Conversion of Waste Cooking Oil to Environmentally Acceptable Surfactants for Enhanced Oil Recovery

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M. AlSabagh, Fatma H. Abdel-Salam, Asmaa Mohamed This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8595521/v1 This work is licensed under a CC BY 4.0 License Status: Under Revision Version 1 posted 14 You are reading this latest preprint version Abstract Enhanced oil recovery (EOR) is a tertiary method used to extract crude oil remaining in reservoirs. With growing concerns about waste generation and its environmental impacts, waste cooking oil (WCO) has emerged as both a pollutant and a valuable renewable feedstock. WCO can be efficiently converted into sustainable surfactants with favorable surface and interfacial properties suitable for reservoir conditions. In this study, anionic and nonionic surfactants were synthesized from WCO: ethoxylated dodecylbenzene sulfonate (EABS14, aromatic) and ethoxylated hydrolyzed waste oil (EHWO14, aliphatic). Isopropanol was incorporated as a co-surfactant to enhance microemulsion performance. Phase behavior was evaluated at salinities of 50×10³, 100×10³, and 200×10³ ppm and at temperatures of 50 and 70°C. Solubilization parameters and microemulsion phase volumes were used to determine optimal conditions. At optimum salinity, dynamic interfacial tension (IFT) decreased significantly, reaching 1×10⁻², 8×10⁻², and 1×10⁻³ mN/m for EHWO14, EHWO14 + EABS14, and EHWO14 + EABS14+CS, respectively. Contact angles were reduced from 155° to 27°, 35°, and 22°, indicating effective wettability alteration. Flooding experiments confirmed the efficiency of WCO-derived surfactants, with maximum oil recovery at 100×10³ ppm and 50°C. Recovery factors were 71.00% for EHWO14, 73.33% for EHWONa, 72.91% for EHWONa+EHWO14, and highest at 79.00% for the EHWO14 + EABS14+CS blend. These results demonstrate that WCO valorization into surfactants provides an eco-friendly and effective EOR alternative. Physical sciences/Chemistry Physical sciences/Energy science and technology Physical sciences/Engineering Earth and environmental sciences/Environmental sciences (Ecofriendly surfactants Waste cooking oil phase behavior Interfacial tension Enhanced oil recovery) Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 1. Introduction The oil and gas sectors are looking for improved oil recovery strategies to increase the recovery of oil from reservoirs. Injecting chemical slugs into oil reservoirs is a well-established EOR method [ 1 – 4 ]. The most common variants of this method involve injecting slugs containing surfactant, alkaline surfactant, or alkaline-surfactant-polymer (ASP) [ 5 – 9 ]. By adjusting the injected fluid's parameters, each additive in the chemical slug enhances the EOR mechanisms, such as interfacial tension (IFT) reduction, wettability alteration, and mobility ratio control [ 10 – 13 ]. Because microemulsions can significantly reduce the IFT between water and oil, they play crucial role in EOR applications. In reservoir rock pores, microemulsions can effectively mobilize trapped oil by overcoming capillary forces. During microemulsion flooding, surfactants and co-surfactants are injected to form a middle-phase microemulsion, achieving ultra-low interfacial tension (IFT) between 10 − 3 and 10 − 4 mNm − 1 . Microemulsions significantly enhance oil recovery due to their large specific surface area, smaller droplet size, low IFT, unique solubility, and penetration properties. The microemulsion evaluation methodology comprises core flooding experiments, stability analysis, and interfacial tension measurements. There are four types of microemulsions according to the Winsor classification: Type I (oil-in-water, O/W), Type II (water-in-oil, W/O), Type III (bi continuous middle phase), and Type IV (single-phase isotropic solution). In Winsor Type I systems, oil becomes solubilized in the aqueous phase through encapsulation by surfactant tails forming micellar structures. Winsor Type II systems consist of reverse micelles that solubilize water within the continuous oil phase. Winsor Type III systems exhibit a bi continuous middle phase where surfactant molecules form interconnected networks between oil and water domains. In this bi continuous phase, both oil and water become molecularly dispersed. Winsor Type IV occurs when sufficient surfactants completely solubilize all water and oil components into a single isotropic solution. Compared to Winsor Type I and II, Winsor Type III and Type IV microemulsions demonstrate superior interfacial tension (IFT) reduction between oil and water phases [ 14 , 15 ]. Low interfacial tension (IFT) indicates high mutual solubility between oil and water phases. For effective EOR development, three critical factors must be addressed: accurate characterization of reservoir rock wettability, optimal control of surfactant adsorption, and efficient IFT reduction at oil-water interfaces. Surfactant chemistry plays a pivotal role in achieving these interfacial modifications by controlling molecular interactions at fluid-fluid and fluid-rock interfaces. Surfactant molecules are essential for controlling IFT in enhanced oil recovery applications. Surfactant molecules modify interfacial molecular interactions through adsorption at liquid-liquid interfaces, reducing repulsive forces and stabilizing the system by minimizing interfacial energy. The aqueous solution contains surfactant monomers that adsorb at interfaces, forming a monolayer which reduces both surface and interfacial tension. At specific concentrations, surfactant monomers form a closed aggregate (micelle), with the hydrophobic tails preserved from water and the hydrophilic heads facing it. This transition point is defined as the critical micelle concentration (CMC), a key surfactant property [ 16 , 17 ]. Surfactant injection has been successfully implemented in oilfield applications. Optimizing both concentration and selecting appropriate surfactants as key components of chemical slugs are critical for effectively mobilizing residual oil trapped in reservoir pore spaces. The surfactants are typically introduced into the injected water to achieve significant interfacial tension reduction between oil and water phases. Since surfactant performance and stability vary significantly with reservoir conditions, comprehensive EOR laboratory testing is essential to quantify surfactant efficiency prior to field implementation. The application of bio-based surfactants has gained significant attention in recent years. Researchers are increasingly investigating novel natural sources for surfactant production, motivated by their cost-effectiveness, abundant availability, and environmental sustainability [ 18 – 23 ]. For example, a castor oil-derived surfactant demonstrated exceptional performance by achieving ultra-low interfacial tension and effectively altering sandstone wettability from oil-wet to strongly water-we [ 3 , 23 , 24 ]. The surfactants have stable foam and emulsion properties [ 25 ]. To overcome the drawbacks of chemical surfactants, such as their high cost and environmental incompatibility, research into bio-based surfactants is ongoing. From both scientific and commercial perspectives, biosurfactants offer benefits such as sustainability and environmental friendliness [ 26 ]. Additional benefits of natural surfactants include low toxicity, high biodegradability, and greater accuracy and efficacy at high pH and temperature [ 27 ]. Various studies on the use of waste materials in EOR were reviewed, including those on environmentally safe potassium-doped graphene oxide particles made from oak fruit waste. These raw materials are abundant, cost-effective, biocompatible, biodegradable, and readily accessible. Interfacial tension, critical micelle concentration, and zeta potential were measured to assess the stability of particles treated with different surfactants. Adsorption experiments subsequently quantified surfactant loss during the flooding process [ 28 ]. A further investigation found that reduced graphene oxide, synthesized using waste plastic as a carbon source, enhanced the EOR process. These materials exhibit superior electrical, mechanical, and thermal properties because the synthesized graphene has a larger surface area than conventional metal oxide nanoparticles, resulting in higher surface activity. Converting solid waste into valuable carbon-based nanomaterials is a vital strategy for solid waste management [ 29 ]. Additionally, red onion skin, an agricultural waste biomass, was chosen as a natural recovery agent. This agricultural waste is a crucial source of quercetin, flavones, anthocyanins, and polyphenolics. Red onion skin was treated with glutaraldehyde in an aqueous sodium hydroxide solution and its efficacy was assessed in a sandstone core [ 30 ]. Another study was conducted to investigate the interactions of a biopolymer (animal glue) and a surfactant (lauryl ether sulfate) with hydrolyzed polyacrylamide. Several laboratory floods using steam, surfactant, biopolymer, and polymer were conducted individually and in combination on a semi-pilot model [ 31 ]. Many studies offer a critical evaluation of various green innovations for enhanced oil recovery, including organic materials injection, nanotechnology application, solar energy integration, microbial processes, water alternating gas, foam injection, and nanofluid injection, all contributing to a cleaner environment [ 32 ]. Researchers focus on the various advantages of green nanocomposites in EOR, primarily their safety for living things. As they are derived from plants or other safe industrial resources, these nanocomposites represent a highly attractive alternative EOR technique [ 33 ]. In another study, zinc oxide nanoparticles, which can prevent asphaltene deposition, reduce interfacial tension, and alter wettability, were combined with green nanocomposites in porous media for enhanced oil recovery [ 34 ]. Waste cooking oil (WCO) is a non-edible oil produced in large amounts. Its careless disposal may have a detrimental effect on humanity and the environment [ 35 ]. In this work, a natural bio-based surfactant will be prepared from waste cooking oil, a renewable source. The study's objectives include synthesizing this surfactant and evaluating its performance through critical micelle concentration (CMC) measurements, water-oil interfacial tension (IFT) analysis, wettability tests, ideal salinity determination, phase behavior observation, and oil recovery tests for enhanced oil recovery (EOR) applications. 2. Materials and Methods 2.1 Materials 2.1.1 Surfactants The anionic and nonionic surfactants used in this study were prepared from waste cooking oil [ 36 ]. The surfactants used in this study are: Ethoxylated Hydrolyzed Waste Oil (eo = 9) [EHWO9], Ethoxylated Hydrolyzed Waste Oil (eo = 14) [EHWO14], Ethoxylated Hydrolyzed Waste Oil (eo = 23) [EHWO23], Ethoxylated Hydrolyzed Waste Oil (eo = 46) [EHWO46], and Hydrolyzed Waste Oil sodium salt [HWONa]. 2.1.2 Crude oil The crude oil used for preparing microemulsions was sourced from the West Desert, Egypt, and provided by the General Petroleum Company (GPC). The oil had an API gravity of 27° at 15.55°C and a density of 0.8983 at 15°C. Its composition, determined by SARA analysis, was 57 wt% saturates, 21 wt% aromatics, 15 wt% resins, and 7.63 wt% asphaltenes. 2.1.3 Formation water Formation water, obtained from GPC, was used to prepare microemulsions under reservoir conditions. The water had a total dissolved solids (TDS) content of 200 × 10³ ppm. This formation water was diluted with distilled water to achieve lower salinities of 50 × 10³ and 100 × 10³ ppm. 2.1.4 The used Sand in the Sand-Packed Model Sand of various sizes (12, 18, and 20 mesh, corresponding to 1.68, 1.00, and 0.841 mm, respectively) was used to pack the model for the chemical flooding test to achieve a porosity of 25%. 2.2 Methods 2.2.1 The Used Surfactant Previous work involved preparing and characterizing surfactants extracted from waste cooking oil. The investigation included measuring surface tension, interfacial tension (IFT), estimating the critical micelle concentration (CMC), and determining thermodynamic properties [ 36 ]. 2.2.2 Preparation of Microemulsions The procedure for microemulsion stability testing was as follows. Surfactant solutions were prepared at a concentration of 0.25% in formation water with salinities of 50 × 10³ ppm, 100 × 10³ ppm, and 200 × 10³ ppm. Equal volumes of crude oil and surfactant solution were placed in graduated test tubes with rubber caps. The tubes were shaken by hand 60 times at a steady rate (completed within one minute) and were then allowed to settle for 24 hours. To investigate the impact of temperature, duplicate sets of tubes for each salinity were incubated at 25°C, 50°C, and 70°C. The entire experiment was performed in triplicate to ensure reproducibility. 2.2.3 Solubilization Parameters and Relative Phase Volume The phase behavior of the microemulsions was investigated using solubilization parameters. These parameters were calculated based on the volume of oil and water solubilized in the middle phase under ambient conditions. In the test tubes, a three-phase system was observed: an aqueous phase at the bottom, a microemulsion phase in the middle, and an oil phase at the top. This middle microemulsion phase is effective for oil recovery due to its ultra-low interfacial tension (IFT), which enables it to solubilize trapped oil from reservoir porous media. The solubilized oil volume was calculated using Eq. 1. Vo = V oi -V of (1) Where Vo represents the volume of solubilized oil in the microemulsion region, V oi represents the initial volume of the used oil, and V of represents the volume of oil in the upper phase. Similarly, the volume of water can be calculated using Eq. 2. Vw = V wi -V wf (2) Where Vw denotes the volume of solubilized water in the microemulsion region, Vwi denotes the initial volume of the used water, and Vwf denotes the volume of water in the lower phase. The solubilization values of oil and water were calculated using Eqs. 3, 4. SPo = Vo/Vs (3) SPw = Vw/Vs (4) Where SPo and SPw are the solubilization parameters of oil and water, and Vs is the volume of surfactant in the middle phase. The surfactant volume, Vs, is constant in the middle-phase microemulsion. On a solubilization curve, the point where the oil and water solubilization ratios are equal is crucial, as it identifies the optimal salinity. At this optimal salinity, equal amounts of oil and water are solubilized into the middle phase, forming a Type III microemulsion system. 2.2.4 Phase Diagram The solubilization method was used to construct triangular pseudo-ternary phase diagrams at room temperature (25°C). Surfactant (at a fixed mass), oil, and brine (pseudo-components) made up the triangle's three vertices. The experiments were set up using volumetric measurements, and the results were expressed as weight percentages. 2.2.5 Oil-water IFT Interfacial tension (IFT) between crude oil and surfactant solutions was measured at critical micelle concentration (CMC) and 50°C. To determine the optimal salinity, IFT tests were conducted at various salinity concentrations (50 × 10 3 ppm, 100 × 10 3 ppm, and 200 × 10 3 ppm). 