Comprehensive Review on the Role of Surfactants in the Chemical Enhanced Oil Recovery Process

Development and performance evaluation of multi-functional slickwater fracturing fluid system for shale reservoirs

The rapid decline in energy and production following the primary fracturing development of shale oil reservoirs, and the low production of single wells are the problems facing the development of Cangdong shale oil in the Bohai Bay Basin. A multi-functional fracturing fluid system with emulsification, viscosity reduction, oil washing, and wettability improvement was developed by introducing a mixed-charge surfactant (PSG) to environmentally friendly and low-cost slickwater fracturing fluid (SWFF). The evaluation focused on several key properties including temperature and shear resistance, interfacial activity, viscosity reduction, wettability, and oil washing, all of which were assessed through laboratory experiments. The results showed that the 0.2% PSG and SWFF have high compatibility, forming a functional fracturing fluid system that exhibits exceptional temperature and shear resistance, as well as high interfacial activity. The rate of emulsification and viscosity reduction between the system and GY734H shale oil exceeds 93.45%. Moreover, the system is completely demulsified after being left to stand at 70 °C for 2 h. Furthermore, the static oil washing efficiency of the functional fracturing fluid system at 80 °C is 20.99%, while the SWFF is only 11.65%, which confirms the indoor effectiveness of the system. With the further optimization and application of the multifunctional slickwater fracturing fluid system (SWFF + PSG), it is expected to play an important role in the efficient development of shale reservoirs in the Bohai Bay Basin.

Contamination and Cleaning of Ceramic Membrane in Phosphate Slurry Dewatering and Filtration Processes

Ceramic membrane dewatering and filtration technology is effective in reducing the water content of the phosphate slurry. However, membrane fouling remains an unavoidable issue. Herein, by investigating the mechanism of membrane contamination and developing innovative cleaning solutions, we can effectively address this issue. The main fouling form of ceramic membranes was observed to be complete blockage through analysis of the fouling process at various pollution time intervals by scanning electron microscopy (SEM) and mathematical model fitting. In addition, after cleaning severely contaminated membranes with a pollution rate of approximately 90%, a cleaning agent composed of surfactants, acid-washing agents, chelating agents, and auxiliaries was developed to address the phosphate contaminants. Owing to the combined effect of the detergent components, heavily soiled ceramic membranes can achieve a high flux recovery rate of over 90% after cleaning. This work offers new insights into ceramic membrane fouling and cleaning during phosphate slurry filtration.

β-Hydroxyl Group in the Sulfonic Biobased Zwitterionic Surfactant Improves Its Thermal Tolerance of Interfacial Activity

The hydrophilic head structure can significantly influence the interfacial performance of biobased zwitterionic surfactants. Among various hydrophilic groups, the hydroxyl group plays a considerable role in the influence on interfacial activity. However, the relevant mechanism remains to be elucidated. To study this point, in this work two new biobased zwitterionic surfactants, anisole-based oleamide ethyl hydroxypropyl sulfonyl quaternary ammonium salt (AEHSQA) and anisole-based oleamide ethyl sulfonylpropyl quaternary ammonium salt (AESPQA), were synthesized from biomass material methyl oleate, and the interfacial performances of the two surfactants were evaluated. It showed that AEHSQA can lower the interfacial tensions between crude oil and groundwater to the ultralow level (<10-2 mN/m) at a temperature of up to 120 °C and a concentration of Ca2+ of up to 2500 mg/L with one more β-hydroxyl group, while the corresponding tolerances of AESPQA are only 90 °C and 250 mg/L. Molecular dynamics simulation (MDS) was employed to study the interfacial behaviors of surfactant molecules at the oil-water interface under conditions of different temperatures and salinities. The results of MDS implied that introducing a hydroxyl group could improve the thermal resistance and salt tolerance of zwitterionic surfactants via resisting the hydrophilicity decline and interfacial looseness of surfactant molecules resulting from the increases in temperature and salinity.

