Impact of Surfactant Mixtures on Microemulsion Phase Behavior

Surfactant mediated enhanced oil recovery techniques such as surfactant-polymer (SP), and alkaline-surfactant-polymer (ASP) flooding, have received increased attention in the past decade due to their ability to reduce capillary forces at the pore-scale to ultra-low values and mobilize oil. In order to improve the economics of such processes, a better understanding of the interaction of surfactant-oil-brine systems is needed. Recently, an equation-of-state (EoS) has been developed that significantly improves microemulsion phase behavior prediction based on coupling of the HLD-NAC equations with a new correlation of optimum conditions, and an updated hydrophilic-lipophilic difference (HLD) model that includes pressure (Ghosh and Johns 2014, 2016). The new EoS accounts for gradients in key formulation properties relevant for reservoir-scale processes in a robust and noniterative framework. One common assumption of all existing microemulsion phase behavior models is the assumption of pure excess phases, which says that the surfactant component can only be present in the microemulsion phase. The focus of this paper is to allow for surfactant partitioning into both the water and oil excess phases, and then relate the relevant surfactant partitioning coefficients to the HLD state function so that K-values, and potentially phase behavior, can be predicted. This paper derives important relations of the surfactant partition coefficient between relevant phases based on a chemical potential description of the HLD, which measures the deviation from optimum conditions. In particular, we calculate the surfactant partition coefficients from numerous experiments in the literature and show that the surfactant partitioning coefficient has a linear scaling with HLD for a wide variety of formulation variables. Surfactant K-values between excess phases from all experiments examined collapse onto the same linear relationship so that once HLD is known (based on formulation variables such as salinity) the K-values are explicitly determined. The estimation of surfactant partition coefficients can be used to aid the design of surfactant formulations for EOR processes.

Predicting microemulsion phase behavior using physics based HLD-NAC equation of state for surfactant flooding

The surface chemical behaviour of phthalate esters in oil–water mixtures, both in the presence and absence of a conventional surfactant, has been investigated. We have estimated the surface activity of phthalate esters and the extent to which this type of moderately polar oil can be coadsorbed into concentrated monolayers of conventional surfactants at the oil/water interface. In the absence of surfactant, phthalate oils are adsorbed from dilute solution in heptane at the heptane/water interface, exhibiting a surface activity typical of non-aromatic diesters and similar to that of alcohols. However, the surface chemical and microemulsion phase behaviour in mixtures of phthalate oils and aqueous NaCl solutions in the presence of the anionic surfactant sodium bis(2-ethylhexyl) sulfosuccinate (AOT) indicates a low extent of penetration of the phthalate oils into AOT monolayers. This is interesting since the phthalates have similar surface activities (from hydrocarbon oils) to alcohols which are very effective cosurfactants capable of strong coadsorption into surfactant monolayers. The main effects of substituting phthalate oils for alkanes in mixtures of oil–AOT–aqueous NaCl are (i) to increase the critical aggregate concentration of surfactant in the oil phase, (ii) to increase the NaCl concentration required for microemulsion phase inversion and (iii) to increase the magnitude of the minimum interfacial tension obtained by varying the salt concentration. It is concluded that phthalate oils do not act as strongly adsorbed cosurfactants in AOT–water–oil systems and the extent of phthalate oil penetration of AOT monolayers is less than for alkanes.

On the random Interface models of microemulsions as the foundation of hydrophilic-lipophilic difference - net average curvature (HLD-NAC) equation of state.