2.2.6 Contact Angle Experiments The wettability of the reservoir model was examined by measuring the contact angle between crude oil and sand particles. These measurements, which indicate wettability alteration, were conducted using a High-Pressure Chamber (Attention Theta model) via the sessile drop method (ASTM/ISO 19403-5). The device measured the contact angle at the interfaces between the crude oil, brine/surfactant solution, and the core surface. All measurements were conducted at a constant temperature of 50°C. Sandstone samples were cut into thin sections approximately 2.5 mm thick to observe the penetration and spreading of oil droplets. The sections were first cleaned with high-pressure nitrogen gas and then aged in toluene solvent for 24 hours to remove contaminants, such as fatty acids from hand contact. Finally, to achieve a hydrophobic surface, the sections were heated to 50°C in crude oil. Contact angle measurements were performed at the critical micelle concentration (CMC) of the surfactant solution and recorded at various time intervals. A section holder was used to suspend the rock sample in the aqueous medium, positioning it a short distance from the needle. The associated software then automatically calculated the contact angle by drawing tangent lines to the droplet at the rock surface interface. 2.2.7 Emulsion Stability The stability of emulsions prepared with the surfactant solution was tested at its critical micelle concentration (CMC), with varying salinity and co-surfactant concentrations, and at different temperatures. Test tubes containing the prepared microemulsions were placed in water baths at 50°C and 70°C to monitor their stability over time. 2.2.8 Surfactants Slug Injection The core flooding procedure was conducted as follows: the model was first saturated with water. This was followed by oil injection to establish initial oil saturation, and then brine flooding until a 98% water cut was achieved. Next, a 1 PV surfactant slug—prepared at the critical micelle concentration (CMC) and the reservoir's optimum salinity—was injected. Finally, brine was re-injected until the water cut reached 99%. A chemical flooding system was used to evaluate the performance of the green microemulsion. A schematic diagram of the surfactant flooding apparatus is shown in Fig. 1 . The system's main components include three cylinders, an injection pump, a core holder, a back-pressure regulator, and a produced fluid collection container. The cylinders and the core holder were housed inside an oven to maintain the system temperature at 50°C or 70°C. During the test, the injection rate was set to 2 cm³/min. To inject a specific fluid, the valves for the other cylinders were closed, and the valve for the desired fluid was opened. Water Flooding (Secondary Recovery) During water flooding, water was injected at a constant rate of 3 cm³/min until oil production from the sand pack model became negligible (less than 1 cm³). The produced oil and water were collected in graduated tubes, and their volumes were recorded. Furthermore, water breakthrough times were observed. At the end of the water flooding process, the residual oil saturation was determined. Surfactant Flooding (Tertiary Recovery) The sand pack model was heated to the reservoir temperature of 50°C or 70°C. Upon reaching the desired temperature, the surfactant solution was injected at a rate of 3 cm³/min, followed by saline water injection until oil production ceased. The tests were conducted at an optimum surfactant concentration of 0.25% and salinities of 50 × 103, 100 × 103, and 200 × 103 ppm. For each surfactant slug size, the produced oil and water were collected in graduated cylinders and their volumes were recorded. Water breakthrough times were also measured for the different slug sizes. The properties of the reservoir model are provided in Table 1 . Table 1 Properties of Reservoir Model Property Value Reservoir type Diameter (mm) Length (mm) Surface (cm²) Bulk volume (cc) PV known (cc) ρ fluid (g/cc) Porosity (%) Sandstone 50.00 300.00 19.63 589.28 150.00 1.00 25.00 3. Results and Discussion 3.1 Investigation of Phase Behavior and Solubilization Parameters The most crucial factor in determining the success of chemical flooding is the phase behavior of the mixture of brine, crude oil, and surfactant. In these surfactant systems, achieving ultralow interfacial tension (IFT) is critical, as it is effective for studying the phase behavior of microemulsions, particularly in regions of high solubilization. The phase behavior of the system is primarily governed by surfactant concentration, crude oil properties, and brine salinity. Additionally, the effect of high temperature under typical reservoir conditions is a critical parameter. Therefore, the main aim of this study is to determine the combined effects of salinity and temperature on the phase behavior of the surfactant-brine-crude oil system for enhanced oil recovery (EOR) applications. The phase behavior was investigated to determine the effect of increasing salinity and temperature on the stability of the surfactant-brine-crude oil emulsion. The volumes of solubilized water and oil in the microemulsion system were used to determine the solubilization parameters for the Winsor Type III microemulsion. The oil solubilization parameter (Vo/Vs) increased with salinity, while the water solubilization parameter (Vw/Vs) decreased. At low salinity, the majority of the surfactant and co-surfactant resided in the aqueous phase, with only a trace amount solubilized in the oil phase. At high salinity, only a small amount of surfactant was soluble in the aqueous phase, with the majority residing at the interface. As salinity increased, the oil solubilization parameter increased, while the water solubilization parameter decreased. The salinity at which these two values became equal is known as the optimal salinity. The optimal salinity depends on the crude oil type, the surfactant-to-co-surfactant ratio, and temperature. For the EHWO14 system, Fig. 2 shows the interfacial tension (IFT) and solubilization parameters as functions of salinity. Figure 3 depicts the same relationships for a blend of EHWO14 with EABS14 and isopropanol as a co-surfactant (denoted as EHWO14 + EABS14+Cs). Furthermore, Fig. 4 shows the interfacial tension (IFT) and solubilization parameters as functions of salinity for the EHWONa system. The experimental results indicate that salinity increases solubilization parameters up to a maximum value, beyond which they decrease. In this study, the optimal salinity was determined to be 100 × 10³ ppm. At this optimum salinity, the middle-phase microemulsion solubilizes equal volumes of oil and water. After exceeding the optimal salinity, a further increase in salt concentration to 200 × 10³ ppm decreased the water solubilization parameter. Concurrently, the microemulsion system transitioned from Winsor type I to Winsor type III, and finally to Winsor type II as salinity increased. These phase transitions can be explained by the interaction of inner droplets and interfacial bending stress. Specifically, increasing salt concentration attracts water molecules to solvate the ions. This reduces the number of water molecules available to hydrate the hydrophilic head groups of the surfactant, increasing the attraction between the head groups and reducing the effective cross-sectional area of the surfactant's hydrophilic head. Consequently, the natural curvature of the interface changes, promoting a transition toward a water-in-oil (Winsor II) microemulsion. The curvature of the interfacial film transitions from positive, to zero, to negative, corresponding to the microemulsion phase transition from oil-in-water (O/W, Winsor I), to bi-continuous (Winsor III), to water-in-oil (W/O, Winsor II). Consequently, with increasing salinity, the microemulsion system undergoes a transition where the surfactant-rich phase shifts from the lower (O/W) to the middle (bi-continuous) to the upper (W/O) phase. Accordingly, the oil solubilization parameter (Vo/Vs) increases with salinity, while the water solubilization parameter (Vw/Vs) decreases [ 37 – 42 ]. 3.2 Phase Diagram of the Micro Emulsion System Pseudo-ternary diagrams were constructed with brine, crude oil, and a surfactant/co-surfactant mixture (S + Cs) as the three components. These diagrams were established for various surfactants to determine the composition of the microemulsion phase. Furthermore, formulating microemulsions with a low surfactant concentration is essential for cost reduction. Figure 5 presents the corresponding pseudo-ternary diagram for the surfactant EHWO14, formation water, and crude oil, with the microemulsion region indicated by the shaded area. The pseudo-ternary diagram in Fig. 10 , which features the surfactant blend (EHWO14 + EABS14+Cs), formation water, and crude oil, shows a larger microemulsion region than those of the individual surfactants (Figs. 5 and 6 ). Isopropanol, used as a co-surfactant, increases the solubility of surfactant molecules in the oil phase and enhances microemulsion stability. As shown in Fig. 7 , the microemulsion region was more stable for the anionic surfactant (EHWONa) than for the individual nonionic surfactant or their blends. Figure 8 shows the phase behavior of EHWO14, its derivatives (EHWO14 + EABS14+Cs), and EHWONa at optimal salinity and different temperatures. 3.3 Microscopic Investigation of the Micro Emulsion Phase Volume The experiments were carried out using EHWO14 at 25°C in formation water with total dissolved solids (TDS) concentrations of 50 × 10³, 100 × 10³, and 200 × 10³ ppm. A middle-phase microemulsion formed at a 1:1 oil-to-water ratio, as confirmed by optical microscopy. However, this microemulsion gradually separated at salinities of 50 × 10³ and 200 × 10³ ppm when the temperature was increased from 25°C to 70°C. The microemulsion remained stable at a salinity of 100 × 10³ ppm across all three temperatures. As the temperature increased, the oil viscosity decreased, leading to the agglomeration of oil droplets in the upper phase. The blend (EHWO14 + EABS14+Cs) was used to prepare the microemulsions at 25°C and three different salinities. After settling, the largest microemulsion region was observed at the salinity of 100 × 10³ ppm. A microemulsion formed at salinities of 50 × 10³ and 100 × 10³ ppm, but the region decreased at 200 × 10³ ppm. This behavior is likely due to achieving a minimum interfacial tension of 2 × 10⁻² mN/m. As the temperature increased, the microemulsion region gradually decreased. However, analysis of microscopic data for the anionic surfactant EHWONa at the optimal salinity of 100 × 10³ ppm showed that the microemulsion region was largest and most stable at 50°C. Microemulsions are highly sensitive to elevated temperatures; this thermal instability must be balanced during the formulation of a surfactant flooding process [ 43 – 48 ]. 3.4 Factors Effect on Phase Behavior Molecular Structure Molecular structure is one of the most crucial factors affecting surfactant performance. In this study, modifications to the molecular structure played a vital role in phase behavior. The data show that anionic surfactants are more efficient than nonionic surfactants when used individually, while surfactant blends produced the most stable microemulsions. Surfactant Concentration Surfactant concentration was maintained at the critical micelle concentration (CMC), as this value represents the point of maximum efficiency. However, for the flooding process, the surfactant was injected at a concentration slightly above the CMC to compensate for losses due to adsorption onto the rock surface. Cosolvents Co-solvents, like isopropanol, increase microemulsion stability by enhancing the solubility of surfactant molecules in the oil phase. Salinity Salinity significantly influenced the phase behavior, with an optimal salinity observed at 100 × 10³ ppm. Increasing the salinity raised the oil solubilization ratio while decreasing the water solubilization ratio. In distilled water, a balance exists between monolayer surfactant adsorption at the interface and micellization. Furthermore, hydrogen bond formation induces significant coiling of the ethylene oxide groups, which increases the minimum area per molecule (A min ) and decreases the maximum surface concentration (Γ max ). Conversely, in formation water, the high salt concentration disrupts hydrogen bonding, which reduces A min and increases Γ max . This mechanism is critical for enhanced oil recovery (EOR), as the increased oil solubilization at the interface improves the overall efficiency of the process. Temperature Temperature is a critical parameter for surfactant-based enhanced oil recovery due to its significant influence on surfactant molecules at the interface and within the bulk brine phase. Figure 8 shows the effect of temperature on microemulsion phase behavior. As temperature increases, thermal agitation reduces the number of surfactant molecules at the interface, thereby increasing the minimum area per molecule (Amin). However, at specific temperatures, the formation of thermodynamically stable microemulsions can improve oil displacement and increase the EOR efficiency. While the volume fraction of the aqueous phase remains largely constant with increasing temperature, the volume of the middle phase decreases considerably as excess oil is released. This reduction continues up to a specific temperature, beyond which the middle-phase volume stabilizes [ 36 ]. There are also factors such as crude oil type and water-oil ratio. 