Harnessing biochemical innovations for sustainable oil recovery: perspectives from the Indian context on green enhanced oil recovery (GEOR) methods for matured petroleum fields

Green enhanced oil recovery (GEOR) has emerged as an eco-friendly alternative to conventional oil recovery techniques, offering a more sustainable way to increase oil extraction while minimizing environmental harm. This review focuses on the potential of biochemicals, particularly biopolymers, and biosurfactants, in improving oil recovery in Indian oilfields. While these biochemicals, such as xanthan gum, scleroglucan, and HEC, have shown promising results in global oilfields, their application in India remains largely unexplored. By comparing the characteristics of Indian reservoirs with successful international case studies, this review highlights the feasibility and advantages of biopolymer-based EOR methods in India's unique reservoir conditions, including high temperatures, salinity, and other challenges. Despite the proven benefits of biopolymers, such as their environmental sustainability and operational efficiency, they have not yet been widely adopted in Indian oilfields. The review identifies key research gaps, including the need for a deeper understanding of microbial and biopolymer interactions, and stresses the importance of developing sustainable and cost-effective production methods for biopolymers. The findings suggest that integrating biopolymers into India's oil recovery processes could not only enhance extraction rates but also contribute to greener, more efficient practices. This review provides a comprehensive overview of the current state of biopolymer-based EOR and outlines future research directions, contributing to the development of more sustainable oil recovery techniques tailored to India's specific needs.

Advancements and challenges in the use of surfactants and nanoparticles for enhanced oil recovery: mechanisms, synergies, and field applications

This review highlights the recent advancements and challenges in the use of surfactants and nanoparticles for enhanced oil recovery (EOR). Novel surfactant formulations, including biosurfactants and hybrid systems, have shown improved recovery efficiency and environmental sustainability. Surfactant-polymer mixtures offer synergistic effects that enhance performance across various reservoir conditions. Concurrently, advancements in nanoparticle technology, such as green nanotechnology and improved formulations, have enhanced the stability, dispersion, and functionality of nanoparticles in EOR processes. Critical factors such as nanoparticle size, concentration, and surface modifications play pivotal roles in optimizing oil recovery efficiency. However, significant challenges persist, particularly surfactant adsorption onto rock surfaces and nanoparticle agglomeration, which reduce the overall effectiveness of these techniques. Addressing these limitations requires strategies such as surface modification and advanced delivery mechanisms. Additionally, economic and environmental concerns remain key barriers to large-scale implementation, underscoring the importance of sustainable and cost-effective solutions. A critical gap in the research is the lack of large-scale field studies and long-term monitoring, which are essential for validating laboratory findings and optimizing these technologies for real-world applications. With increasing focus on sustainability, future research is expected to prioritize eco-friendly materials and methods. Integrating surfactant and nanoparticle-based EOR with other recovery techniques, such as thermal and gas injection, holds potential for maximizing oil recovery. Continued research and development are crucial to overcoming current challenges and advancing the sustainability and efficiency of EOR technologies, contributing to a cleaner and more efficient future for oil recovery.

Surface modification of nanoparticles for enhanced applicability of nanofluids in harsh reservoir conditions: A comprehensive review for improved oil recovery

Nanoparticles improve traditional Enhanced Oil Recovery (EOR) methods but face instability issues. Surface modification resolves these, making it vital to understand its impact on EOR effectiveness. This paper examines how surface-modified nanoparticles can increase oil recovery rates. We discuss post-synthesis modifications like chemical functionalization, surfactant and polymer coatings, surface etching, and oxidation, and during-synthesis modifications like core-shell formation, in-situ ligand exchange, and surface passivation. Oil displacement studies show surface-engineered nanoparticles outperform conventional EOR methods. Coatings or functionalizations alter nanoparticle size by 1-5 nm, ensuring colloidal stability for 7 to 30 days at 25 to 65 °C and 30,000 to 150,000 ppm NaCl. This stability ensures uniform distribution and enhanced penetration through low-permeability (1-10 md) rocks, improving oil recovery by 5 to 50 %. Enhanced recovery is achieved through 1-25 μm oil-in-water emulsions, increased viscosity by ≥30 %, wettability changes from 170° to <10°, and interfacial tension reductions of up to 95 %. Surface oxidation is suitable for carbon-based nanoparticles in high-permeability (≥500 md) reservoirs, leading to 80 % oil recovery in micromodel studies. Surface etching is efficient for all nanoparticle types, and combining it with chemical functionalization enhances resistance to harsh conditions (≥40,000 ppm salinity and ≥ 50 °C). Modifying nanoparticle surfaces with a silane coupling agent before using polymers and surfactants improves EOR parameters and reduces polymer thermal degradation (e.g., only 10 % viscosity decrease after 90 days). Economically, 500 ppm of nanoparticles requires 56.25 kg in a 112,500 m3 reservoir, averaging $200/kg, and 2000 ppm of surface modifiers require 4 kg at $3.39/kg. This results in 188,694.30 barrels, or $16,039,015.50 at $85 per barrel for a 20 % increase in oil recovery. The economic benefits justify the initial costs, highlighting the importance of cost-effective nanoparticles for EOR applications.

