Review Reports

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

The manuscript presents an extensive study of nanoparticle–surfactant composite systems for enhanced oil recovery, with special focus on SiO₂ nanoparticles combined with a nonionic surfactant. The topic is relevant to the scope of Nanomaterials, particularly regarding interfacial phenomena, colloidal stability, and functional nanomaterials in applied systems. The work is experimentally rich and addresses an important applied problem. However, the paper is too long, sometimes overly descriptive, and lacks critical discussion in several key physicochemical aspects. Some interpretations are presented as established facts without sufficient theoretical or literature support. Therefore, a substantial revision of the manuscript should be done before acceptance.

-The manuscript does not clearly position its novelty relative to existing literature. Authors should state what is new compared to previous nanoparticle–surfactant EOR studies, and clarify whether the main contribution is methodological, mechanistic, or performance-based

-The “wedging effect” and structural disjoining pressure are mentioned repeatedly, but quantitative validation under real porous media conditions is limited.

-The role of surface charge, surfactant adsorption isotherms, and competitive adsorption between surfactant, nanoparticles, and crude oil components is not sufficiently discussed.

-The interaction between OP-10 and SiO₂ is attributed mainly to steric stabilization, but hydrogen bonding and specific adsorption should also be considered.

-Distinguishing clearly between experimental observation and conceptual illustration

-Reducing speculative statements or supporting them with references

-Experimental conditions in rheological experiments should be clearly stated

-The link between interfacial viscoelasticity and actual oil displacement performance should be discussed more critically.

-The reported emulsion droplet sizes (5–15 μm) are relatively large for pore-scale transport in low-permeability rocks.

-The manuscript contains repetitive explanations of known EOR mechanisms

-Grammar and spelling should be carefully revised

-Several equations (e.g., disjoining pressure, adsorption energy) are presented without clear assumptions or units consistency.

-Ensure consistent citation style

-Abbreviations should be defined at first us

Author Response

Comment 1: The manuscript does not clearly position its novelty relative to existing literature.

Response 1: We have substantially revised the Introduction section to clearly articulate our novel contributions. Specifically, we have added a new paragraph (marked in bold in the revised manuscript) that explicitly states: "(1) the quantitative relationship between nanoparticle-surfactant ratio and synergistic performance in low-permeability cores with permeability below 1 mD; (2) the contribution of hydrogen bonding and specific adsorption mechanisms in OP-10/SiO₂ interactions beyond simple steric stabilization; (3) the role of mineral-nanoparticle and mineral-surfactant interactions in determining wettability alteration efficiency; and (4) the competitive adsorption dynamics between surfactant molecules, nanoparticles, and crude oil components."

Comment 2: The "wedging effect" and structural disjoining pressure quantitative validation is limited.

Response 2: We acknowledge this limitation and have revised the relevant section (Section 3.1) to include explicit assumptions for the disjoining pressure equation, with a new statement: "This equation is derived under the assumption of spherical nanoparticles in point contact with a flat solid surface..." We also added a cautionary note: "However, it should be noted that the actual disjoining pressure in porous media is influenced by multiple factors including particle concentration, packing geometry, and surface roughness, which may result in values different from idealized theoretical calculations [31]."

Comment 3: The role of surface charge, surfactant adsorption isotherms, and competitive adsorption is not sufficiently discussed.

Response 3: We have added substantial new content addressing these issues:

A new section on adsorption isotherm measurements with Langmuir model fitting (Section 2.3)

Detailed discussion of competitive adsorption dynamics including asphaltene-nanoparticle interactions (Section 3.3)

Quantitative data on asphaltene adsorption reduction in the presence of surfactant

Comment 4: Hydrogen bonding and specific adsorption should be considered for OP-10/SiO₂ interaction.

Response 4: We have expanded Section 2.2 and 3.3 to include discussion of hydrogen bonding between polyoxyethylene chains and silanol groups, with FTIR evidence cited showing shifts in Si-OH stretching vibration peaks upon OP-10 adsorption [29].

Comment 5: Distinguishing between experimental observation and conceptual illustration.

Response 5: We have added explicit notes to Figures 1 and 2 stating: "Note: This schematic represents a conceptual illustration of the proposed mechanisms based on experimental observations and theoretical analysis..."

Comment 6: Reducing speculative statements or supporting them with references.

Response 6: We have carefully reviewed the manuscript and either removed speculative statements or added supporting references. For example, claims about permeability-dependent performance are now supported by mechanistic explanations with references.

Comment 7: Experimental conditions in rheological experiments should be clearly stated.

Response 7: We have added detailed experimental conditions: "Interfacial rheological measurements were conducted using a stress-controlled rheometer (Anton Paar MCR 702) equipped with a bicone geometry at the oil-water interface. Measurements were performed at 70°C with oscillatory frequency sweeps from 0.01 to 10 Hz at a constant strain amplitude of 0.5%..."

Comment 8: The link between interfacial viscoelasticity and displacement performance should be discussed more critically.

Response 8: We have added a new paragraph explicitly connecting interfacial rheology to displacement performance through three mechanisms: emulsion stability during transport, resistance to shear-induced rupture, and facilitation of oil film detachment.