3.5 Contact Angle and Wettability Alteration The contact angle of crude oil is influenced by surface charge density. Figure 9 illustrates the contact angle for crude oil on clean, loose sandstone samples (Arenite with mineralized SiO₂) treated with the surfactant EHWO14 and its blend formulations (EHWO14 + EABS14+Cs). According to Table 2 , the contact angle of the untreated oil droplet was highly obtuse (159°), indicating an oil-wet rock phase. Treatment with surfactant formulations shifted the wettability to a water-wet state. Surfactants facilitate this change by reducing the interfacial tension (IFT) and contact angle, thereby lowering the adhesion work required to separate oil droplets from the rock surface and mobilize them. This reduction in adhesion work is essential for enhancing oil recovery. The temporal evolution of the contact angle is termed the dynamic contact angle. Figure 9 shows this dynamic behavior, demonstrating that the presence of surfactant in the flooding formulations consistently reduces the contact angle over time. When surfactant adsorbs onto the oil droplet, its stability decreases, promoting rupture. In this study, surfactant adsorption at the oil-water interface formed a monolayer that rendered the oil droplet surface more hydrophilic. This promotes the formation of low-viscosity oil-in-water emulsions, thereby improving oil displacement and enhancing EOR efficiency [ 49 , 50 ]. Table 2 Physical Terms of EHWO14 and its Blends Surfactant Designation HLB Static IFT (mN/m) Dynamic IFT (mN/m) Static Contact Angle(Ө) Dynamic Contact Angle(Ө) 1- Ethoxylated Hydrolyzed Waste Cooking Oil (eo = 14) EHWO14 14.6 4×10 − 2 1×10 − 2 31 27 2- Ethoxylated Hydrolyzed Waste Cooking Oil (eo = 14) + alkyl Benzene sulfonate (eo = 14) EHWO14 +EABS14 14.6 1×10 − 1 8×10 − 2 40 35 3- Ethoxylated Hydrolyzed Waste Cooking Oil (eo = 14) + Ethoxylated alkyl Benzene sulfonate (eo = 14) + Co Surfactants EHWO14 +EABS14 + Cs 12.4 1×10 − 2 1×10 − 3 25 22 3.6 Work Adhesion Wettability is an essential property in many surfactant applications. The contact angle (θ) of a liquid on a solid surface is influenced by the reduction in surface tension induced by a surfactant. This angle is governed by the liquid's surface tension, the solid's surface energy, and the solid-liquid interfacial tension. Furthermore, the arrangement and alignment of surfactant molecules at the solid-liquid interface directly affect the work of adhesion (Wa). The extent of wetting can be described by the difference between the work of adhesion (Wa) and the work of cohesion (Wc). Both the work of adhesion and the contact angle are dependent on the composition and surface tension properties of the solid and liquid. The residual oil saturation decreases as the contact angle at the fluid/rock/oil interface increases. The surfactant molecules present in the flooding solution penetrate this interface and adsorb onto the rock surface. The contact angle increases towards the oil but decreases towards the surfactant liquid/rock. This change caused the oil to ripple and detach from the sandstone surface, forming an oil-in-water (O/W) emulsion. As a result, the amount of recovered oil increased. The following mechanism details the process of oil recovery by surfactant. The adsorption of surfactant molecules onto the rock surface is a physical process. Wettability alteration involves several steps: Initial State: Oil droplets initially wet the rock surface, characterized by a high contact angle (θ >> 90°), indicating a strongly oil-wet condition. Pre-CMC Surfactant Addition: Surfactant is added at a concentration below its Critical Micelle Concentration (CMC). At this monomeric phase, adsorption is minimal. Although the contact angle decreases slightly, the system remains oil-wet (θ > 90°). At the CMC: When the surfactant concentration reaches the CMC, a monolayer of molecules penetrates the oil-rock interface, significantly reducing the interfacial tension (IFT). Simultaneously, the oil droplets and formation water develop a stable electrical double layer. This causes the contact angle to decrease below 90° (θ < 90°), indicating a shift in wettability. Post-CMC Dynamics: Over time, the dynamic IFT shows a further reduction, and the contact angle decreases even more (θ << 90°). At this point, the sand rock surface becomes nearly water-wet, covered by a complete monolayer of adsorbed surfactant. Final Recovery: Ultimately, the oil viscosity is reduced, achieving complete wettability alteration and forming an oil-in-water (O/W) emulsion. The recovery factor reaches its maximum value through the action of a nonionic surfactant blend with a cosurfactant (EHWO14 + EABS14+Cs). This mechanism was discussed in previous work [ 51 ]. The work of adhesion was calculated using the Young-Dupre equation (Eq. 5) and the results are listed in Table 3 . Table 3 Work Adhesion and Surface Free Energy of EHWO14 and its Blend Surfactant Static ST (mN/m) Static IFT (mN/m) Static Contact Angle(Ө) Work Adhesion, Wa (mJ/m 2 ) Surface Free Energy, γ S (mJ/m 2 ) Spreading coefficient,Ws Blank 67 19.5 155 6×10 − 3 -2×10 − 2 -0.127 EHWO14 28.5 4×10 − 2 31 5×10 − 2 1×10 − 2 -4×10 − 3 EHWO14 + EABS14 25.2 1×10 − 1 40 4×10 − 2 4×10 − 3 -5×10 − 3 EHWO14 + EABS14+Cs 21.8 1×10 − 2 25 4×10 − 2 7×10 − 2 -2×10 − 3 Wa = γ L (cos Ө + 1) (5) The Young-Dupre equation relates the work of adhesion to the interfacial tension (IFT) of the liquid (γ L ) and the contact angle (θ). The difference between the work of adhesion of the solution to the surface (Wa) and the work of cohesion (Wc) provides information about the wettability of the process. According to the data in Table 3 , the work of adhesion for the blend (EHWO14 + EABS14+Cs) was 4 × 10⁻² mJ/m², which is lower than that of the individual surfactant EHWO14 (5 × 10⁻¹ mJ/m²). This lower Wa value for the blend corresponds to its lower interfacial tension (IFT), indicating a positive correlation between work of adhesion and IFT. 3.7 Surface Charge Energy The surface free energy, which determines the wetting and adhesion characteristics of a material, can be calculated using a contact angle measurement method. The specific calculation is given by Eq. 6. γ L cos Ө = Ө γ S γ SL (6) Where γ L is the surface tension of the liquid (mN/m), γ S is the surface free energy of the rock, and γ SL is the interfacial tension of the used system. By rearranging Eq. 6. γ S = γ L cos Ө / Ө γ SL (7) Based on the data in Table 3 , the surface free energy of the surfactant blend (EHWO14 + EABS14+Cs) was 7 × 10⁻² mJ/m². This value is lower than that of the individual surfactant EHWO14 (1 × 10⁻¹ mJ/m²). The lower surface free energy observed for the blend can be attributed to its correspondingly lower interfacial tension (IFT) compared to the individual surfactants. 3.8 Spreading Coefficient of Surfactant on the Rock Surface The spreading coefficient is a mathematical expression that describes how a liquid spreads on a solid surface, based on the difference between the work of adhesion and cohesion. For this study, the spreading coefficient of surfactant molecules on sandstone was determined using Eq. 8. Ws = γ L (cos Ө − 1) (8) Where Ws is the spreading coefficient, γL is the IFT, and Ө is the contact angle. The spreading coefficient can be used as a wettability index because it increases with the wettability of oil-covered rock. The blend EHWO14 + EABS14+Cs has a spreading coefficient of -2 × 10⁻³, which is less negative than the value of -4 × 10⁻² for the individual surfactant EHWO14. This indicates a higher wettability for the blend [ 52 ]. According to the data in Table 3 , the negative spreading coefficient indicates that the rock is more water-wet than oil-wet, which is favorable for enhanced oil recovery (EOR). The coefficient is calculated using the equation Ws = γ L (cos θ − 1), which shows its dependence on both interfacial tension (IFT) and contact angle. A negative spreading coefficient, often achieved by reducing the IFT, is desirable as it promotes the release of oil droplets from the rock surface. Additionally, isopropanol acts as a co-surfactant and influences the spreading coefficient by reducing the IFT. For the blend containing isopropanol, the spreading coefficient has the highest value) among the samples tested. 3.9 Enhanced Oil Recovery Factor of the Surfactant Flooding The key to surfactant flooding in enhanced oil recovery (EOR) is designing a surfactant slug with an optimal concentration. This process is influenced by various parameters, including temperature, critical micelle concentration (CMC), adsorption characteristics on the sand-packed model, interfacial tension, contact angle, and wettability alteration at the core-formation water interface. Flooding experiments were conducted for EHWO14 and its blends, both with and without the co-surfactant isopropanol. The experiments were performed at slightly above CMC concentrations, using different temperatures (50°C, 70°C) and salinities (50 × 10³, 100 × 10³, 200 × 10³ ppm) on a sand-packed model. The co-surfactant reduces the interfacial tension (IFT), which improves microemulsion stability by enhancing the solubility of surfactant molecules in the oil phase. This mechanism ultimately leads to a higher recovery factor (RF). As shown in Table 4 , which presents the cumulative oil recovery percentages for EHWO14 and its blends, the maximum RF of 79% was achieved by the blend EHWO14 + EABS14+Cs at a salinity of 100 × 10³ ppm and a temperature of 50°C. The action of surfactant molecules at the interface creates a complete adsorbed layer and a stable electric double layer. This leads to a reduction in interfacial tension (IFT) and, consequently, an increase in the oil recovery factor. To characterize this behavior, the solubilization parameters and phase behavior of the prepared surfactants were determined at different temperatures and salinities. The best performance, as shown in Figs. 10 and 11 , was achieved by the surfactants and their blends at a salinity of 100 × 10³ ppm and a temperature of 50°C. These results are attributed to the specific properties and behavior of the surfactants. Furthermore, maximum oil solubilization occurred at the optimal salinity and at concentrations above the critical micelle concentration (CMC). Conversely, recovery is low at concentrations both below and above the CMC. At concentrations significantly above the CMC, increased surfactant adsorption can form multilayers, leading to water-in-oil (W/O) emulsion that impedes oil recovery. The mechanism by which concentration affects the recovery factor was discussed in previous work [ 51 ]. Figure 12 illustrates a novel mechanism proposed in this study, explaining how both traditional (individual) surfactants and their blends affect the recovery factor (RF). For surfactant blends, the molecules form well-organized adsorbed monolayers at the interface. This configuration promotes efficient stripping of oil droplets from the pore surfaces, forming an oil-in-water (O/W) emulsion. This emulsion has lower viscosity, thereby increasing the recovery factor. In contrast, traditional surfactants initially form a successful adsorbed monolayer. However, they tend to subsequently develop a multi-layer or double-layer structure. This leads to an inversion of the emulsion type from O/W to water-in-oil (W/O), which increases viscosity and ultimately decreases the recovery factor. Table 4 Cumulative Oil Recovery Percent at Different Salinities and Different Temperatures for EHWO14 and its Blends Subject Salinity (ppm) Temperature (°C) Sec. Recovery Ter. Recovery Residual oil Total Recovery CC % CC % CC CC % EHWO14 50 ×10³ 50 58.00 48.33 21.75 35.08 62.00 79.75 66.45 EHWO14 100 ×10³ 50 55.00 45.83 33.12 50.69 61.53 88.12 71.00 EHWO14 100 ×10³ 70 54.19 47.12 26.00 42.75 60.81 80.19 66.82 EHWO14 200 ×10³ 70 53.00 44.16 25.00 37.31 67.00 78 65.00 EABS14 + EHWO14 200 ×10³ 50 53.00 44.16 34.50 50.73 68.00 87.5 72.91 EABS14 + EHWO14+Cs 100 ×10³ 50 56.00 46.66 34.00 53.12 64.00 90 79.00 EHWONa 100 ×10³ 50 56.00 48.69 32.00 54.23 59.00 88 73.33 EHWONa 100 ×10³ 70 56.50 47.08 27.00 42.51 63.50 83.5 69.58 EHWONa+EHWO14 100 ×10³ 50 58.50 48.75 29.00 47.15 61.50 87.5 72.91 EHWONa+EHWO14 100 ×10³ 70 56.00 46.66 19.00 29.68 64.00 75 62.50 4. Conclusions This study introduced various green surfactants—including nonionic, anionic, and blended types based on aliphatic and aromatic moieties prepared from waste cooking oil—for improving crude oil recovery. The main conclusions are as follows: At 50°C and a salinity of 100 × 10³ ppm, the EHWO14 + EABS14+Cs blend reduced the interfacial tension (IFT) to 1 × 10⁻³ mN/m. This decrease was more significant than those achieved by EHWO14 alone (1 × 10⁻² mN/m) and the EHWO14 + EABS14 blend (8 × 10⁻² mN/m). At 50°C and a salinity of 100 × 10³ ppm, the EHWO14 + EABS14+Cs blend reduced the contact angle from 159° to 22°. In contrast, the contact angles for EHWO14 and the EHWO14 + EABS14 blend were 27° and 35°, respectively. The phase behavior and solubilization parameters were investigated for all prepared surfactants at different temperatures (25, 50, and 70°C) and salinities (50×10³, 100×10³, and 200 × 10³ ppm). The minimum interfacial tension was achieved at the optimal salinity of 100 × 10³ ppm. The microscopy study demonstrated that the anionic surfactant enhanced oil-in-water emulsion formation more effectively than the individual nonionic surfactants. However, the nonionic surfactant blends were found to be preferable as they produced more stable emulsions. Data for the work of adhesion (Wa), surface free energy (γs), and spreading coefficient (Ws) indicate that the surfactant blends minimize interfacial tension, increase oil solubility, separate oil droplets from the rock surface, and mobilize the oil as an oil-in-water emulsion. The total oil recovery at 50°C and a salinity of 100 × 10³ ppm was 71% for EHWO14, 72.91% for the EHWO14 + EABS14 blend, and 69.58% for EHWONa. The highest crude oil recovery (79%) was achieved by the EHWO14 + EABS14+Cs blend at 50°C and a salinity of 100 × 10³ ppm. These results demonstrate the potential of these waste-based surfactants for enhanced oil recovery applications. Declarations Competing Interests The authors have no relevant financial or non-financial interests to disclose. Conflicts of interest : There are no conflicts of interest to declare. Funding The authors declare that no funds, grants, or other support were received during the preparation of this manuscript. Author Contribution All authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by prof. Dr. Ahmed Mohamed El-Sabagh, prof. Dr. Fatma Hosny Abdel-Salam, and Dr. Asmaa Mohamed. The first draft of the manuscript was written by Dr. Asmaa Mohamed, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript. Acknowledgement The authors acknowledge the Egyptian Academy of Scientific Research and Technology (ASRT) for sharing Project 56/2015 (Construction of a semi-pilot plant for enhanced oil recovery (EOR) by unconventional methods) (2015–2018) with the Egyptian Petroleum Research Institute (EPRI). The authors should also thank all members of the EPRI-EOR/IOR Project. 