Attachment and Detachment of Oil Droplets on Solid Surfaces: Insights from Molecular Simulations

The behavior of oil droplets at solid surfaces is a key aspect of oil production and environmental protection. In this paper, the mechanisms of attachment and detachment of oil aggregates are studied via molecular dynamics simulations. The influence of oil-surface interactions on the shape and structure of adsorbed clusters is discussed. Using selected shape metrics, we prove quantitatively that the shape of oil aggregates changes from almost spherical droplets, through multilayer structures, to monolayer films. The oil detachment from solid surfaces plays a major role in enhanced oil recovery. Here, we investigated oil droplet detachment from the solid surface immersed in Janus nanoparticle suspensions. The nanoparticle is modeled as a dimer built of segments that exhibit different affinities to oil and solvent molecules. Our results indicated that the adsorption of Janus dimers on the surface of oil droplets played an essential role in the oil removal processes. Stronger adsorption causes faster detachment of the oil droplet. Based on our findings, suspensions of Janus dimers can be considered to be high-performance agents in removing oil droplets from solid surfaces.

Reducing the assemblies of amyloid-beta multimers by sodium dodecyl sulfate surfactant at concentrations lower than critical micelle concentration: molecular dynamics simulation exploration

Amyloid-β peptide, the predominant proteinaceous component of senile plaques, is responsible for the incidence of Alzheimer's disease (AD), an age-associated neurodegenerative disorder. Specifically, the amyloid-β(1-42) (Aβ1-42) isoform, known for its high toxicity, is the predominant biomarker for the preliminary diagnosis of AD. The aggregation of the Aβ1-42 peptides can be affected by the components of the cellular medium through changing their structures and molecular interactions. In this study, we investigated the effect of sodium dodecyl sulfate (SDS) at much lower concentrations than the critical micelle concentration (CMC) on Aβ1-42 aggregation. For this purpose, we studied mono-, di-, tri- and tetramers of Aβ1-42 peptide in two different concentrations of SDS molecules (10 and 40 molecules) using a 300 ns molecular dynamics simulation for each system. The distance between the center of mass (COM) of Aβ1-42 peptides confirms that an increase in the number of SDS molecules decreases their aggregation probability due to greater interaction with SDS molecules. Besides, the less compactness parameter reveals the reduced aggregation probability of Aβ1-42 peptides. Based on the energetic FEL landscapes, SDS molecules with the concentration closer to the CMC are an effective inhibitory agent to prevent the formation of Aβ1-42 fibrils. Also, the aggregation direction of the peptide pairs can be predicted by determining the direction of the accumulation-deterrent forces.Communicated by Ramaswamy H. Sarma.

