180) – I believe this does not skew the research, but I find it curious

RESPONSE:

The authors thank the Reviewer. The text has been corrected. It now reads (lines 184-185):

…covering English, Portuguese, and Spanish.

Results and discussion

2.13 - Lines 243-244 this „noticeable decline“ doesn't seem so noticeable from the figure at first sight (I see there is a change in trend, but maybe it would be more obvious with a bit bigger figure?)…

RESPONSE:

The authors thank the Reviewer. The discussion has been corrected. It now reads (lines 249-252):

Another important aspect is the analysis of the impact of the COVID-19 pandemic years on annual trends. A decrease in the growth rate of EOR patents was observed (Figure 1A), consistent with previous findings by Quintella et al. [30]. The number of smart water EOR patents remains insufficient for reliable trend analysis.

2.14 - Figure 2 – please unify the titles above the maps: instead of „C –„ write „(C)“

RESPONSE:

The authors thank the Reviewer. The text has been corrected as suggested.

2.15 - Maybe it could be of interest to analyze the trend of articles number per country (to see how interest in this topic changes over the years)

RESPONSE:

The authors thank the reviewer. The discussion was improved by adding the suggested Figure 2D. A text with its analysis was inserted, which reads (lines 259-261):

Figure 2. World maps showing the countries of: (A) articles collaborative production; (B) first priority countries according to technology origin; (C) patent protection countries for technology potential markets; (D) annual evolution of accumulated articles for the top five countries.

2.16 - Line 565 – pharmaceutical products – did you explore the examples of pharmaceutical products that are mentioned in this context (it might be interesting to see which products were investigated in this regard, but it is not crucial)?

RESPONSE:

The authors thank the reviewer. The text has been revised. It now reads (lines 578-579):

…pharmaceutical-inspired procedures applied to EOR such as foam stability and nanofluidics,…

Author Response File: Author Response.pdf

Reviewer 3 Report

Comments and Suggestions for Authors

This manuscript provided insights into the research and development of smart water EOR technology throuh analyzing the published research papers and patents. This is an interesting work, but not recommended for publication in this fashion. Specific comments:

• It will help if the authors offer all the raw data as mentioned in the Materials and Methods section.
• It is recommended to explain the criteria applied to clean the data used for further analysis in the Results section.

• You may want to explain terms such as family size to make the manuscript easier to understand for readers from different backgrounds.

• As a review paper, it is in lack of fundamentals on the mechanisms of low salinity EOR which is important for the understanding of the Results section.
• The quality of some figures is poor. For instance, the font of Figure 6 is too small. 

Author Response

CHANGES MADE AND RESPONSES TO REVIEWERS' COMMENTS

REVIEWER 3

COMMENTS AND SUGGESTIONS FOR AUTHORS

3.1 - The English is fine and does not require any improvement.

This manuscript provided insights into the research and development of smart water EOR technology throuh analyzing the published research papers and patents. This is an interesting work, but not recommended for publication in this fashion. Specific comments:

3.2 - It will help if the authors offer all the raw data as mentioned in the Materials and Methods section.

RESPONSE:

The authors thank the Reviewer. The Data Availability Statement reads as follows (lines 738-740):

Most of the data used are available in the Supplementary Materials. Additional raw data sup-porting the conclusions of this article will be made available by the authors on request.

3.3 - It is recommended to explain the criteria applied to clean the data used for further analysis in the Results section.

RESPONSE:

The authors thank the reviewer. Both criteria applied to clean the data are now better explained, for articles as well as for patents. The revised texts read as follows:

(lines 175-177)

Data cleaning was performed by reading each patent individually, given their small number, and no exclusions were necessary.

(lines 194-200)

The data were exported to Excel, saved as a CSV file, and processed in RStudio version 2023.12.1 using Biblioshiny from the Bibliometrix package [40]. Key-word-based analyses were conducted following a cleaning process to merge similar terms and exclude irrelevant ones, ensuring that word clouds and keyword co-occurrences were not affected. For this purpose, 5,969 keywords were evaluated individually; 495 redundant keywords, which merely repeated terms from the search scope, were removed, and 1,056 keywords were standardized. After these procedures, a total of 1,395 smart water articles remained.

A new reference was added:

40. Bibliometrix Biblioshiny Available online: https://www.bibliometrix.org/home/index.php/layout/biblioshiny (accessed on 28 August 2025).

3.4 - You may want to explain terms such as family size to make the manuscript easier to understand for readers from different backgrounds.

RESPONSE:

The sentence in the methodology section was restructured to facilitate readers’ understanding. It now reads (lines 154-155):

To avoid duplicate results due to filings with the same technical content across multiple countries, patent families were considered based on the FAMPAT criterion [37] and will henceforth be referred to simply as "patents."

The following reference was maintained to allow readers to further explore the subject in depth:

37. Questel Orbit. The Fampat Collection Available online: https://intelligence.help.questel.com/en/support/solutions/articles/77000436698-fampat-family-construction-rules (accessed on 5 August 2025).

3.5 - As a review paper, it is in lack of fundamentals on the mechanisms of low salinity EOR which is important for the understanding of the Results section.