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Abdel-Salam","email":"","orcid":"","institution":"Al Azhar University","correspondingAuthor":false,"prefix":"","firstName":"Fatma","middleName":"H.","lastName":"Abdel-Salam","suffix":""},{"id":614653540,"identity":"458bfafc-23b0-4614-a311-25f6fd45be2f","order_by":2,"name":"Asmaa Mohamed","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA3ElEQVRIiWNgGAWjYDADfobDB4CUhAzxWiQbjyWAtPAQr8Xg8BkDEE1YC/+002kPfvyxyTc4dubzqxs1FjwM7IePbsCnReJ27nbD3rY0y5lnzm6zzjkGdBhPWtoNvNbczt0mwdtw2IDvxtltxjlsQC0SPGZ4tcgDtUj++fPfgOH+m2fGOf+I0GIA1CLNw3bAQODAGebHuW1EaDEEaZFtSzaQbDhmxpzbJ8HDRsgvciCHvfljZwCMysefc77VyfGzHz6G3/tIgE0CTBKrHASYP5CiehSMglEwCkYOAADM3kxRqERCKQAAAABJRU5ErkJggg==","orcid":"","institution":"Egyptian Petroleum Research Institute","correspondingAuthor":true,"prefix":"","firstName":"Asmaa","middleName":"","lastName":"Mohamed","suffix":""}],"badges":[],"createdAt":"2026-01-13 20:38:12","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-8595521/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-8595521/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":105815688,"identity":"6841be4d-234a-4119-bb74-fa53dd6a0d58","added_by":"auto","created_at":"2026-03-31 12:21:15","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":600402,"visible":true,"origin":"","legend":"\u003cp\u003eSchematic Setup of Chemical Flooding Process\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/c164fbbc87cd96a87b66722d.png"},{"id":105904585,"identity":"48da361f-eff1-4be5-a9a2-71e1a446f659","added_by":"auto","created_at":"2026-04-01 10:09:43","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":37157,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Interfacial Tension vs. Salinity; (b) Solubilization Parameters vs. Salinity for EHWO14\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/d4c0027a5240239bb1836f48.png"},{"id":105904465,"identity":"fce94054-04cf-4e23-88ef-83e7a6720756","added_by":"auto","created_at":"2026-04-01 10:08:48","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":61122,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Interfacial Tension vs. Salinity; (b) Solubilization Parameters vs. Salinity for EHWO14+EABS14+Cs\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/4a1f395ba8d9649bd4f0607e.png"},{"id":105904567,"identity":"69c9d613-4155-4ba4-ab59-f7e1b3036a80","added_by":"auto","created_at":"2026-04-01 10:09:34","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":35719,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Interfacial Tension vs. Salinity; (b) Solubilization Parameters vs. Salinity for EHWONa\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/85c6aaaf77e534124710f4c7.png"},{"id":105904959,"identity":"56adbb45-ca35-40de-a87a-dd921521ddf4","added_by":"auto","created_at":"2026-04-01 10:11:13","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":65446,"visible":true,"origin":"","legend":"\u003cp\u003eTernary Phase Diagram of Oil-Brine- Surfactant (EHWO14) System\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/2f58bcf7848218ac6b76dfb2.png"},{"id":105904216,"identity":"72a0baf5-15f3-4e14-83fe-b27de0daa681","added_by":"auto","created_at":"2026-04-01 10:06:23","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":74157,"visible":true,"origin":"","legend":"\u003cp\u003eTernary Phase Diagram of Oil-Brine- Surfactant Blend (EHWO14+EABS14+Cs) System\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/18158a2ce6ae55b26c7bbb89.png"},{"id":105815690,"identity":"39036d56-944b-46d3-9352-29e82029c903","added_by":"auto","created_at":"2026-03-31 12:21:15","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":72728,"visible":true,"origin":"","legend":"\u003cp\u003eTernary Phase Diagram of Oil-Brine- Surfactant (EHWONa) System\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/0eb582d314c06b751d100ce1.png"},{"id":105904824,"identity":"b1e9ac76-2f93-4493-9d53-fb4b24351eca","added_by":"auto","created_at":"2026-04-01 10:10:38","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":209229,"visible":true,"origin":"","legend":"\u003cp\u003ePhase Behavior of EHWO14 and Its Derivatives at Optimal Salinity and Different Temperatures\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/9f4e21c4487877d2febf5d37.png"},{"id":106092945,"identity":"23f4b38d-8487-45c9-bfeb-7d03aef8f699","added_by":"auto","created_at":"2026-04-03 11:31:14","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":71044,"visible":true,"origin":"","legend":"\u003cp\u003e(a) Contact Angles vs. Time; (b) IFT vs. Time for EHWO14 and its Blend (EHWO14+EABS14+Cs) at 50 \u003csup\u003e◦\u003c/sup\u003eC\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/64d7f8354465ee06da16236a.png"},{"id":105904448,"identity":"bbe8c43d-dc6c-44a9-9903-aa3820061cfb","added_by":"auto","created_at":"2026-04-01 10:08:40","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":79710,"visible":true,"origin":"","legend":"\u003cp\u003eSecondary Recovery for EHWO14, EHWO14 + EABS14 + Cs, and EHWONa at 50 \u003csup\u003e◦\u003c/sup\u003eC and Salinity 100×10\u003csup\u003e3 \u003c/sup\u003eppm\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/9c7c0a6993d467e82010cdc1.png"},{"id":105815691,"identity":"9e1c240b-16df-4d01-bcce-bc02077537b5","added_by":"auto","created_at":"2026-03-31 12:21:15","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":91406,"visible":true,"origin":"","legend":"\u003cp\u003eTertiary Recovery for EHWO14, EHWO14 + EABS14 + Cs, and EHWONa at 50 \u003csup\u003e◦\u003c/sup\u003eC and Salinity 100 × 10\u003csup\u003e3 \u003c/sup\u003eppm\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/8de3efbaac10bd8c26b2982e.png"},{"id":105815693,"identity":"d89d52a9-8ec1-458a-8ffa-9c45ec1dad2f","added_by":"auto","created_at":"2026-03-31 12:21:15","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":324560,"visible":true,"origin":"","legend":"\u003cp\u003eMolecular Mechanism of the Blends performance and Traditional Surfactants in EOR\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/4732000fd8a8a13dc035ba98.png"},{"id":106401939,"identity":"7af8d106-0b1e-4ef6-95db-00990069b328","added_by":"auto","created_at":"2026-04-08 09:10:18","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":3094294,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/b6cf3ff2-6ffc-44ab-999f-d4ecf73d1727.pdf"},{"id":105815685,"identity":"3a96a0b9-cce6-45d5-9619-6a6a1bedd6f8","added_by":"auto","created_at":"2026-03-31 12:21:15","extension":"docx","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":296472,"visible":true,"origin":"","legend":"","description":"","filename":"GraphicalAbstract.docx","url":"https://assets-eu.researchsquare.com/files/rs-8595521/v1/43ba552ec163a1faf9435849.docx"}],"financialInterests":"No competing interests reported.","formattedTitle":"Conversion of Waste Cooking Oil to Environmentally Acceptable Surfactants for Enhanced Oil Recovery","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThe oil and gas sectors are looking for improved oil recovery strategies to increase the recovery of oil from reservoirs. Injecting chemical slugs into oil reservoirs is a well-established EOR method [\u003cspan additionalcitationids=\"CR2 CR3\" citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e]. The most common variants of this method involve injecting slugs containing surfactant, alkaline surfactant, or alkaline-surfactant-polymer (ASP) [\u003cspan additionalcitationids=\"CR6 CR7 CR8\" citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e]. By adjusting the injected fluid's parameters, each additive in the chemical slug enhances the EOR mechanisms, such as interfacial tension (IFT) reduction, wettability alteration, and mobility ratio control [\u003cspan additionalcitationids=\"CR11 CR12\" citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e]. Because microemulsions can significantly reduce the IFT between water and oil, they play crucial role in EOR applications. In reservoir rock pores, microemulsions can effectively mobilize trapped oil by overcoming capillary forces. During microemulsion flooding, surfactants and co-surfactants are injected to form a middle-phase microemulsion, achieving ultra-low interfacial tension (IFT) between 10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e and 10\u003csup\u003e\u0026minus;\u0026thinsp;4\u003c/sup\u003e mNm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e. Microemulsions significantly enhance oil recovery due to their large specific surface area, smaller droplet size, low IFT, unique solubility, and penetration properties. The microemulsion evaluation methodology comprises core flooding experiments, stability analysis, and interfacial tension measurements. There are four types of microemulsions according to the Winsor classification: Type I (oil-in-water, O/W), Type II (water-in-oil, W/O), Type III (bi continuous middle phase), and Type IV (single-phase isotropic solution). In Winsor Type I systems, oil becomes solubilized in the aqueous phase through encapsulation by surfactant tails forming micellar structures. Winsor Type II systems consist of reverse micelles that solubilize water within the continuous oil phase. Winsor Type III systems exhibit a bi continuous middle phase where surfactant molecules form interconnected networks between oil and water domains. In this bi continuous phase, both oil and water become molecularly dispersed. Winsor Type IV occurs when sufficient surfactants completely solubilize all water and oil components into a single isotropic solution. Compared to Winsor Type I and II, Winsor Type III and Type IV microemulsions demonstrate superior interfacial tension (IFT) reduction between oil and water phases [\u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e]. Low interfacial tension (IFT) indicates high mutual solubility between oil and water phases. For effective EOR development, three critical factors must be addressed: accurate characterization of reservoir rock wettability, optimal control of surfactant adsorption, and efficient IFT reduction at oil-water interfaces. Surfactant chemistry plays a pivotal role in achieving these interfacial modifications by controlling molecular interactions at fluid-fluid and fluid-rock interfaces. Surfactant molecules are essential for controlling IFT in enhanced oil recovery applications. Surfactant molecules modify interfacial molecular interactions through adsorption at liquid-liquid interfaces, reducing repulsive forces and stabilizing the system by minimizing interfacial energy. The aqueous solution contains surfactant monomers that adsorb at interfaces, forming a monolayer which reduces both surface and interfacial tension. At specific concentrations, surfactant monomers form a closed aggregate (micelle), with the hydrophobic tails preserved from water and the hydrophilic heads facing it. This transition point is defined as the critical micelle concentration (CMC), a key surfactant property [\u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e]. Surfactant injection has been successfully implemented in oilfield applications. Optimizing both concentration and selecting appropriate surfactants as key components of chemical slugs are critical for effectively mobilizing residual oil trapped in reservoir pore spaces. The surfactants are typically introduced into the injected water to achieve significant interfacial tension reduction between oil and water phases. Since surfactant performance and stability vary significantly with reservoir conditions, comprehensive EOR laboratory testing is essential to quantify surfactant efficiency prior to field implementation. The application of bio-based surfactants has gained significant attention in recent years. Researchers are increasingly investigating novel natural sources for surfactant production, motivated by their cost-effectiveness, abundant availability, and environmental sustainability [\u003cspan additionalcitationids=\"CR19 CR20 CR21 CR22\" citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e]. For example, a castor oil-derived surfactant demonstrated exceptional performance by achieving ultra-low interfacial tension and effectively altering sandstone wettability from oil-wet to strongly water-we [\u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e]. The surfactants have stable foam and emulsion properties [\u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e]. To overcome the drawbacks of chemical surfactants, such as their high cost and environmental incompatibility, research into bio-based surfactants is ongoing. From both scientific and commercial perspectives, biosurfactants offer benefits such as sustainability and environmental friendliness [\u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e]. Additional benefits of natural surfactants include low toxicity, high biodegradability, and greater accuracy and efficacy at high pH and temperature [\u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e]. Various studies on the use of waste materials in EOR were reviewed, including those on environmentally safe potassium-doped graphene oxide particles made from oak fruit waste. These raw materials are abundant, cost-effective, biocompatible, biodegradable, and readily accessible. Interfacial tension, critical micelle concentration, and zeta potential were measured to assess the stability of particles treated with different surfactants. Adsorption experiments subsequently quantified surfactant loss during the flooding process [\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e]. A further investigation found that reduced graphene oxide, synthesized using waste plastic as a carbon source, enhanced the EOR process. These materials exhibit superior electrical, mechanical, and thermal properties because the synthesized graphene has a larger surface area than conventional metal oxide nanoparticles, resulting in higher surface activity. Converting solid waste into valuable carbon-based nanomaterials is a vital strategy for solid waste management [\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e]. Additionally, red onion skin, an agricultural waste biomass, was chosen as a natural recovery agent. This agricultural waste is a crucial source of quercetin, flavones, anthocyanins, and polyphenolics. Red onion skin was treated with glutaraldehyde in an aqueous sodium hydroxide solution and its efficacy was assessed in a sandstone core [\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e]. Another study was conducted to investigate the interactions of a biopolymer (animal glue) and a surfactant (lauryl ether sulfate) with hydrolyzed polyacrylamide. Several laboratory floods using steam, surfactant, biopolymer, and polymer were conducted individually and in combination on a semi-pilot model [\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e]. Many studies offer a critical evaluation of various green innovations for enhanced oil recovery, including organic materials injection, nanotechnology application, solar energy integration, microbial processes, water alternating gas, foam injection, and nanofluid injection, all contributing to a cleaner environment [\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e]. Researchers focus on the various advantages of green nanocomposites in EOR, primarily their safety for living things. As they are derived from plants or other safe industrial resources, these nanocomposites represent a highly attractive alternative EOR technique [\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e]. In another study, zinc oxide nanoparticles, which can prevent asphaltene deposition, reduce interfacial tension, and alter wettability, were combined with green nanocomposites in porous media for enhanced oil recovery [\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e]. Waste cooking oil (WCO) is a non-edible oil produced in large amounts. Its careless disposal may have a detrimental effect on humanity and the environment [\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e]. In this work, a natural bio-based surfactant will be prepared from waste cooking oil, a renewable source. The study's objectives include synthesizing this surfactant and evaluating its performance through critical micelle concentration (CMC) measurements, water-oil interfacial tension (IFT) analysis, wettability tests, ideal salinity determination, phase behavior observation, and oil recovery tests for enhanced oil recovery (EOR) applications.