Synthesis of a novel carbon-based nano-emulsifier and its application in viscosity reduction of emulsified Jurassic oil in the Sichuan Basin

A study was undertaken into the emulsification and viscosity reduction processes of crude oil originating from the Jurassic formation of the Sichuan Basin. Central to this investigation was the successful synthesis of a carbon-based nano emulsifier named GOPH, utilizing graphene oxide as substrate and hydrophilic alkyl glycidyl ether and polyoxyethylene ether as modifiers. The structural integrity of this nano-emulsifier was comprehensively characterized via Fourier transform infrared spectroscopy, scanning electron microscopy, and thermogravimetric analysis. Notably, GOPH nanofluids exhibited a remarkable merit in decreasing the oil/water interfacial tension from 31.96 mN m-1 to a low value of 9.76 mN m-1 with a critical concentration of 45 ppm. Moreover, interfacial film folding experiments revealed that GOPH nanoparticles "jammed" at the oil-water interface, forming a robust film. When Jurassic crude oil was the oil phase, and GOPH nanofluids were introduced into the water phase, the crude oil was successfully induced to form a low-viscosity oil-in-water (O/W) emulsion. Emulsion droplet size and viscosity measurements demonstrated that this emulsion possessed small size distributions with remarkable stability, achieving a viscosity reduction of up to 91.6% at a water content of 80%. The underlying mechanism for this phenomenon mainly lies in the interaction between the carbon-based nano-emulsifier and asphaltene, which form a composite unit, enabling the construction of a flexible interfacial film that significantly stabilizes the O/W emulsion.

Functional surfactant-directing ultrathin metallic nanoarchitectures as high-performance electrocatalysts

Ultrathin nanosheets possess a distinctive structure characterized by an abundance of active sites fully accessible on their surface. Concurrently, their nanoscale thickness confers an extraordinarily high specific surface area and promising electronic properties. To date, numerous strategies have been devised for synthesizing precious metal nanosheets that exhibit excellent electrocatalytic performance. In this paper, recent progress in the controlled synthesis of two-dimensional, ultrathin nanosheets by a self-assembly mechanism using functional surfactants is reviewed. The aim is to highlight the key role of functional surfactants in the assembly and synthesis of two-dimensional ultrathin nanosheets, as well as to discuss in depth how to enhance their electrochemical properties, thereby expanding their potential applications in catalysis. We provide a detailed exploration of the mechanisms employed by several long-carbon chain surfactants commonly used in the synthesis of nanosheets. These surfactants exhibit robust electrostatic and hydrophobic effects, effectively confining the crystalline growth of metals along lamellar micelles. Moreover, we present an overview of the electrocatalytic performance demonstrated by the ultrathin nanosheets synthesized through this innovative pathway. Furthermore, it offers valuable insights that may pave the way for further exploration of more functional long-chain surfactants, leading to the synthesis of ultrathin nanosheets with significantly enhanced electrocatalytic performance.

Advancements in Surfactant Carriers for Enhanced Oil Recovery: Mechanisms, Challenges, and Opportunities

Enhanced oil recovery (EOR) techniques are crucial for maximizing the extraction of residual oil from mature reservoirs. This review explores the latest advancements in surfactant carriers for EOR, focusing on their mechanisms, challenges, and opportunities. We delve into the role of inorganic nanoparticles, carbon materials, polymers and polymeric surfactants, and supramolecular systems, highlighting their interactions with reservoir rocks and their potential to improve oil recovery rates. The discussion includes the formulation and behavior of nanofluids, the impact of surfactant adsorption on different rock types, and innovative approaches using environmentally friendly materials. Notably, the use of metal oxide nanoparticles, carbon nanotubes, graphene derivatives, and polymeric surfacants and the development of supramolecular complexes for managing surfacant delivery are examined. We address the need for further research to optimize these technologies and overcome current limitations, emphasizing the importance of sustainable and economically viable EOR methods. This review aims to provide a comprehensive understanding of the emerging trends and future directions in surfactant carriers for EOR.