This study addresses the challenge of recovering oil in the VIII+IX Reservoir in Shuanghe oil field in Henan Province, China, a mature reservoir with a 91% water cut and a temperature as high as 100°C. The objective is to develop a cost-effective surfactant blend with ultra-high interfacial efficiency and strong interactions with heavy oil fractions, aiming to enhance recovery where conventional methods are inadequate. The surfactant blend was developed through molecular design, adjusting structural parameters such as carbon chain length, polymerization degree, and the ratio of anionic to cationic surfactants. Surface tension, interfacial tension (IFT), microemulsion phase behavior, and adsorption tests optimized interfacial performance while minimizing surfactant concentration. Core flooding tests were performed on a heterogeneous core model with a 3:1 permeability contrast (100×10⁻³ μm²/300×10⁻³ μm²) and dimensions of 2.5×2.5×30 cm (porosity: 15-20%). The study evaluated the surfactant-polymer (SP) microemulsion flooding (0.15% S + 0.12% P) alone and combined with profile control slugs pre- and post-injection. The surfactant blend's ultra-low Critical Micelle Concentration (CMC) of 4 mg/L reflected its strong resistance to dilution, making it particularly suitable for high water cut conditions where dilution resistance is essential for maintaining effective interfacial activity and enhancing oil recovery. Phase behavior tests showed the surfactant blend provided excellent solubilization, with parameters reaching 15. IFT achieved values of 10-3 to 10-4 mN/m across 0.025% to 0.25% concentrations. Combined with polymer, the binary system maintained ultra-low IFT at 10-4 mN/m, with thermal stability demonstrated by IFT remaining below 5×10-3 mN/m after 180 days at 100°C. Core flooding tests demonstrated a substantial improvement in oil recovery, with optimized microemulsion flooding achieving up to a 22.65% increase over water flooding at a low surfactant concentration of 0.15%. The addition of a profile control slug further raised the recovery factor to 25.23%. These results highlight the surfactant system's efficiency and effectiveness in enhancing oil recovery in complex reservoir environments. This research presents a novel surfactant system that effectively interacts with heavy oil components, maintaining ultra-low IFT at high temperatures. With high solubilization at low concentrations and excellent thermal stability, this cost-effective solution enhances oil recovery in mature, high-water cut reservoirs, providing valuable insights for the advancement of surfactant-polymer flooding in the petroleum industry.

Compound Complex Formation in Phospholipid Membranes Induced by a Nonionic Surfactant of the Oligo(ethylene oxide)–Alkyl Ether Type: A Comparative DSC and FTIR Study

Increased phospholipase A2 and lyso-phosphatidylcholine levels are associated with surfactant dysfunction in lung contusion injury in mice

Keywords: biopolymer, gelatine, dextran, PEO, phase separation, polydispersity, molar mass distribution, SEC-MALLS, CSLM The temperature-composition phase diagram of aqueous solutions of gelatine and dextran, which show liquid/liquid phase segregation, were explored at temperatures above the gelation temperature of gelatine. It turned out that the compositions of coexisting phases show practically no dependence on temperature between 40oC and 80oC. Also, the total polymer concentration at which phase separation occurred was found to be nearly independent on temperature. These observations suggest an entropy driven phase separation. Phase separation is found to be accompanied by strong fractionation of the molar mass distribution in the two phases. Molar mass distributions in coexisting phases were investigated using Size Exclusion Chromatography with MultiAngle Laser Light Scattering. The molar mass of the native material and concentration appeared to be the only factors that affected the final molar mass distributions, temperature having no effect. The results show that in the molar mass range where fractionation is the strongest, i.e. roughly below the maximum in the distribution, fractionation is governed by a Boltzmann factor , where DG denotes the free energy involved in transferring a polymer with a certain length from the enriched to the depleted phase, and in this case turns out to be proportional to the molar mass. The phase behaviour of aqueous mixtures of poly(ethylene oxide) (PEO) and dextran is also studied. From the temperature dependence we conclude that the phase separation between PEO and dextran is partly caused by sterical interactions. From the equilibrium phase volumes of the phase separated mixture and the shape of the temperature-composition phase diagram of PEO and dextran we conclude that also the decrease of solvent quality of water for PEO at increasing temperatures is involved. It is suggested that the characteristics of the PEO-water interaction can affect the degree of fractionation. This suggestion is based on the observation that the degree of fractionation is not a simple exponential function of the molar mass. Adsorption of high molar mass dextran at the interface between gelatine and dextran during the phase separation of aqueous mixtures of these two polymers is also studied. This adsorption is observed after macroscopic phase separation as well as during the phase separation. In the last case, the system is studied with Confocal Scanning Light Microscopy. For this purpose, the dextran is covalently labelled with fluorescein 5-isothiocyanate (FITC). It turns out that the adsorption of high molar mass dextran is highly affected by the labelling. The adsorption of labelled dextran leads to a stable film between the two coexisting phases, thus preventing dextran droplets to coalesce. If the degree of labelling increases above a certain level, the labelled dextran does not lead to a stable film, but is preferentially present in the gelatine-rich phase.