\u003c/p\u003e"},{"header":"2. Materials and Methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e \u003ch2\u003e2.1 Materials\u003c/h2\u003e \u003cdiv id=\"Sec4\" class=\"Section3\"\u003e \u003ch2\u003e2.1.1 Surfactants\u003c/h2\u003e \u003cp\u003eThe anionic and nonionic surfactants used in this study were prepared from waste cooking oil [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. The surfactants used in this study are: Ethoxylated Hydrolyzed Waste Oil (eo\u0026thinsp;=\u0026thinsp;9) [EHWO9], Ethoxylated Hydrolyzed Waste Oil (eo\u0026thinsp;=\u0026thinsp;14) [EHWO14], Ethoxylated Hydrolyzed Waste Oil (eo\u0026thinsp;=\u0026thinsp;23) [EHWO23], Ethoxylated Hydrolyzed Waste Oil (eo\u0026thinsp;=\u0026thinsp;46) [EHWO46], and Hydrolyzed Waste Oil sodium salt [HWONa].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec5\" class=\"Section3\"\u003e \u003ch2\u003e2.1.2 Crude oil\u003c/h2\u003e \u003cp\u003eThe crude oil used for preparing microemulsions was sourced from the West Desert, Egypt, and provided by the General Petroleum Company (GPC). The oil had an API gravity of 27\u0026deg; at 15.55\u0026deg;C and a density of 0.8983 at 15\u0026deg;C. Its composition, determined by SARA analysis, was 57 wt% saturates, 21 wt% aromatics, 15 wt% resins, and 7.63 wt% asphaltenes.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec6\" class=\"Section3\"\u003e \u003ch2\u003e2.1.3 Formation water\u003c/h2\u003e \u003cp\u003eFormation water, obtained from GPC, was used to prepare microemulsions under reservoir conditions. The water had a total dissolved solids (TDS) content of 200 \u0026times; 10\u0026sup3; ppm. This formation water was diluted with distilled water to achieve lower salinities of 50 \u0026times; 10\u0026sup3; and 100 \u0026times; 10\u0026sup3; ppm.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec7\" class=\"Section3\"\u003e \u003ch2\u003e2.1.4 The used Sand in the Sand-Packed Model\u003c/h2\u003e \u003cp\u003eSand of various sizes (12, 18, and 20 mesh, corresponding to 1.68, 1.00, and 0.841 mm, respectively) was used to pack the model for the chemical flooding test to achieve a porosity of 25%.\u003c/p\u003e \u003c/div\u003e \u003c/div\u003e \u003cdiv id=\"Sec8\" class=\"Section2\"\u003e \u003ch2\u003e2.2 Methods\u003c/h2\u003e \u003cdiv id=\"Sec9\" class=\"Section3\"\u003e \u003ch2\u003e2.2.1 The Used Surfactant\u003c/h2\u003e \u003cp\u003ePrevious work involved preparing and characterizing surfactants extracted from waste cooking oil. The investigation included measuring surface tension, interfacial tension (IFT), estimating the critical micelle concentration (CMC), and determining thermodynamic properties [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec10\" class=\"Section3\"\u003e \u003ch2\u003e2.2.2 Preparation of Microemulsions\u003c/h2\u003e \u003cp\u003eThe procedure for microemulsion stability testing was as follows. Surfactant solutions were prepared at a concentration of 0.25% in formation water with salinities of 50 \u0026times; 10\u0026sup3; ppm, 100 \u0026times; 10\u0026sup3; ppm, and 200 \u0026times; 10\u0026sup3; ppm. Equal volumes of crude oil and surfactant solution were placed in graduated test tubes with rubber caps. The tubes were shaken by hand 60 times at a steady rate (completed within one minute) and were then allowed to settle for 24 hours. To investigate the impact of temperature, duplicate sets of tubes for each salinity were incubated at 25\u0026deg;C, 50\u0026deg;C, and 70\u0026deg;C. The entire experiment was performed in triplicate to ensure reproducibility.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e \u003ch2\u003e2.2.3 Solubilization Parameters and Relative Phase Volume\u003c/h2\u003e \u003cp\u003eThe phase behavior of the microemulsions was investigated using solubilization parameters. These parameters were calculated based on the volume of oil and water solubilized in the middle phase under ambient conditions. In the test tubes, a three-phase system was observed: an aqueous phase at the bottom, a microemulsion phase in the middle, and an oil phase at the top. This middle microemulsion phase is effective for oil recovery due to its ultra-low interfacial tension (IFT), which enables it to solubilize trapped oil from reservoir porous media. The solubilized oil volume was calculated using Eq.\u0026nbsp;1.\u003c/p\u003e \u003cp\u003eVo\u0026thinsp;=\u0026thinsp;V\u003csub\u003eoi\u003c/sub\u003e -V\u003csub\u003eof\u003c/sub\u003e (1)\u003c/p\u003e \u003cp\u003eWhere Vo represents the volume of solubilized oil in the microemulsion region, V\u003csub\u003eoi\u003c/sub\u003e represents the initial volume of the used oil, and V\u003csub\u003eof\u003c/sub\u003e represents the volume of oil in the upper phase. Similarly, the volume of water can be calculated using Eq.\u0026nbsp;2.\u003c/p\u003e \u003cp\u003eVw\u0026thinsp;=\u0026thinsp;V\u003csub\u003ewi\u003c/sub\u003e -V\u003csub\u003ewf\u003c/sub\u003e (2)\u003c/p\u003e \u003cp\u003eWhere Vw denotes the volume of solubilized water in the microemulsion region, Vwi denotes the initial volume of the used water, and Vwf denotes the volume of water in the lower phase. The solubilization values of oil and water were calculated using Eqs.\u0026nbsp;3, 4.\u003c/p\u003e \u003cp\u003eSPo\u0026thinsp;=\u0026thinsp;Vo/Vs (3)\u003c/p\u003e \u003cp\u003eSPw\u0026thinsp;=\u0026thinsp;Vw/Vs (4)\u003c/p\u003e \u003cp\u003eWhere SPo and SPw are the solubilization parameters of oil and water, and Vs is the volume of surfactant in the middle phase. The surfactant volume, Vs, is constant in the middle-phase microemulsion. On a solubilization curve, the point where the oil and water solubilization ratios are equal is crucial, as it identifies the optimal salinity. At this optimal salinity, equal amounts of oil and water are solubilized into the middle phase, forming a Type III microemulsion system.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e \u003ch2\u003e2.2.4 Phase Diagram\u003c/h2\u003e \u003cp\u003eThe solubilization method was used to construct triangular pseudo-ternary phase diagrams at room temperature (25\u0026deg;C). Surfactant (at a fixed mass), oil, and brine (pseudo-components) made up the triangle's three vertices. The experiments were set up using volumetric measurements, and the results were expressed as weight percentages.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e \u003ch2\u003e2.2.5 Oil-water IFT\u003c/h2\u003e \u003cp\u003eInterfacial tension (IFT) between crude oil and surfactant solutions was measured at critical micelle concentration (CMC) and 50\u0026deg;C. To determine the optimal salinity, IFT tests were conducted at various salinity concentrations (50 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e ppm, 100 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e ppm, and 200 \u0026times; 10\u003csup\u003e3\u003c/sup\u003e ppm).\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e \u003ch2\u003e2.2.6 Contact Angle Experiments\u003c/h2\u003e \u003cp\u003eThe wettability of the reservoir model was examined by measuring the contact angle between crude oil and sand particles. These measurements, which indicate wettability alteration, were conducted using a High-Pressure Chamber (Attention Theta model) via the sessile drop method (ASTM/ISO 19403-5). The device measured the contact angle at the interfaces between the crude oil, brine/surfactant solution, and the core surface. All measurements were conducted at a constant temperature of 50\u0026deg;C. Sandstone samples were cut into thin sections approximately 2.5 mm thick to observe the penetration and spreading of oil droplets. The sections were first cleaned with high-pressure nitrogen gas and then aged in toluene solvent for 24 hours to remove contaminants, such as fatty acids from hand contact. Finally, to achieve a hydrophobic surface, the sections were heated to 50\u0026deg;C in crude oil. Contact angle measurements were performed at the critical micelle concentration (CMC) of the surfactant solution and recorded at various time intervals. A section holder was used to suspend the rock sample in the aqueous medium, positioning it a short distance from the needle. The associated software then automatically calculated the contact angle by drawing tangent lines to the droplet at the rock surface interface.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec15\" class=\"Section3\"\u003e \u003ch2\u003e2.2.7 Emulsion Stability\u003c/h2\u003e \u003cp\u003eThe stability of emulsions prepared with the surfactant solution was tested at its critical micelle concentration (CMC), with varying salinity and co-surfactant concentrations, and at different temperatures. Test tubes containing the prepared microemulsions were placed in water baths at 50\u0026deg;C and 70\u0026deg;C to monitor their stability over time.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e \u003ch2\u003e2.2.8 Surfactants Slug Injection\u003c/h2\u003e \u003cp\u003eThe core flooding procedure was conducted as follows: the model was first saturated with water. This was followed by oil injection to establish initial oil saturation, and then brine flooding until a 98% water cut was achieved. Next, a 1 PV surfactant slug\u0026mdash;prepared at the critical micelle concentration (CMC) and the reservoir's optimum salinity\u0026mdash;was injected. Finally, brine was re-injected until the water cut reached 99%. A chemical flooding system was used to evaluate the performance of the green microemulsion. A schematic diagram of the surfactant flooding apparatus is shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. The system's main components include three cylinders, an injection pump, a core holder, a back-pressure regulator, and a produced fluid collection container. The cylinders and the core holder were housed inside an oven to maintain the system temperature at 50\u0026deg;C or 70\u0026deg;C. During the test, the injection rate was set to 2 cm\u0026sup3;/min. To inject a specific fluid, the valves for the other cylinders were closed, and the valve for the desired fluid was opened.\u003c/p\u003e \u003cp\u003e \u003cb\u003eWater Flooding (Secondary Recovery)\u003c/b\u003e \u003c/p\u003e \u003cp\u003eDuring water flooding, water was injected at a constant rate of 3 cm\u0026sup3;/min until oil production from the sand pack model became negligible (less than 1 cm\u0026sup3;). The produced oil and water were collected in graduated tubes, and their volumes were recorded. Furthermore, water breakthrough times were observed. At the end of the water flooding process, the residual oil saturation was determined.\u003c/p\u003e \u003cp\u003e \u003cb\u003eSurfactant Flooding (Tertiary Recovery)\u003c/b\u003e \u003c/p\u003e \u003cp\u003eThe sand pack model was heated to the reservoir temperature of 50\u0026deg;C or 70\u0026deg;C. Upon reaching the desired temperature, the surfactant solution was injected at a rate of 3 cm\u0026sup3;/min, followed by saline water injection until oil production ceased. The tests were conducted at an optimum surfactant concentration of 0.25% and salinities of 50 \u0026times; 103, 100 \u0026times; 103, and 200 \u0026times; 103 ppm. For each surfactant slug size, the produced oil and water were collected in graduated cylinders and their volumes were recorded. Water breakthrough times were also measured for the different slug sizes. The properties of the reservoir model are provided in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eProperties of Reservoir Model\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"2\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eProperty\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eValue\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eReservoir type\u003c/p\u003e \u003cp\u003eDiameter (mm)\u003c/p\u003e \u003cp\u003eLength (mm)\u003c/p\u003e \u003cp\u003eSurface (cm\u0026sup2;)\u003c/p\u003e \u003cp\u003eBulk volume (cc)\u003c/p\u003e \u003cp\u003ePV known (cc)\u003c/p\u003e \u003cp\u003eρ fluid (g/cc)\u003c/p\u003e \u003cp\u003ePorosity (%)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eSandstone\u003c/p\u003e \u003cp\u003e50.00\u003c/p\u003e \u003cp\u003e300.00\u003c/p\u003e \u003cp\u003e19.63\u003c/p\u003e \u003cp\u003e589.28\u003c/p\u003e \u003cp\u003e150.00\u003c/p\u003e \u003cp\u003e1.00\u003c/p\u003e \u003cp\u003e25.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003c/div\u003e"},{"header":"3. Results and Discussion","content":"\u003cdiv id=\"Sec18\" class=\"Section2\"\u003e \u003ch2\u003e3.1 Investigation of Phase Behavior and Solubilization Parameters\u003c/h2\u003e \u003cp\u003eThe most crucial factor in determining the success of chemical flooding is the phase behavior of the mixture of brine, crude oil, and surfactant. In these surfactant systems, achieving ultralow interfacial tension (IFT) is critical, as it is effective for studying the phase behavior of microemulsions, particularly in regions of high solubilization. The phase behavior of the system is primarily governed by surfactant concentration, crude oil properties, and brine salinity. Additionally, the effect of high temperature under typical reservoir conditions is a critical parameter. Therefore, the main aim of this study is to determine the combined effects of salinity and temperature on the phase behavior of the surfactant-brine-crude oil system for enhanced oil recovery (EOR) applications. The phase behavior was investigated to determine the effect of increasing salinity and temperature on the stability of the surfactant-brine-crude oil emulsion. The volumes of solubilized water and oil in the microemulsion system were used to determine the solubilization parameters for the Winsor Type III microemulsion. The oil solubilization parameter (Vo/Vs) increased with salinity, while the water solubilization parameter (Vw/Vs) decreased. At low salinity, the majority of the surfactant and co-surfactant resided in the aqueous phase, with only a trace amount solubilized in the oil phase. At high salinity, only a small amount of surfactant was soluble in the aqueous phase, with the majority residing at the interface. As salinity increased, the oil solubilization parameter increased, while the water solubilization parameter decreased. The salinity at which these two values became equal is known as the optimal salinity. The optimal salinity depends on the crude oil type, the surfactant-to-co-surfactant ratio, and temperature. For the EHWO14 system, Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e shows the interfacial tension (IFT) and solubilization parameters as functions of salinity. Figure\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e depicts the same relationships for a blend of EHWO14 with EABS14 and isopropanol as a co-surfactant (denoted as EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs). Furthermore, Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e shows the interfacial tension (IFT) and solubilization parameters as functions of salinity for the EHWONa system. The experimental results indicate that salinity increases solubilization parameters up to a maximum value, beyond which they decrease. In this study, the optimal salinity was determined to be 100 \u0026times; 10\u0026sup3; ppm. At this optimum salinity, the middle-phase microemulsion solubilizes equal volumes of oil and water. After exceeding the optimal salinity, a further increase in salt concentration to 200 \u0026times; 10\u0026sup3; ppm decreased the water solubilization parameter. Concurrently, the microemulsion system transitioned from Winsor type I to Winsor type III, and finally to Winsor type II as salinity increased. These phase transitions can be explained by the interaction of inner droplets and interfacial bending stress. Specifically, increasing salt concentration attracts water molecules to solvate the ions. This reduces the number of water molecules available to hydrate the hydrophilic head groups of the surfactant, increasing the attraction between the head groups and reducing the effective cross-sectional area of the surfactant's hydrophilic head. Consequently, the natural curvature of the interface changes, promoting a transition toward a water-in-oil (Winsor II) microemulsion. The curvature of the interfacial film transitions from positive, to zero, to negative, corresponding to the microemulsion phase transition from oil-in-water (O/W, Winsor I), to bi-continuous (Winsor III), to water-in-oil (W/O, Winsor II). Consequently, with increasing salinity, the microemulsion system undergoes a transition where the surfactant-rich phase shifts from the lower (O/W) to the middle (bi-continuous) to the upper (W/O) phase. Accordingly, the oil solubilization parameter (Vo/Vs) increases with salinity, while the water solubilization parameter (Vw/Vs) decreases [\u003cspan additionalcitationids=\"CR38 CR39 CR40 CR41\" citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec19\" class=\"Section2\"\u003e \u003ch2\u003e3.2 Phase Diagram of the Micro Emulsion System\u003c/h2\u003e \u003cp\u003ePseudo-ternary diagrams were constructed with brine, crude oil, and a surfactant/co-surfactant mixture (S\u0026thinsp;+\u0026thinsp;Cs) as the three components. These diagrams were established for various surfactants to determine the composition of the microemulsion phase. Furthermore, formulating microemulsions with a low surfactant concentration is essential for cost reduction. Figure\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e presents the corresponding pseudo-ternary diagram for the surfactant EHWO14, formation water, and crude oil, with the microemulsion region indicated by the shaded area. The pseudo-ternary diagram in Fig.