Rheological behavior and solution pH response properties of nanoparticle-regulated low surface tension systems

Regarding the rheological properties of fluids, certain nanoparticles can markedly modify the rheological behavior of low surface tension solutions by interacting with surfactant molecules. In this work, a low surface tension fluid with cetyltrimethylammonium chloride was prepared, and the silica nanoparticles were uniformly dispersed into it by ultrasonic dispersion. By adjusting the size, shape, and concentration of nanoparticles, the fluid behavior can be changed from Newtonian to non-Newtonian with finely tuned viscosity and characterized by a shear-thinning rheological behavior. In addition, this work explored how variations in environmental temperature and solution pH affect the rheological responses of the low surface tension suspension system. The experimental findings revealed that increasing the temperature substantially decreases the system's viscosity and induces a shear-thickening behavior. It is particularly significant that, under extreme pH conditions (either strongly acidic or alkaline), the viscosity of the nanoparticle suspensions was markedly enhanced at a particle concentration of 10 000 ppm. This interesting result coincided with a notable reduction in the zeta potential and an increase in the average particle size, suggesting an intensified aggregation of particles within the suspension system. A mechanism detailing the interaction between silica nanoparticles and surfactant micelles was proposed. This work indicates that the incorporation of nanoparticles into surfactant solutions offers a powerful approach to modulating fluid rheology across various conditions.

Unveiling the revolutionary role of nanoparticles in the oil and gas field: Unleashing new avenues for enhanced efficiency and productivity

Prominent oil corporations are currently engaged in a thorough examination of the potential implementation of nanoparticles within the oil and gas sector. This is evidenced by the substantial financial investments made towards research and development, which serves as a testament to the significant consideration given to nanoparticles. Indeed, nanoparticles has garnered increasing attention and innovative applications across various industries, including but not limited to food, biomedicine, electronics, and materials. In recent years, the oil and gas industry has conducted extensive research on the utilization of nanoparticles for diverse purposes, such as well stimulation, cementing, wettability, drilling fluids, and enhanced oil recovery. To explore the manifold uses of nanoparticles in the oil and gas sector, a comprehensive literature review was conducted. Reviewing several published study data leads to the conclusion that nanoparticles can effectively increase oil recovery by 10 %-15 % of the initial oil in place while tertiary oil recovery gives 20-30 % extra initial oil in place. Besides, it has been noted that the properties of the reservoir rock influence the choice of the right nanoparticle for oil recovery. The present work examines the utilization of nanoparticles in the oil and gas sector, providing a comprehensive analysis of their applications, advantages, and challenges. The article explores various applications of nanoparticles in the industry, including enhanced oil recovery, drilling fluids, wellbore strengthening, and reservoir characterization. By delving into these applications, the article offers a thorough understanding of how nanoparticles are employed in different processes within the sector. This analysis may prove highly advantageous for future studies and applications in the oil and gas sector.

Enhanced interfacial activity by maximizing synergy between long-chain ionic liquid and conventional surfactant for enhanced oil recovery

Conventional surfactants encounter limitations for application in oil reservoirs; however, combining surface-active ionic liquids (SAILs) with conventional surfactants presents an opportunity to enhance the interfacial properties of crude oil-water systems, giving also economic benefits. Accordingly, blends of a long-chain cationic imidazolium-based SAIL, namely, 1-dodecyl-3-methylimidazolium chloride, [C12mim][Cl], and the anionic conventional surfactant, sodium dodecyl sulfate were investigated here. Initial experiments with individual surfactants revealed efficient adsorption and consistent adsorption parameters. Subsequently, the use of mixtures showed synergistic effects for interfacial tension reduction of up to 86.0%, and critical micelle concentration reduction of 72.1% compared to the linear contribution of individual components. These improvements were observed at the optimal SAIL mole fraction of 0.3 and the mixture concentration of 0.003 mol dm-3, resulting in interfacial tension reduction from 29.1 to 1.6 mN m-1 as well as achieving a low critical micelle concentration of 2.7 × 10-3 mol dm-3 coinciding with 83.6% synergy. These findings underscore the favorable interactions between oppositely charged components in the mixtures, amplifying their activity beyond the linear contributions of the individual surfactants. Additionally, theoretical assessments using the Gibbs adsorption equation and the Rosen model provided insight into the adsorption behavior of both the individual surfactants and their mixtures, together with reasonable variations in the corresponding parameters.