RESPONSE:

The authors thank the reviewer. Several studies already demonstrate that, although many mechanisms have been proposed, it is still not clear how they interact with each other. In fact, there are conflicting experimental results and field applications. This aspect is highlighted in various parts of the text. In addition, recent references that explore these mechanisms comprehensively have been included, for example:

45. RezaeiDoust, A.; Puntervold, T.; Austad, T. Chemical Verification of the EOR Mechanism by Using Low Saline/Smart Water in Sandstone. Energy & Fuels 2011, 25, 2151–2162, doi:10.1021/ef200215y.
46. Austad, T.; Shariatpanahi, S.F.; Strand, S.; Aksulu, H.; Puntervold, T. Low Salinity EOR Effects in Limestone Reservoir Cores Containing Anhydrite: A Discussion of the Chemical Mechanism. Energy & Fuels 2015, 29, 6903–6911, doi:10.1021/acs.energyfuels.5b01099.
47. Behera, U.S.; Sangwai, J.S.; Baskaran, D.; Byun, H.-S. A Comprehensive Review on Low Salinity Water Injection for Enhanced Oil Recovery: Fundamental Insights, Laboratory and Field Studies, and Economic As-pects. Energy & Fuels 2025, 39, 72–103, doi:10.1021/acs.energyfuels.4c04562.
48. Lyu, C.; Zhong, L.; Ning, Z.; Chen, M.; Cole, D.R. Review on Underlying Mechanisms of Low Salinity Wa-terflooding: Comparisons between Sandstone and Carbonate. Energy & Fuels 2022, 36, 2407–2423, doi:10.1021/acs.energyfuels.1c04248.
49. Mumbere, W.; Sagala, F.; Gupta, U.; Bbosa, D. Reservoir Potential Unlocked: Synergies Between Low-Salinity Water Flooding, Nanoparticles and Surfactants in Enhanced Oil Recovery─A Review. ACS Omega 2025, 10, 31216–31261, doi:10.1021/acsomega.5c02533.
50. Liu, D.; Xu, J.; Zhao, H.; Zhang, X.; Zhou, H.; Wu, D.; Liu, Y.; Yu, P.; Xu, Z.; Kang, W.; et al. Nanoemulsions Stabilized by Anionic and Non-Ionic Surfactants for Enhanced Oil Recovery in Ultra-Low Permeability Reservoirs: Performance Evaluation and Mechanism Study. Colloids Surf A Physicochem Eng Asp 2022, 637, 128235, doi:10.1016/j.colsurfa.2021.128235.
51. Zhao, M.; Cheng, Y.; Wu, Y.; Dai, C.; Gao, M.; Yan, R.; Guo, X. Enhanced Oil Recovery Mechanism by Surfactant-Silica Nanoparticles Imbibition in Ultra-Low Permeability Reservoirs. J Mol Liq 2022, 348, 118010, doi:10.1016/j.molliq.2021.118010.

106 - Sohal, M.A.; Thyne, G.; Søgaard, E.G. Review of Recovery Mechanisms of Ionically Modified Waterflood in Carbonate Reservoirs. Energy & Fuels 2016, 30, 1904–1914, doi:10.1021/acs.energyfuels.5b02749.

132. Da, Q.; Yao, C.; Zhang, X.; Li, L.; Lei, G. Investigation on Flow Resistance Reduction and EOR Mechanisms by Activated Silica Nanofluids: Merging Microfluidic Experimental and CFD Modeling Approaches. J Mol Liq 2022, 368, 120646, doi:10.1016/j.molliq.2022.120646.
133. Liang, T.; Wang, H.; Yang, C. Mechanisms and Effects of Amphiphilic Lamellar Nanofluid for Enhanced Oil Recovery in Low Permeability Reservoirs. J Mol Liq 2024, 397, 124043, doi:10.1016/j.molliq.2024.124043.

142 .              Wang, Z.; Lin, X.; Yu, T.; Zhou, N.; Zhong, H.; Zhu, J. Formation and Rupture Mechanisms of Vis-co-Elastic Interfacial Films in Polymer-Stabilized Emulsions. J Dispers Sci Technol 2019, 40, 612–626, doi:10.1080/01932691.2018.1478303

153. Namaee-Ghasemi, A.; Behbahani, H.S.; Kord, S.; Sharifi, A. Geochemical Simulation of Wettability Alteration and Effluent Ionic Analysis during Smart Water Flooding in Carbonate Rocks: Insights into the Mechanisms and Their Contributions. J Mol Liq 2021, 326, 114854, doi:10.1016/j.molliq.2020.114854

3.6 - The quality of some figures is poor. For instance, the font of Figure 6 is too small.

RESPONSE:

The authors thank the reviewer. The details of Figure 6 are expanded in Figures 7, 8, 9, and 10. The caption of Figure 6 was corrected. It now reads (lines 394-395):

Figure 6. Co-occurrence network of keywords plus for smart water EOR articles. Details of each cluster are presented in Figures 7–10.

Author Response File: Author Response.pdf

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The authors have corrected the manuscript, and I find it acceptable for publication.