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e, which features the surfactant blend (EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs), formation water, and crude oil, shows a larger microemulsion region than those of the individual surfactants (Figs.\u0026nbsp;\u003cspan refid=\"Fig5\" class=\"InternalRef\"\u003e5\u003c/span\u003e and \u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Isopropanol, used as a co-surfactant, increases the solubility of surfactant molecules in the oil phase and enhances microemulsion stability. As shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig7\" class=\"InternalRef\"\u003e7\u003c/span\u003e, the microemulsion region was more stable for the anionic surfactant (EHWONa) than for the individual nonionic surfactant or their blends. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the phase behavior of EHWO14, its derivatives (EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs), and EHWONa at optimal salinity and different temperatures.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec20\" class=\"Section2\"\u003e \u003ch2\u003e3.3 Microscopic Investigation of the Micro Emulsion Phase Volume\u003c/h2\u003e \u003cp\u003eThe experiments were carried out using EHWO14 at 25\u0026deg;C in formation water with total dissolved solids (TDS) concentrations of 50 \u0026times; 10\u0026sup3;, 100 \u0026times; 10\u0026sup3;, and 200 \u0026times; 10\u0026sup3; ppm. A middle-phase microemulsion formed at a 1:1 oil-to-water ratio, as confirmed by optical microscopy. However, this microemulsion gradually separated at salinities of 50 \u0026times; 10\u0026sup3; and 200 \u0026times; 10\u0026sup3; ppm when the temperature was increased from 25\u0026deg;C to 70\u0026deg;C. The microemulsion remained stable at a salinity of 100 \u0026times; 10\u0026sup3; ppm across all three temperatures. As the temperature increased, the oil viscosity decreased, leading to the agglomeration of oil droplets in the upper phase. The blend (EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs) was used to prepare the microemulsions at 25\u0026deg;C and three different salinities. After settling, the largest microemulsion region was observed at the salinity of 100 \u0026times; 10\u0026sup3; ppm. A microemulsion formed at salinities of 50 \u0026times; 10\u0026sup3; and 100 \u0026times; 10\u0026sup3; ppm, but the region decreased at 200 \u0026times; 10\u0026sup3; ppm. This behavior is likely due to achieving a minimum interfacial tension of 2 \u0026times; 10⁻\u0026sup2; mN/m. As the temperature increased, the microemulsion region gradually decreased. However, analysis of microscopic data for the anionic surfactant EHWONa at the optimal salinity of 100 \u0026times; 10\u0026sup3; ppm showed that the microemulsion region was largest and most stable at 50\u0026deg;C. Microemulsions are highly sensitive to elevated temperatures; this thermal instability must be balanced during the formulation of a surfactant flooding process [\u003cspan additionalcitationids=\"CR44 CR45 CR46 CR47\" citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e\u0026ndash;\u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e].\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec21\" class=\"Section2\"\u003e \u003ch2\u003e3.4 Factors Effect on Phase Behavior\u003c/h2\u003e \u003cp\u003e \u003cstrong\u003eMolecular Structure\u003c/strong\u003e \u003cp\u003eMolecular structure is one of the most crucial factors affecting surfactant performance. In this study, modifications to the molecular structure played a vital role in phase behavior. The data show that anionic surfactants are more efficient than nonionic surfactants when used individually, while surfactant blends produced the most stable microemulsions.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eSurfactant Concentration\u003c/strong\u003e \u003cp\u003eSurfactant concentration was maintained at the critical micelle concentration (CMC), as this value represents the point of maximum efficiency. However, for the flooding process, the surfactant was injected at a concentration slightly above the CMC to compensate for losses due to adsorption onto the rock surface.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eCosolvents\u003c/strong\u003e \u003cp\u003eCo-solvents, like isopropanol, increase microemulsion stability by enhancing the solubility of surfactant molecules in the oil phase.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eSalinity\u003c/strong\u003e \u003cp\u003eSalinity significantly influenced the phase behavior, with an optimal salinity observed at 100 \u0026times; 10\u0026sup3; ppm. Increasing the salinity raised the oil solubilization ratio while decreasing the water solubilization ratio. In distilled water, a balance exists between monolayer surfactant adsorption at the interface and micellization. Furthermore, hydrogen bond formation induces significant coiling of the ethylene oxide groups, which increases the minimum area per molecule (A\u003csub\u003emin\u003c/sub\u003e) and decreases the maximum surface concentration (Γ\u003csub\u003emax\u003c/sub\u003e). Conversely, in formation water, the high salt concentration disrupts hydrogen bonding, which reduces A\u003csub\u003emin\u003c/sub\u003e and increases Γ\u003csub\u003emax\u003c/sub\u003e. This mechanism is critical for enhanced oil recovery (EOR), as the increased oil solubilization at the interface improves the overall efficiency of the process.\u003c/p\u003e \u003c/p\u003e \u003cp\u003e \u003cstrong\u003eTemperature\u003c/strong\u003e \u003cp\u003eTemperature is a critical parameter for surfactant-based enhanced oil recovery due to its significant influence on surfactant molecules at the interface and within the bulk brine phase. Figure\u0026nbsp;\u003cspan refid=\"Fig8\" class=\"InternalRef\"\u003e8\u003c/span\u003e shows the effect of temperature on microemulsion phase behavior. As temperature increases, thermal agitation reduces the number of surfactant molecules at the interface, thereby increasing the minimum area per molecule (Amin). However, at specific temperatures, the formation of thermodynamically stable microemulsions can improve oil displacement and increase the EOR efficiency. While the volume fraction of the aqueous phase remains largely constant with increasing temperature, the volume of the middle phase decreases considerably as excess oil is released. This reduction continues up to a specific temperature, beyond which the middle-phase volume stabilizes [\u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e]. There are also factors such as crude oil type and water-oil ratio.\u003c/p\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec22\" class=\"Section2\"\u003e \u003ch2\u003e3.5 Contact Angle and Wettability Alteration\u003c/h2\u003e \u003cp\u003eThe contact angle of crude oil is influenced by surface charge density. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e illustrates the contact angle for crude oil on clean, loose sandstone samples (Arenite with mineralized SiO₂) treated with the surfactant EHWO14 and its blend formulations (EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs). According to Table\u0026nbsp;\u003cspan refid=\"Tab2\" class=\"InternalRef\"\u003e2\u003c/span\u003e, the contact angle of the untreated oil droplet was highly obtuse (159\u0026deg;), indicating an oil-wet rock phase. Treatment with surfactant formulations shifted the wettability to a water-wet state. Surfactants facilitate this change by reducing the interfacial tension (IFT) and contact angle, thereby lowering the adhesion work required to separate oil droplets from the rock surface and mobilize them. This reduction in adhesion work is essential for enhancing oil recovery. The temporal evolution of the contact angle is termed the dynamic contact angle. Figure\u0026nbsp;\u003cspan refid=\"Fig9\" class=\"InternalRef\"\u003e9\u003c/span\u003e shows this dynamic behavior, demonstrating that the presence of surfactant in the flooding formulations consistently reduces the contact angle over time. When surfactant adsorbs onto the oil droplet, its stability decreases, promoting rupture. In this study, surfactant adsorption at the oil-water interface formed a monolayer that rendered the oil droplet surface more hydrophilic. This promotes the formation of low-viscosity oil-in-water emulsions, thereby improving oil displacement and enhancing EOR efficiency [\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e, \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e].\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab2\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003ePhysical Terms of EHWO14 and its Blends\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurfactant\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDesignation\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eHLB\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eStatic\u003c/p\u003e \u003cp\u003eIFT\u003c/p\u003e \u003cp\u003e(mN/m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eDynamic IFT\u003c/p\u003e \u003cp\u003e(mN/m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eStatic\u003c/p\u003e \u003cp\u003eContact Angle(Ө)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eDynamic\u003c/p\u003e \u003cp\u003eContact Angle(Ө)\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e1- Ethoxylated Hydrolyzed Waste Cooking Oil (eo\u0026thinsp;=\u0026thinsp;14)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEHWO14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e4\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e27\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e2- Ethoxylated Hydrolyzed Waste Cooking Oil (eo\u0026thinsp;=\u0026thinsp;14) + alkyl Benzene sulfonate (eo\u0026thinsp;=\u0026thinsp;14)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEHWO14\u003c/p\u003e \u003cp\u003e+EABS14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e14.6\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e8\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e35\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003e3- Ethoxylated Hydrolyzed Waste Cooking Oil (eo\u0026thinsp;=\u0026thinsp;14) + Ethoxylated alkyl Benzene sulfonate (eo\u0026thinsp;=\u0026thinsp;14)\u0026thinsp;+\u0026thinsp;Co Surfactants\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eEHWO14\u003c/p\u003e \u003cp\u003e+EABS14\u0026thinsp;+\u0026thinsp;Cs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e12.4\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003e1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003e1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e22\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec23\" class=\"Section2\"\u003e \u003ch2\u003e3.6 Work Adhesion\u003c/h2\u003e \u003cp\u003eWettability is an essential property in many surfactant applications. The contact angle (θ) of a liquid on a solid surface is influenced by the reduction in surface tension induced by a surfactant. This angle is governed by the liquid's surface tension, the solid's surface energy, and the solid-liquid interfacial tension. Furthermore, the arrangement and alignment of surfactant molecules at the solid-liquid interface directly affect the work of adhesion (Wa). The extent of wetting can be described by the difference between the work of adhesion (Wa) and the work of cohesion (Wc). Both the work of adhesion and the contact angle are dependent on the composition and surface tension properties of the solid and liquid. The residual oil saturation decreases as the contact angle at the fluid/rock/oil interface increases. The surfactant molecules present in the flooding solution penetrate this interface and adsorb onto the rock surface. The contact angle increases towards the oil but decreases towards the surfactant liquid/rock. This change caused the oil to ripple and detach from the sandstone surface, forming an oil-in-water (O/W) emulsion. As a result, the amount of recovered oil increased. The following mechanism details the process of oil recovery by surfactant. The adsorption of surfactant molecules onto the rock surface is a physical process. Wettability alteration involves several steps:\u003c/p\u003e \u003cp\u003e \u003col\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eInitial State: Oil droplets initially wet the rock surface, characterized by a high contact angle (θ \u0026gt;\u0026gt; 90\u0026deg;), indicating a strongly oil-wet condition.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003ePre-CMC Surfactant Addition: Surfactant is added at a concentration below its Critical Micelle Concentration (CMC). At this monomeric phase, adsorption is minimal. Although the contact angle decreases slightly, the system remains oil-wet (θ\u0026thinsp;\u0026gt;\u0026thinsp;90\u0026deg;).