Effective Synergistic Action of Benzimidazolium Nano Gemini Ionic Liquid and Conventional Surfactant for Chemical Enhanced Oil Recovery

Blends of newly developed Gemini surface-active ionic liquids (GSAILs) and conventional surfactants offer significant enhancements to the interfacial properties between crude oil and water, providing economic benefits in chemically enhanced oil recovery. In this study, the mixtures of a benzimidazolium cationic GSAIL, [C4benzim-C6-benzimC4][Br2], and sodium dodecyl benzenesulfonate (SDBS) were successfully utilized for improving crude oil-water interfacial properties. The research revealed synergistic effects of up to 99.6% in reducing interfacial tension (IFT), achieving a low IFT value of 0.04 mN m-1 corresponding to an optimal GSAIL mole fraction of 0.2 for the mixture of surfactants. Additionally, significant synergies of 53.4 and 74% were observed in oil-water emulsification and in surface wettability when using a GSAIL mole fraction of 0.2. These results showcase the importance of the dominant interaction between the opposite-charged surfactants. The Frumkin isotherm and the Rosen model were employed for the theoretical study of adsorption behavior of individual surfactants and their mixture at the interface, demonstrating reasonable parameter variations. The overall findings emphasize the potential of utilizing these unique blends to enhance oil recovery processes through tailored interfacial properties.

Exploring fungal bioemulsifiers: insights into chemical composition, microbial sources, and cross-field applications

The demand for emulsion-based products is crucial for economic development and societal well-being, spanning diverse industries such as food, cosmetics, pharmaceuticals, and oil extraction. Formulating these products relies on emulsifiers, a distinct class of surfactants. However, many conventional emulsifiers are derived from petrochemicals or synthetic sources, posing potential environmental and human health risks. In this context, fungal bioemulsifiers emerge as a compelling and sustainable alternative, demonstrating superior performance, enhanced biodegradability, and safety for human consumption. From this perspective, the present work provides the first comprehensive review of fungal bioemulsifiers, categorizing them based on their chemical nature and microbial origin. This includes polysaccharides, proteins, glycoproteins, polymeric glycolipids, and carbohydrate-lipid-protein complexes. Examples of particular interest are scleroglucan, a polysaccharide produced by Sclerotium rolfsii, and mannoproteins present in the cell walls of various yeasts, including Saccharomyces cerevisiae. Furthermore, this study examines the feasibility of incorporating fungal bioemulsifiers in the food and oil industries and their potential role in bioremediation events for oil-polluted marine environments. Finally, this exploration encourages further research on fungal bioemulsifier bioprospecting, with far-reaching implications for advancing sustainable and eco-friendly practices across various industrial sectors.

Zwitterions and betaines as highly soluble materials for sustainable corrosion protection: Interfacial chemistry and bonding with metal surfaces

The primary requirements for interfacial adsorption and corrosion inhibition are solubility and the existence of polar functional groups, particularly charges. Traditional organic inhibitors have a solubility issue due to the hydrophobic moieties they incorporate. Most documented organic inhibitors have aromatic rings, hydrocarbon chains, and a few functional groups. The excellent solubility and high efficacy of zwitterions and betaines make them the perfect replacements for insoluble corrosion inhibitors. Zwitterions and betaines are more easily soluble because of interactions between their positive and negative charges (-COO-, -PO3-, -NH3, -NHR2, -NH2R, -SO3- etc.) and the polar solvents. The positive and negative charges also aid these molecules' physical and chemical adsorption at the metal-electrolyte interfaces. They develop a corrosion-inhibiting layer through their adsorption. After becoming adsorbed at the metal-electrolyte interface, they act as mixed-type inhibitors, slowing both cathodic and anodic processes. They usually adsorb according to the Langmuir adsorption isotherm. In this article, the corrosion inhibition potential of zwitterions and betaines in the aqueous phase, as well as their mode of action, are reviewed. This article details the advantages and disadvantages of utilizing zwitterions and betaines for sustainable corrosion protection.