Gibbs ensemble Monte Carlo simulations and cloud point measurements were performed to understand the molecular weight dependence of χ and the effect of dispersity on the phase behavior of polymer mixtures. Oligomeric blends consisting of poly(ethylene-alt-propylene) (PEP) and poly(ethylene oxide) dimethyl ether (PEO) were used as the model systems. First, the molecular weight dependence of χ for PEP/PEO mixtures was studied using simulations and experiments for PEP/PEO mixtures with various molecular weights. An empirical model with a single adjustable parameter kij is used to quantify this molecular weight dependence, and it allows for the accurate prediction of χ of PEP/PEO mixtures with arbitrary molecular weights. Second, the effects of molecular weight distribution (MWD) and dispersity (Đ) of PEO on the PEP/PEO phase diagram were investigated via both simulations and experiments. When PEO is relatively monodisperse (Đ < 1.2), the phase diagram is found to be insensitive to either MWD or Đ, despite differentiation in molecular partitioning observed from simulations. However, the coexistence curve for mixtures containing PEO with a bimodal distribution and a large dispersity (Đ = 1.76) differs dramatically from that for mixtures containing low-dispersity PEO, which suggests that the former mixture can no longer be treated as a binary system. Furthermore, structural analysis was performed from simulation trajectories to probe microscopic heterogeneity and aggregation behavior in the liquid phases. The results in this work permit the accurate prediction of χ and the phase diagram of disperse binary polymeric mixtures.

The phase behavior of ternary and quaternary mixtures of water, ethylene glycol, n-dodecane and nonionic surfactant C14E6 was studied. Similarities and differences of the phase behavior between aqueous and nonaqueous systems were found. Replacing water by ethylene glycol in the quaternary system water + ethylene glycol/n-dodecane/C14E6 leads to a shift in the one-, two- and three-phase regions in the phase diagrams. The polar protic solvent ethylene glycol reduces the hydrophobic effect in the multicomponent systems. The result is a higher mutual solubility of ethylene glycol, a weaker adsorption at the internal interface and, hence, a lower solubilization capacity of the amphiphilics. The reduced amphiphilic strength of C14E6 in ethylene glycol or water + ethylene glycol mixtures corresponds to C14E6 in aqueous systems.

Prediction of microemulsion phase behavior for changing state variables is critical to formulation design of surfactant-oil-brine (SOB) systems. SOB systems find applications in various chemical and petroleum processes, including enhanced oil recovery. A dimensional equation-of-state (EoS) was recently presented by Ghosh and Johns1 that relied on estimation of the surfactant tail length and surface area. We give an algorithm for flash calculations for estimation of three-phase Winsor regions that is more robust, simpler, and noniterative by making the equations dimensionless so that estimates of tail length and surface area are no longer needed. We predict phase behavior as a function temperature, pressure, volume, salinity, oil type, oil-water ratio, and surfactant/alcohol concentration. The dimensionless EoS is based on coupling the HLD-NAC (Hydrophilic Lipophilic Difference-Net Average Curvature) equations with new relationships between optimum salinity and solubility. An updated HLD expression that includes pressure is also used to complete the state description. A significant advantage of the dimensionless form of the EoS over the dimensional version is that salinity scans are tuned based only on one parameter, the interfacial volume ratio. Further, stability conditions are developed in a simplified way to predict whether an overall compositions lies within the single, two-, or three-phase regions. Important new microemulsion relationships are also found, the most important of which is that optimum solubilization ratio is equal to the harmonic mean of the oil and water solubilization ratios in the type III region. Thus, only one experimental measurement is needed in the three-phase zone to estimate the optimum solubilization ratio, a result which can aid experimental design and improve estimates of optimum from noisy data. Predictions with changing state variables are illustrated by comparison to experimental data using standard diagrams including a new type of dimensionless fish plot. The results show that the optimum solubilization ratio and salinity using the tuned dimensionless EoS are within average errors of 2.44% and 1.17% of experimental values for the fluids examined. We then use the dimensionless equations and thermodynamic first-principles to derive the constant in Huh's equation for interfacial tension prediction.