\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eAt the CMC: When the surfactant concentration reaches the CMC, a monolayer of molecules penetrates the oil-rock interface, significantly reducing the interfacial tension (IFT). Simultaneously, the oil droplets and formation water develop a stable electrical double layer. This causes the contact angle to decrease below 90\u0026deg; (θ\u0026thinsp;\u0026lt;\u0026thinsp;90\u0026deg;), indicating a shift in wettability.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003ePost-CMC Dynamics: Over time, the dynamic IFT shows a further reduction, and the contact angle decreases even more (θ \u0026lt;\u0026lt; 90\u0026deg;). At this point, the sand rock surface becomes nearly water-wet, covered by a complete monolayer of adsorbed surfactant.\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003cspan\u003e \u003cli\u003e \u003cp\u003eFinal Recovery: Ultimately, the oil viscosity is reduced, achieving complete wettability alteration and forming an oil-in-water (O/W) emulsion. The recovery factor reaches its maximum value through the action of a nonionic surfactant blend with a cosurfactant (EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs). This mechanism was discussed in previous work [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e].\u003c/p\u003e \u003c/li\u003e \u003c/span\u003e \u003c/ol\u003e \u003c/p\u003e \u003cp\u003eThe work of adhesion was calculated using the Young-Dupre equation (Eq.\u0026nbsp;5) and the results are listed in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab3\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eWork Adhesion and Surface Free Energy of EHWO14 and its Blend\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026times;\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026times;\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSurfactant\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eStatic ST\u003c/p\u003e \u003cp\u003e(mN/m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eStatic IFT\u003c/p\u003e \u003cp\u003e(mN/m)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eStatic Contact Angle(Ө)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWork Adhesion,\u003c/p\u003e \u003cp\u003eWa\u003c/p\u003e \u003cp\u003e(mJ/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSurface Free Energy, γ\u003csub\u003eS\u003c/sub\u003e\u003c/p\u003e \u003cp\u003e(mJ/m\u003csup\u003e2\u003c/sup\u003e)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eSpreading coefficient,Ws\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eBlank\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e67\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e19.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e155\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e6\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e-2\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-0.127\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWO14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e28.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e4\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e5\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-4\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWO14\u0026thinsp;+\u0026thinsp;EABS14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e25.2\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e40\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e4\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e4\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-5\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003e21.8\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003e1\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e25\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c5\"\u003e \u003cp\u003e4\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c6\"\u003e \u003cp\u003e7\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;2\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003e-2\u0026times;10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003eWa\u0026thinsp;=\u0026thinsp;γ\u003csub\u003eL\u003c/sub\u003e (cos Ө + 1) (5)\u003c/p\u003e \u003cp\u003eThe Young-Dupre equation relates the work of adhesion to the interfacial tension (IFT) of the liquid (γ\u003csub\u003eL\u003c/sub\u003e) and the contact angle (θ). The difference between the work of adhesion of the solution to the surface (Wa) and the work of cohesion (Wc) provides information about the wettability of the process. According to the data in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the work of adhesion for the blend (EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs) was 4 \u0026times; 10⁻\u0026sup2; mJ/m\u0026sup2;, which is lower than that of the individual surfactant EHWO14 (5 \u0026times; 10⁻\u0026sup1; mJ/m\u0026sup2;). This lower Wa value for the blend corresponds to its lower interfacial tension (IFT), indicating a positive correlation between work of adhesion and IFT.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec24\" class=\"Section2\"\u003e \u003ch2\u003e3.7 Surface Charge Energy\u003c/h2\u003e \u003cp\u003eThe surface free energy, which determines the wetting and adhesion characteristics of a material, can be calculated using a contact angle measurement method. The specific calculation is given by Eq.\u0026nbsp;6.\u003c/p\u003e \u003cp\u003eγ\u003csub\u003eL\u003c/sub\u003e cos Ө = Ө γ\u003csub\u003eS\u003c/sub\u003e γ\u003csub\u003eSL\u003c/sub\u003e (6)\u003c/p\u003e \u003cp\u003eWhere γ\u003csub\u003eL\u003c/sub\u003e is the surface tension of the liquid (mN/m), γ\u003csub\u003eS\u003c/sub\u003e is the surface free energy of the rock, and γ\u003csub\u003eSL\u003c/sub\u003e is the interfacial tension of the used system.\u003c/p\u003e \u003cp\u003eBy rearranging Eq.\u0026nbsp;6.\u003c/p\u003e \u003cp\u003eγ\u003csub\u003eS\u003c/sub\u003e\u0026thinsp;=\u0026thinsp;γ\u003csub\u003eL\u003c/sub\u003e cos Ө / Ө γ\u003csub\u003eSL\u003c/sub\u003e (7)\u003c/p\u003e \u003cp\u003eBased on the data in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the surface free energy of the surfactant blend (EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs) was 7 \u0026times; 10⁻\u0026sup2; mJ/m\u0026sup2;. This value is lower than that of the individual surfactant EHWO14 (1 \u0026times; 10⁻\u0026sup1; mJ/m\u0026sup2;). The lower surface free energy observed for the blend can be attributed to its correspondingly lower interfacial tension (IFT) compared to the individual surfactants.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec25\" class=\"Section2\"\u003e \u003ch2\u003e3.8 Spreading Coefficient of Surfactant on the Rock Surface\u003c/h2\u003e \u003cp\u003eThe spreading coefficient is a mathematical expression that describes how a liquid spreads on a solid surface, based on the difference between the work of adhesion and cohesion. For this study, the spreading coefficient of surfactant molecules on sandstone was determined using Eq.\u0026nbsp;8.\u003c/p\u003e \u003cp\u003eWs\u0026thinsp;=\u0026thinsp;γ\u003csub\u003eL\u003c/sub\u003e (cos Ө \u0026minus;\u0026thinsp;1) (8)\u003c/p\u003e \u003cp\u003eWhere Ws is the spreading coefficient, γL is the IFT, and Ө is the contact angle. The spreading coefficient can be used as a wettability index because it increases with the wettability of oil-covered rock. The blend EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs has a spreading coefficient of -2 \u0026times; 10⁻\u0026sup3;, which is less negative than the value of -4 \u0026times; 10⁻\u0026sup2; for the individual surfactant EHWO14. This indicates a higher wettability for the blend [\u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e]. According to the data in Table\u0026nbsp;\u003cspan refid=\"Tab3\" class=\"InternalRef\"\u003e3\u003c/span\u003e, the negative spreading coefficient indicates that the rock is more water-wet than oil-wet, which is favorable for enhanced oil recovery (EOR). The coefficient is calculated using the equation Ws\u0026thinsp;=\u0026thinsp;γ\u003csub\u003eL\u003c/sub\u003e (cos θ \u0026minus;\u0026thinsp;1), which shows its dependence on both interfacial tension (IFT) and contact angle. A negative spreading coefficient, often achieved by reducing the IFT, is desirable as it promotes the release of oil droplets from the rock surface. Additionally, isopropanol acts as a co-surfactant and influences the spreading coefficient by reducing the IFT. For the blend containing isopropanol, the spreading coefficient has the highest value) among the samples tested.\u003c/p\u003e \u003c/div\u003e \u003cdiv id=\"Sec26\" class=\"Section2\"\u003e \u003ch2\u003e3.9 Enhanced Oil Recovery Factor of the Surfactant Flooding\u003c/h2\u003e \u003cp\u003eThe key to surfactant flooding in enhanced oil recovery (EOR) is designing a surfactant slug with an optimal concentration. This process is influenced by various parameters, including temperature, critical micelle concentration (CMC), adsorption characteristics on the sand-packed model, interfacial tension, contact angle, and wettability alteration at the core-formation water interface. Flooding experiments were conducted for EHWO14 and its blends, both with and without the co-surfactant isopropanol. The experiments were performed at slightly above CMC concentrations, using different temperatures (50\u0026deg;C, 70\u0026deg;C) and salinities (50 \u0026times; 10\u0026sup3;, 100 \u0026times; 10\u0026sup3;, 200 \u0026times; 10\u0026sup3; ppm) on a sand-packed model. The co-surfactant reduces the interfacial tension (IFT), which improves microemulsion stability by enhancing the solubility of surfactant molecules in the oil phase. This mechanism ultimately leads to a higher recovery factor (RF). As shown in Table\u0026nbsp;\u003cspan refid=\"Tab4\" class=\"InternalRef\"\u003e4\u003c/span\u003e, which presents the cumulative oil recovery percentages for EHWO14 and its blends, the maximum RF of 79% was achieved by the blend EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs at a salinity of 100 \u0026times; 10\u0026sup3; ppm and a temperature of 50\u0026deg;C. The action of surfactant molecules at the interface creates a complete adsorbed layer and a stable electric double layer. This leads to a reduction in interfacial tension (IFT) and, consequently, an increase in the oil recovery factor. To characterize this behavior, the solubilization parameters and phase behavior of the prepared surfactants were determined at different temperatures and salinities. The best performance, as shown in Figs.\u0026nbsp;\u003cspan refid=\"Fig10\" class=\"InternalRef\"\u003e10\u003c/span\u003e and \u003cspan refid=\"Fig11\" class=\"InternalRef\"\u003e11\u003c/span\u003e, was achieved by the surfactants and their blends at a salinity of 100 \u0026times; 10\u0026sup3; ppm and a temperature of 50\u0026deg;C. These results are attributed to the specific properties and behavior of the surfactants. Furthermore, maximum oil solubilization occurred at the optimal salinity and at concentrations above the critical micelle concentration (CMC). Conversely, recovery is low at concentrations both below and above the CMC. At concentrations significantly above the CMC, increased surfactant adsorption can form multilayers, leading to water-in-oil (W/O) emulsion that impedes oil recovery. The mechanism by which concentration affects the recovery factor was discussed in previous work [\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e]. Figure\u0026nbsp;\u003cspan refid=\"Fig12\" class=\"InternalRef\"\u003e12\u003c/span\u003e illustrates a novel mechanism proposed in this study, explaining how both traditional (individual) surfactants and their blends affect the recovery factor (RF). For surfactant blends, the molecules form well-organized adsorbed monolayers at the interface. This configuration promotes efficient stripping of oil droplets from the pore surfaces, forming an oil-in-water (O/W) emulsion. This emulsion has lower viscosity, thereby increasing the recovery factor. In contrast, traditional surfactants initially form a successful adsorbed monolayer. However, they tend to subsequently develop a multi-layer or double-layer structure. This leads to an inversion of the emulsion type from O/W to water-in-oil (W/O), which increases viscosity and ultimately decreases the recovery factor.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab4\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eCumulative Oil Recovery Percent at Different Salinities and Different Temperatures for EHWO14 and its Blends\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"10\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\"\u0026times;\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c8\" colnum=\"8\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c9\" colnum=\"9\"\u003e\u003c/div\u003e \u003cdiv align=\"char\" char=\".\" class=\"colspec\" colname=\"c10\" colnum=\"10\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSubject\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eSalinity\u003c/p\u003e \u003cp\u003e(ppm)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\" morerows=\"1\" rowspan=\"2\"\u003e \u003cp\u003eTemperature\u003c/p\u003e \u003cp\u003e(\u0026deg;C)\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c5\" namest=\"c4\"\u003e \u003cp\u003eSec.\u003c/p\u003e \u003cp\u003eRecovery\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c7\" namest=\"c6\"\u003e \u003cp\u003eTer.\u003c/p\u003e \u003cp\u003eRecovery\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eResidual\u003c/p\u003e \u003cp\u003eoil\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colspan=\"2\" nameend=\"c10\" namest=\"c9\"\u003e \u003cp\u003eTotal Recovery\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eCC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003e%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003e%\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c8\"\u003e \u003cp\u003eCC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c9\"\u003e \u003cp\u003eCC\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c10\"\u003e \u003cp\u003e%\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWO14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e50 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e58.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e48.33\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e21.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e35.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e62.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e79.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e66.45\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWO14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e100 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e55.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e45.83\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e33.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e50.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e61.53\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e88.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e71.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWO14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e100 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e54.