New Trends in Biosurfactants: From Renewable Origin to Green Enhanced Oil Recovery Applications

Enhanced oil recovery (EOR) processes are technologies used in the oil and gas industry to maximize the extraction of residual oil from reservoirs after primary and secondary recovery methods have been carried out. The injection into the reservoir of surface-active substances capable of reducing the surface tension between oil and the rock surface should favor its extraction with significant economic repercussions. However, the most commonly used surfactants in EOR are derived from petroleum, and their use can have negative environmental impacts, such as toxicity and persistence in the environment. Biosurfactants on the other hand, are derived from renewable resources and are biodegradable, making them potentially more sustainable and environmentally friendly. The present review intends to offer an updated overview of the most significant results available in scientific literature on the potential application of biosurfactants in the context of EOR processes. Aspects such as production strategies, techniques for characterizing the mechanisms of action and the pros and cons of the application of biosurfactants as a principal method for EOR will be illustrated and discussed in detail. Optimized concepts such as the HLD in biosurfactant choice and design for EOR are also discussed. The scientific findings that are illustrated and reviewed in this paper show why general emphasis needs to be placed on the development and adoption of biosurfactants in EOR as a substantial contribution to a more sustainable and environmentally friendly oil and gas industry.

Static and dynamic adsorption of a gemini surfactant on a carbonate rock in the presence of low salinity water

In chemical enhanced oil recovery (cEOR) techniques, surfactants are extensively used for enhancing oil recovery by reducing interfacial tension and/or modifying wettability. However, the effectiveness and economic feasibility of the cEOR process are compromised due to the adsorption of surfactants on rock surfaces. Therefore, surfactant adsorption must be reduced to make the cEOR process efficient and economical. Herein, the synergic application of low salinity water and a cationic gemini surfactant was investigated in a carbonate rock. Firstly, the interfacial tension (IFT) of the oil-brine interface with surfactant at various temperatures was measured. Subsequently, the rock wettability was determined under high-pressure and high-temperature conditions. Finally, the study examined the impact of low salinity water on the adsorption of the cationic gemini surfactant, both statically and dynamically. The results showed that the low salinity water condition does not cause a significant impact on the IFT reduction and wettability alteration as compared to the high salinity water conditions. However, the low salinity water condition reduced the surfactant's static adsorption on the carbonate core by four folds as compared to seawater. The core flood results showed a significantly lower amount of dynamic adsorption (0.11 mg/g-rock) using low salinity water conditions. Employing such a method aids industrialists and researchers in developing a cost-effective and efficient cEOR process.

Synthesis of Polyether Carboxylate and the Effect of Different Electrical Properties on Its Viscosity Reduction and Emulsification of Heavy Oil

Heavy oil exploitation needs efficient viscosity reducers to reduce viscosity, and polyether carboxylate viscosity reducers have a significant viscosity reduction effect on heavy oil. Previous work has studied the effect of different side chain lengths on this viscosity reducer, and now a series of polyether carboxylate viscosity reducers, including APAD, APASD, APAS, APA, and AP5AD (the name of the viscosity reducer is determined by the name of the desired monomer), with different electrical properties have been synthesized to investigate the effect of their different electrical properties on viscosity reduction performance. Through the performance tests of surface tension, contact angle, emulsification, viscosity reduction, and foaming, it was found that APAD viscosity reducers had the best viscosity reduction performance, reducing the viscosity of heavy oil to 81 mPa·s with a viscosity reduction rate of 98.34%, and the worst viscosity reduction rate of other viscosity reducers also reached 97%. Additionally, APAD viscosity reducers have the highest emulsification rate, and the emulsion formed with heavy oil is also the most stable. The net charge of APAD was calculated from the molar ratio of the monomers and the total mass to minimize the net charge. While the net charge of other surfactants was higher. It shows that the amount of the surfactant's net charge affects the surfactant's viscosity reduction effect, and the smaller the net charge of the surfactant itself, the better the viscosity reduction effect.