The Time-Resolved Fluorescence Quenching Method for the Study of Micellar Systems and Microemulsions: Principle and Limitations of the Method.- Solubilization of Alcohols and Alkanediols in Aqueous Surfactant Solutions.- Thermodynamics of Solubilization into Surfactant Micelles.- Application of the Differential Conductivity Method: The Effect of Chain-Length of Homologous Surfactants on the Partition Coefficient of Alkanols Between Bulk Water and Micelles.- Mixed Micelle Theory as an Aid to Surfactant Formulation.- Partitioning of Cationic Surfactants Between Heptane and Water.- Adsorption of Sodium Dodecyl Sulfate and 1-Butanol on Solid Aluminium Oxide.- Association Models for Phenothiazine Drugs in Aqueous Solution.- Polymer-Surfactant Systems.- Kinetic and Equilibrium Studies Associated with Polymer Surfactant Interactions.- The Interaction of Amphiphiles with Molecular Assemblies and Polymers.- Step-Weighted Random Walk Statistics, as Applied to Association Colloids.- A Population Balance Model for the Determination of Solubilizate Exchange Rate Constants in Reversed Micellar Systems.- Selective Solubilisation in Reversed Micelles.- When is a Microemulsion a Microemulsion?.- Uni-And Bicontinuous Microemulsions.- Experimental and Computational Aspects of the Time-Correlated Single Photon Counting Technique.- Droplet Size and Dynamics in Water oil Microemulsions. Correlations Between Results from Time-Resolved Fluorescence Quenching, Quasielastic Light Scattering, Electrical Conductivity and Water Solubility Measurements.- The Influence of the Distribution of Salt on the Phase Behaviour of Microemulsions with Ionic Surfactants.- A Study of Microemulsion Stability.- Structure of Microemulsion-Based Organo-Gels.- Luminescence Probe Study of Organized Assemblies Treated as Fractal Objects.- Organized Assemblies in Chemical Separations.- Structural Changes of Aot Reverse Micelles by the Presence of Proteins: Percolation Process Induced by Cytochrome C.- Microparticle Formation in Reverse Micelles.- Electric Birefringence Measurements in Micellar and Colloidal Solutions.- Surfactant Liquid Crystals.- The Phase Behaviour of Metal(II) Soaps in One, Two and Three Component Systems.- Ringing Gels: Their Structure and Macroscopic Properties.- Industrial Hydrocolloids.- Kinetics of the Interaction of the Potential-Sensitive Dye Oxonol V with Lipid Vesicles.- Equilibrium and Dynamic Investigation on the Main Phase Transition of Dipalmytoylphosphatidylcholine Vesicles Containing Polypeptides: A Dsc and Iodine Laser T-Jump Study.- An Investigation on the Penetration of Lipids in the Bilayer of Stratum Corneum.- Foam Stability in Non-Aqueous Multi-Phase Systems.- The Profile of a Plateau Border Near a Vertical Foam Film.- The Anamolous Effect of Electrolytes on Surfactant Monolayer Surface Pressure-Area Isotherms.- Surfactant Molecular Geometry Within Planar and Curved Monolayers in Relation to Microemulsion Phase Behaviour.- Light Scattering Experiments on Anisotropic Latex Particles.- Electric Birefringence Studies of Micellar and Colloidal Dispersions.- Polymers at Interfaces: Statics, Dynamics and Effects on Colloidal Stability.- Equilibrium Structure and Properties of Colloidal Dispersions.- Structure, Dynamics and Equilibrium Properties of Inorganic Colloids.- The Rheology of Concentrated Dispersions of Aggregated Particles.- Rheological Properties, Interparticle Forces and Suspension Structure.- Interfacial Rheology and its Application to Industrial Processes.- Effective Interaction Potentials of Colloids from Structural Data: The Inverse Problem.- Computer Simulation of the Coagulation and Flocculation of Colloidal Particles.- Computer Simulations of Fluids and Solutions of Organic Molecules.- The form of Colloidal Crystals from Silica Latices in Nonaqueous Dispersion.- Consolidation of Depletion Flocculated Concentrated Suspensions: Influence of Non Adsorbing Polymer Concentration on Consolidation Rate Constants.- Colloidal Semiconductors.- Obtention and Characterisation of Ultrafine Magnetic Colloidal Particles in Solution.- Non-Equilibrium Double Layers in Connection with Colloid Stability.- Recent Theories on the Electric Double Layer.- Application of Double Layer Theory to Moderately Complex Systems.- Wetting Phenomena.- Thermodynamics of Adsorption from Dilute Solutions.- List of Participants.- Index of Subjects.