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e47.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e26.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e42.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e60.81\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e80.19\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e66.82\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWO14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e200 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e53.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e44.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e25.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e37.31\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e67.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e78\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e65.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEABS14\u0026thinsp;+\u0026thinsp;EHWO14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e200 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e53.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e44.16\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e34.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e50.73\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e68.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e87.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e72.91\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEABS14\u0026thinsp;+\u0026thinsp;EHWO14+Cs\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e100 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e56.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e46.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e34.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e53.12\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e64.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e90\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e79.00\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWONa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e100 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e56.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e48.69\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e32.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e54.23\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e59.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e88\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e73.33\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWONa\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e100 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e56.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e47.08\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e27.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e42.51\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e63.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e83.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e69.58\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWONa+EHWO14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e100 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e58.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e48.75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e29.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e47.15\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e61.50\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e87.5\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e72.91\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eEHWONa+EHWO14\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\"\u0026times;\" colname=\"c2\"\u003e \u003cp\u003e100 \u0026times;10\u0026sup3;\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c3\"\u003e \u003cp\u003e70\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c4\"\u003e \u003cp\u003e56.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c5\"\u003e \u003cp\u003e46.66\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c6\"\u003e \u003cp\u003e19.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c7\"\u003e \u003cp\u003e29.68\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c8\"\u003e \u003cp\u003e64.00\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c9\"\u003e \u003cp\u003e75\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"char\" char=\".\" colname=\"c10\"\u003e \u003cp\u003e62.50\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003c/div\u003e"},{"header":"4. Conclusions","content":"\u003cp\u003eThis study introduced various green surfactants\u0026mdash;including nonionic, anionic, and blended types based on aliphatic and aromatic moieties prepared from waste cooking oil\u0026mdash;for improving crude oil recovery. The main conclusions are as follows:\u003c/p\u003e \u003cp\u003e \u003cul\u003e \u003cli\u003e \u003cp\u003eAt 50\u0026deg;C and a salinity of 100 \u0026times; 10\u0026sup3; ppm, the EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs blend reduced the interfacial tension (IFT) to 1 \u0026times; 10⁻\u0026sup3; mN/m. This decrease was more significant than those achieved by EHWO14 alone (1 \u0026times; 10⁻\u0026sup2; mN/m) and the EHWO14\u0026thinsp;+\u0026thinsp;EABS14 blend (8 \u0026times; 10⁻\u0026sup2; mN/m).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eAt 50\u0026deg;C and a salinity of 100 \u0026times; 10\u0026sup3; ppm, the EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs blend reduced the contact angle from 159\u0026deg; to 22\u0026deg;. In contrast, the contact angles for EHWO14 and the EHWO14\u0026thinsp;+\u0026thinsp;EABS14 blend were 27\u0026deg; and 35\u0026deg;, respectively. The phase behavior and solubilization parameters were investigated for all prepared surfactants at different temperatures (25, 50, and 70\u0026deg;C) and salinities (50\u0026times;10\u0026sup3;, 100\u0026times;10\u0026sup3;, and 200 \u0026times; 10\u0026sup3; ppm).\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe minimum interfacial tension was achieved at the optimal salinity of 100 \u0026times; 10\u0026sup3; ppm.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe microscopy study demonstrated that the anionic surfactant enhanced oil-in-water emulsion formation more effectively than the individual nonionic surfactants. However, the nonionic surfactant blends were found to be preferable as they produced more stable emulsions.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eData for the work of adhesion (Wa), surface free energy (γs), and spreading coefficient (Ws) indicate that the surfactant blends minimize interfacial tension, increase oil solubility, separate oil droplets from the rock surface, and mobilize the oil as an oil-in-water emulsion.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe total oil recovery at 50\u0026deg;C and a salinity of 100 \u0026times; 10\u0026sup3; ppm was 71% for EHWO14, 72.91% for the EHWO14\u0026thinsp;+\u0026thinsp;EABS14 blend, and 69.58% for EHWONa.\u003c/p\u003e \u003c/li\u003e \u003cli\u003e \u003cp\u003eThe highest crude oil recovery (79%) was achieved by the EHWO14\u0026thinsp;+\u0026thinsp;EABS14+Cs blend at 50\u0026deg;C and a salinity of 100 \u0026times; 10\u0026sup3; ppm. These results demonstrate the potential of these waste-based surfactants for enhanced oil recovery applications.\u003c/p\u003e \u003c/li\u003e \u003c/ul\u003e \u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e \u003ch2\u003eCompeting Interests\u003c/h2\u003e \u003cp\u003eThe authors have no relevant financial or non-financial interests to disclose.\u003c/p\u003e \u003c/p\u003e\u003cp\u003e \u003ch2\u003e \u003cb\u003eConflicts of interest\u003c/b\u003e:\u003c/h2\u003e \u003cp\u003eThere are no conflicts of interest to declare.\u003c/p\u003e \u003c/p\u003e\u003ch2\u003eFunding\u003c/h2\u003e \u003cp\u003eThe authors declare that no funds, grants, or other support were received during the preparation of this manuscript.\u003c/p\u003e\u003ch2\u003eAuthor Contribution\u003c/h2\u003e\u003cp\u003eAll authors contributed to the study conception and design. Material preparation, data collection, and analysis were performed by prof. Dr. Ahmed Mohamed El-Sabagh, prof. Dr. Fatma Hosny Abdel-Salam, and Dr. Asmaa Mohamed. The first draft of the manuscript was written by Dr. Asmaa Mohamed, and all authors commented on previous versions of the manuscript. All authors read and approved the final manuscript.\u003c/p\u003e\u003ch2\u003eAcknowledgement\u003c/h2\u003e\u003cp\u003eThe authors acknowledge the Egyptian Academy of Scientific Research and Technology (ASRT) for sharing Project 56/2015 (Construction of a semi-pilot plant for enhanced oil recovery (EOR) by unconventional methods) (2015\u0026ndash;2018) with the Egyptian Petroleum Research Institute (EPRI). The authors should also thank all members of the EPRI-EOR/IOR Project.\u003c/p\u003e\u003ch2\u003eData Availability\u003c/h2\u003e\u003cp\u003eThe raw datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eEl-Masry, J. F., Bou-Hamdan, K. 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Phase behaviour and characterization of microemulsion stabilized by a novel synthesized surfactant: Implications for enhanced oil recovery. \u003cem\u003eFuel\u003c/em\u003e \u003cb\u003e235\u003c/b\u003e, 995\u0026ndash;1009 (2019).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePal, N., Saxena, N. \u0026amp; Mandal, A. Phase Behavior, Solubilization, and Phase Transition of a Microemulsion System Stabilized by a Novel Surfactant Synthesized from Castor Oil. \u003cem\u003eJ. Chem. Eng. Data\u003c/em\u003e. \u003cb\u003e62\u003c/b\u003e, 1278\u0026ndash;1291 (2017).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003eAl-Sabagh, A. M., Abdel-Salam, F. H., Mohamed, A., SOLUBLIZATION PARAMETERS \u0026amp; AND PHASE BEHAVIOR OF ECO FRIENDLY SURFACTANTS-BRINE-OIL MICROEMULSION FOR ENHANCED OIL RECOVERY.. \u003cem\u003eProcesses Petrochemistry Oil Refin.\u003c/em\u003e \u003cb\u003e24\u003c/b\u003e, (2023).\u003c/span\u003e\u003c/li\u003e \u003cli\u003e\u003cspan\u003ePackham, D. E. Work of adhesion: contact angles and contact mechanics. \u003cem\u003eInt. J. Adhes. Adhes.\u003c/em\u003e \u003cb\u003e16\u003c/b\u003e, 121\u0026ndash;128 (1996).\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"(Ecofriendly surfactants, Waste cooking oil, phase behavior, Interfacial tension, Enhanced oil recovery)","lastPublishedDoi":"10.21203/rs.3.rs-8595521/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-8595521/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eEnhanced oil recovery (EOR) is a tertiary method used to extract crude oil remaining in reservoirs. With growing concerns about waste generation and its environmental impacts, waste cooking oil (WCO) has emerged as both a pollutant and a valuable renewable feedstock. WCO can be efficiently converted into sustainable surfactants with favorable surface and interfacial properties suitable for reservoir conditions. In this study, anionic and nonionic surfactants were synthesized from WCO: ethoxylated dodecylbenzene sulfonate (EABS14, aromatic) and ethoxylated hydrolyzed waste oil (EHWO14, aliphatic). Isopropanol was incorporated as a co-surfactant to enhance microemulsion performance. Phase behavior was evaluated at salinities of 50\u0026times;10\u0026sup3;, 100\u0026times;10\u0026sup3;, and 200\u0026times;10\u0026sup3; ppm and at temperatures of 50 and 70\u0026deg;C. Solubilization parameters and microemulsion phase volumes were used to determine optimal conditions. At optimum salinity, dynamic interfacial tension (IFT) decreased significantly, reaching 1\u0026times;10⁻\u0026sup2;, 8\u0026times;10⁻\u0026sup2;, and 1\u0026times;10⁻\u0026sup3; mN/m for EHWO14, EHWO14\u0026thinsp;+\u0026thinsp;EABS14, and EHWO14\u0026thinsp;+\u0026thinsp;EABS14+CS, respectively. Contact angles were reduced from 155\u0026deg; to 27\u0026deg;, 35\u0026deg;, and 22\u0026deg;, indicating effective wettability alteration. Flooding experiments confirmed the efficiency of WCO-derived surfactants, with maximum oil recovery at 100\u0026times;10\u0026sup3; ppm and 50\u0026deg;C. Recovery factors were 71.00% for EHWO14, 73.33% for EHWONa, 72.91% for EHWONa+EHWO14, and highest at 79.00% for the EHWO14\u0026thinsp;+\u0026thinsp;EABS14+CS blend. These results demonstrate that WCO valorization into surfactants provides an eco-friendly and effective EOR alternative.\u003c/p\u003e","manuscriptTitle":"Conversion of Waste Cooking Oil to Environmentally Acceptable Surfactants for Enhanced Oil Recovery","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-03-31 12:21:06","doi":"10.21203/rs.3.rs-8595521/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2026-04-06T06:26:03+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-04-03T08:58:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"311966223397708724580270361189026742121","date":"2026-04-02T02:45:48+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"215409247113711059644280381465531542032","date":"2026-04-01T06:42:52+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2026-03-30T14:08:02+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"172613758890774328941029307102313167457","date":"2026-03-30T13:06:22+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"225740192227897150562750764672710980752","date":"2026-03-30T02:58:04+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"219321229142064181066135886329959102249","date":"2026-03-29T12:56:59+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"192101904358047469196627015114069497571","date":"2026-03-28T06:35:13+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"35884511346460702205832266028860884776","date":"2026-03-27T12:03:11+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-03-27T11:48:27+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-03T05:12:06+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-01-26T22:20:04+00:00","index":"","fulltext":""},{"type":"submitted","content":"Scientific Reports","date":"2026-01-26T22:13:07+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"scientific-reports","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"scirep","sideBox":"Learn more about [Scientific Reports](http://www.nature.com/srep/)","snPcode":"","submissionUrl":"","title":"Scientific Reports","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"stoa","reportingPortfolio":"Scientific Reports","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"2281e2f2-f71f-4e29-a5a4-c6438ad38b44","owner":[],"postedDate":"March 31st, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"in-revision","subjectAreas":[{"id":65403489,"name":"Physical sciences/Chemistry"},{"id":65403490,"name":"Physical sciences/Energy science and technology"},{"id":65403491,"name":"Physical sciences/Engineering"},{"id":65403492,"name":"Earth and environmental sciences/Environmental sciences"}],"tags":[],"updatedAt":"2026-05-12T04:39:29+00:00","versionOfRecord":[],"versionCreatedAt":"2026-03-31 12:21:06","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-8595521","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-8595521","identity":"rs-8595521","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}