Rhamnolipid Self-Aggregation in Aqueous Media: A Long Journey toward the Definition of Structure–Property Relationships

The need to protect human and environmental health and avoid the widespread use of substances obtained from nonrenewable sources is steering research toward the discovery and development of new molecules characterized by high biocompatibility and biodegradability. Due to their very widespread use, a class of substances for which this need is particularly urgent is that of surfactants. In this respect, an attractive and promising alternative to commonly used synthetic surfactants is represented by so-called biosurfactants, amphiphiles naturally derived from microorganisms. One of the best-known families of biosurfactants is that of rhamnolipids, which are glycolipids with a headgroup formed by one or two rhamnose units. Great scientific and technological effort has been devoted to optimization of their production processes, as well as their physicochemical characterization. However, a conclusive structure–function relationship is far from being defined. In this review, we aim to move a step forward in this direction, by presenting a comprehensive and unified discussion of physicochemical properties of rhamnolipids as a function of solution conditions and rhamnolipid structure. We also discuss still unresolved issues that deserve further investigation in the future, to allow the replacement of conventional surfactants with rhamnolipids.

Synthesis, Self-Assembly Properties, and Degradation Characterization of a Nonionic Photocleavable Azo-Sulfide Surfactant Family

We report the synthesis and characterization of a new family of maltose-derived nonionic surfactants that contain a photocleavable azo-sulfide linker (mAzo). The self-assembly properties of these surfactants were investigated using surface tension measurements to determine the critical micelle concentration (CMC), dynamic light scattering (DLS) to reveal the hydrodynamic radius of their self-assemblies, and transmission electron microscopy (TEM) to elucidate the micelle morphology. Ultraviolet-visible (UV-visible) spectroscopy confirmed the rapid photodegradation of these surfactants, but surface tension measurements of the surfactant solutions before and after degradation showed unusual degradation products. The photodegradation process was further studied using online liquid chromatography coupled with mass spectrometry (LC-MS),which revealed that these surfactants can form another photo-stable surfactant post-degradation. Finally, traditionally challenging proteins from heart tissue were solubilized using the mAzo surfactants to demonstrate their potential in biological applications.

Observation of Strong Synergy in the Interfacial Water Response of Binary Ionic and Nonionic Surfactant Mixtures

Interfacial vibrational footprints of the binary mixture of sodium dodecyl sulfate (SDS) and hexaethylene glycol monododecyl ether (C₁₂E₆) were probed using heterodyne detected vibrational sum frequency generation (HDVSFG). Our results show that in the presence of C₁₂E₆ at CMC (70 μM) the effect of SDS on the orientation of interfacial water molecules is enhanced 10 times compared to just pure surfactants. The experimental results contest the traditional Langmuir adsorption model predictions. This is also evidenced by our molecular dynamics simulations that show a remarkable restructuring and enhanced orientation of the interfacial water molecules upon DS^- adsorption to the C₁₂E₆ surface. The simulations show that the adsorption free energy of DS^- ions to a water surface covered with C₁₂E₆ is an enthalpy-driven process and more attractive by ∼10 k_BT compared to the adsorption energy of DS^- to the surface of pure water.

Molecular dynamics simulation study of adsorption of anionic–nonionic surfactants at oil/water interfaces

Four anionic–nonionic surfactants with the same headgroups and different units of oxygen ethyl (EO) and oxygen propyl (PO) were adopted to investigate the influence on oil/water interfacial tensions in this article. Molecular dynamics (MD) simulations were conducted to study the interfacial property of the four surfactants. Four parameters were proposed to reveal the effecting mechanism of molecular structure on interfacial tension, which included the interfacial thickness, order parameter of the hydrophobic chain, radial distribution function, and the solvent accessible surface area. In addition, the electrostatic potential of the four surfactants was calculated. The research results indicated that the interface facial mask formed by the surfactants, which contained three EO or three PO units was more stable, and it was easier for the surfactants of six EO or six PO units to form a microemulsion at higher concentrations. The adsorption mechanism of the anionic–nonionic surfactant systems at the oil/water interfaces was supplemented at a molecular level, which provided fundamental guidance for an in-depth understanding of the optimal selection of the surfactants in enhancing oil recovery.

Four anionic–nonionic surfactants with the same headgroups and different units of oxygen ethyl (EO) and oxygen propyl (PO) were adopted to investigate the influence on oil/water interfacial tensions in this article.