The dynamic effect of pressure and Oil composition on Microemulsion phase behavior, complementing the key effect of variable salinity, has been implemented in our four-fluid-phase, fully implicit in-house research reservoir simulator. This has been achieved through self-consistent coupling of a traditional Gas/Oil/Water phase equilibrium model, either compositional or generalized black-oil,—providing phase fractions, oleic composition, and aqueous salinity—with a Microemulsion model based on oleic/aqueous/chemical pseudophase equilibrium. As an application example and validation test case, we consider a hypothetical surfactant/polymer (SP) coreflood of a saturated Oil, interrupted by a progressive depressurization, during which dissolved gas is released, which shifts the Microemulsion phase state from Winsor Type III to Type II-. This proves the good functioning of our new option, and shows, yet on a simple case, that it does not degrade numerical performance, despite the introduction of additional nonlinear dependencies.

Ever since Muskat presented his approximate theory on water coning in 1935, the primary research focus has been on design and performance optimization. Subjects such as critical production rates, time for the cone to break through, and production after break-through have been studied with physical, analog, analytical and numerical simulation models. Guidelines have been developed for optimal placement of wells in a stratified system and for situations involving simultaneous coning of water and gas. For most practical situations, ultimate oil recovery was determined to be virtually independent of producing rates. This gave rise to the concepts of infilling wells in reduced spacing, producing wells at higher fluid rates, and periodic re-completion of wells to minimize coning thus mlpdmizing reserves produced. Associated problems such as haridrrng of large amounts of high water-cut effluent and treatment of effluent for the re-injection of water into the reservoir also received technological attention. The advent of horizontal wells during the 1980's resulted in a significant increase in ‘clean’ oil rates and reserves (without coning). As a result, many otherwise marginal or uneconomic pools became viable. Consequently, the research efforts were, doubled not only to optimize operations, but also to find sup: porting technology to mitigate coning. Two fundamental problems remain with conventional (vertical) and horizontal wells:Sustaining oil rates at economic levels andHandling and disposal of the effluent. Several ideas have been developed and some have been tried with varying degrees of success. These include:Placing barriers to movement of water and gas around the well. These involve introducing water, oil, gas, gels, foams, polymers, or cementing agents to preferentially reduce permeability or relative permeability to water or gas; injecting oil into the water or gas zone; injecting gas into the water zone; and injecting foam into the gas zone to reduce relative permeability to gas.Modifying flowing pressure distribution around wells by i) producing water or gas via separate completion intervals' in the same well, or ii) reversing coning of oil into water or gas zone;Minimizing operating costs via sub-surface water separation and disposal of the separated water in the same well. This paper presents a brief review of the current state-of-the-art. Introduction In many situations, recovery of oil is limited by excessive production of water or gas. After a period of low (or no) water and gas production, water-oil ratios and/or gas-oil ratios begin to increase substantially. Under these conditions, production rates may have to be restricted due to equipment, operating, regulatory, or environmental constraints. This results in not only reduced oil rates, but also in increased cost of handling (separation, processing, and disposal) of effluents and ultimately, in a rather premature shutting-in of the wells. Due to significant economic implications, the phenomenon of water and gas coning has received some attention in the literature. What is Coning? Over geological times, the reservoir fluids (oil, water, and gas) exist under static pressure (gravity-capillary) equilibrium.

New fully implicit formulations for the multicomponent surfactant-polymer flooding reservoir simulation