Comment 9: The reported emulsion droplet sizes (5–15 μm) are relatively large for pore-scale transport.

Response 9: We have added a comprehensive explanation addressing this apparent discrepancy, including: (1) dynamic breakup/coalescence during transport; (2) post-production coalescence; and (3) micro-emulsion transport followed by aggregation. We also added DLS data showing bimodal distribution immediately after collection.

Comment 10-14: Repetitive explanations, grammar, equation clarity, citation style, abbreviations.

Response10-14: We have:

Streamlined repetitive content throughout the manuscript

Conducted thorough grammar and spelling revision

Added clear assumptions and consistent units for all equations

Standardized citation format

Defined all abbreviations at first use (EOR, TEM, DLS, AFM, IFT, TDS, LCA, XPS, EDTA)

We have added 16 new references including recent publications from 2022-2025 to update the literature review.

Author Response File: Author Response.pdf

Reviewer 2 Report

Comments and Suggestions for Authors

This study investigates the synergistic enhancement of oil recovery in low-permeability reservoirs using a composite flooding system of silica (SiO₂) nanoparticles and a nonionic surfactant (OP-10). The research systematically optimizes the nanoparticle-to-surfactant ratio, elucidates the dual mechanisms of action and evaluates the system’s performance through laboratory experiments. It also assesses the economic viability, environmental impact, and field applicability of the composite technology. Before considered for publication, the following comments should be properly addressed.

• The behavior of ‘nanoparticle-surfactant’ system in the field-scale might be quite different from that in the lab-scale. You may want to validate the performance improvement in the large scale. For instance, will the optimal ratio of nanoparticle and surfactant be different?
• What each symbol in Figure 1 represents, e.g., which one denotes nanoparticle, surfactant, …? Same question applies to Figure 2.
• You may want to proof-read the whole manuscript to correct errors such as missing space in so many places.
• References in this manuscript are mostly old. The authors may want to re-review the literature for most recent relative work.
• It is helpful if you provide the TEM images and especially these for the nanoparticle-surfactant systems.
• What are the assumptions you made in the economic assessment? Please specify them explicitly and verify why they are reliable.
• You may want to imply how the minerals in the core will influence the performance of the ‘nanoparticle-surfactant’ system. The interaction between nanoparticle-mineral and surfactant-mineral surface play an important role.

Author Response

Comment 1: The behavior of 'nanoparticle-surfactant' system in the field-scale might be quite different from lab-scale. Will the optimal ratio be different?

Response 1: This is an excellent point. We have added a new section (Section 6.3) specifically addressing lab-to-field scale-up considerations, including:

Reservoir heterogeneity effects on optimal ratio

Residence time and flow path differences

Temperature and pressure gradients

Mixing and dilution effects

We explicitly state: "The optimal nanoparticle-surfactant ratio of 3:2 determined in laboratory studies may require adjustment based on specific formation characteristics. Pilot testing should include ratio sensitivity studies with variations of ±20% around the optimum."

Comment 2: Symbol explanations for Figures 1 and 2.

Response 2: We have added comprehensive symbol legends for both figures directly in the figure captions, explaining all components including nanoparticles, surfactant molecules (hydrophobic and hydrophilic portions), and other elements.

Comment 3: Proofreading for missing spaces and errors.

Response 3: We have conducted a thorough proofreading of the entire manuscript, correcting spacing errors and other typographical issues throughout.

Comment 4: References are mostly old; include recent work.

Response 4: We have updated the reference list significantly

Comment 5: Provide TEM images, especially for nanoparticle-surfactant systems.

Response 5: We have added references to TEM images in the Supplementary Materials section, including:

Figure S1: TEM images of SiO₂ nanoparticles

Figure S2: TEM images of nanoparticle-surfactant composite system showing surfactant corona layers

In the main text, we reference these figures in Sections 2.1 and 2.3.

Comment 6: Specify assumptions in economic assessment explicitly.

Response 6: We have completely revised Section 6.1 to include explicit assumptions with numbered listing:

(1) Sweep efficiency correction factor

(2) Well pattern geometry assumptions

(3) Oil price basis with sensitivity analysis

(4) Agent cost basis

(5) Optimal ratio stability considerations

Each assumption is now clearly stated with justification for reliability.

Comment 7: Address mineral-nanoparticle and mineral-surfactant interactions.

Response 7: We have added detailed discussion of mineral interactions in Section 3.1, including:

XRD mineralogical composition of core samples (quartz, feldspar, clay minerals)

Interaction mechanisms with quartz (Si-O-Si bridging, hydrogen bonding)

Different interaction mechanisms with clay minerals (kaolinite, illite)

Effects of surface charge variations on nanoparticle attachment

We have added relevant references [32,33] to support these discussions.

Author Response File: Author Response.pdf

Round 2

Reviewer 1 Report

Comments and Suggestions for Authors

Manuscript has been substantially improved and now is fully publishable

Reviewer 2 Report

Comments and Suggestions for Authors

It is recommended for publication in this fashion.