Phase Behavior Of Microemulsions Research Articles

Effect of CO2 Pressure on Microemulsion Phase Behavior and Displacement Efficiency in Sandstones

Effect of CO₂ Pressure on Microemulsion Phase Behavior and Displacement Efficiency in Sandstones

Rapid design and optimization of complex surfactant microemulsions for high-efficiency oil extraction processes integrating experimental and modeling approaches

Microemulsions have been widely used as a means of high-efficiency oil extraction processes in the field of oil recovery, separation, deposit removal, et al. Phase behavior is considered the most reliable evidence for formulating surfactant systems. There, however, few methods exist that can predict the phase behavior of microemulsions formed by complex surfactant compositions.This work developed a modified model based on the Hydrophilic Lipophilic Deviation-Net Average Curvature (HLD-NAC) model that could rapidly and accurately predict the phase behavior and phase evolution of complex surfactant microemulsions. The phase evolution of the microemulsions with equivalent alkane carbon number (EACN), surfactant concentration, and water–oil ratio (WOR) were explored. The results indicated that the new model successfully delineated the salinity boundaries of Winsor Type III microemulsion and predicted the inversions of phase behavior. A linear correlation between the EACN and the optimal salinity was demonstrated, with a precisely defined predictive range of EACN for Winsor Type III microemulsions. A fish diagram that illustrated the evolution path of the microemulsion phase was established through concentration scanning. The WOR test suggested that Winsor Type III microemulsion could be formed through salinity regulation once the surfactant concentration exceeded the critical micelle concentration (CMC).

Laboratory Studies of the Phase Microemulsions between Oil, Gaberoun Lake Water, and Surfactant Systems by using Phase Behavior Test

Microemulsion phase behavior is the mostimportant phenomenon related to any type of chemicalenhanced oil recovery (EOR) using surfactant. An EORprocess in which a small amount of surfactant is added to anaqueous fluid injected to sweep the reservoir. The presenceof surfactant reduces the interfacial tension between the oiland water phases to improve oil recovery. This research wasconducted through interaction with the micelles of asurfactant in a Gaberoun Lake Water (GLW), a substancespontaneously dissolves to form a stable and clear solution.The laboratory experiment was designed to solubilize the oilby GLW with oil and surfactant to form an emulsion (ME)consisting of oil and water. The GLW and surfactant waterwere prepared by different concentrations and salinity asaqueous. The aqueous was injected into special glass tubesand placed inside the oven at different temperatures from30 oC to 70 oC at ambient pressure. The glass tubes were leftuntil equilibrium condition for 72 hours. In this study, newresults using dead oil and surfactant with Libyan leak waterwere presented. The range of the thickness of the ME from0.1ml to 1.4 ml. The result showed that the ME wasdecreased with a decrease in surfactant concentration valuesand increased with a decrease salinity. The findings in thisresearch that GLW can be used for oil recovery processes.

Microemulsion phase behavior based on biodiesel and its performance in treating oil-contaminated soil

Biodiesel-based microemulsions have unique advantages in the treatment of petroleum-contaminated soils, thanks to their ultra-low interfacial tension and strong solubility. By studying the effects of different solvents, surfactants, and co-surfactants on the phase transition of the microemulsion, and comparing the effects of temperature, solid-liquid ratio, and treatment time on washing efficiency, we successfully obtained the composition of a biodiesel-based microemulsion system with high stability and optimized washing conditions. At the same time, the deactivation mechanism in the washing process of the microemulsion was analyzed. The experimental results showed that the biodiesel microemulsion, composed of SDBS as a surfactant and n-butanol as a co-surfactant, exhibited excellent washing stability. The optimized washing conditions were as follows: temperature of 35℃, 1:5 solid-liquid ratio, and 30-minute treatment time. Under these conditions, the oil removal rate reached as high as 73.6%. The reasons for the microemulsion inactivation may be as follows: (1) Composition loss of the microemulsion during the washing process leads to a reduction in washing efficiency; (2) During the washing process, solid particles formed a hard shell on the surface of the microemulsion droplets, reducing the washing efficiency; (3) Oil components eluted from the soil entered the oil phase of the microemulsion, changing the oil phase composition and resulting in decreased washing efficiency.

Impact of Injection Gas on Low-Tension Foam Process for EOR in Low-Permeability Oil-Wet Carbonates

Low-tension gas (LTG) flooding has been proven in lab-scale experiments to be a viable tertiary enhanced oil recovery (EOR) technique in low-permeability (~10 mD) oil-wet carbonates. Work carried out previously almost exclusively focused on water-wet cores. The application of LTG in oil-wet carbonates is investigated in this study along with the impact of a hydrocarbon (HC) mixture as the injection gas on oil–water microemulsion phase behavior. The optimum injection gas fraction (ratio of gas injection rate to total injection rate of gas and water) for the hydrocarbon gas mixture in oil-wet carbonates regarding the oil recovery rate was determined to be 60% as it resulted in around 50% residual oil in place (ROIP) recovery. It was shown that proper mobility control can be achieved under these conditions even in the absence of strong foam. The effect of HC gas dissolution in oil was clearly shown by replacing the injection HC gas with nitrogen under the same conditions. Furthermore, the importance of ultra-low interfacial tension (IFT) produced by the injection gas and surfactant slug is proven by comparing injection at sub-optimum salinity to injection at optimum salinity.

Phase behavior of multi-stimuli-responsive ionic liquids-based micro-emulsion and its application in nano silica synthesis and curcumin encapsulation

The enrichment and separation of trace compounds, as well as the preparation of nanomaterials, are all greatly facilitated by responsive micro-emulsion. A multi stimuli-responsive ionic liquids-based micro-emulsion system was established with alkyl-N-Tropine (trans) P-methoxycinnamate ([CnTr][PMCA], TILS) as a surfactant. The factors affecting the phase behavior of micro-emulsion, such as the structure of the TILS, cosurfactant, oil, temperature, pH, and salinity, were investigated by multiple research methods. Five zones were identified inside the micro-emulsion phase region as O/W, B.C., liquid crystal (L.C.), L.C.+B.C., and W/O. The TILS-based micro-emulsion displayed high stability at measured temperatures. High salinity contributed to a higher water solubilization capacity of the micro-emulsion. For the potential applications of the micro-emulsion, with sizes ranging from 20 to 70 nm, nanoscale silica particles showed persistent stability. High levels of drug loading rate (about 8.6 mg·g−1) and encapsulation efficiency (about 99%) of the micro-emulsion loaded with curcumin were attained.

A New Adaptive Implicit Method for Multicomponent Surfactant-Polymer Flooding Reservoir Simulation

Summary In the oil industry, chemicals can improve oil production by mobilizing trapped and bypassed oil. Such processes are known as chemical-enhanced oil recovery (CEOR). Surfactants and polymers are important chemicals used in CEOR with different mechanisms to improve oil recoveries, such as reduction in residual saturation, oil solubilization, and mobility control. However, both surfactant and polymer may increase the cost of oil production, making optimizing these processes essential. Reservoir simulators are tools commonly used when performing such field optimization. The simulation of surfactant flooding processes has been historically performed with the implicit pressure explicit composition (IMPEC) approach. The injection of surfactants requires modeling the brine/oil/microemulsion phase behavior along with other processes, such as capillary desaturation and retention. The microemulsion phase behavior and the complex relative permeability behavior can lead to convergence issues when using fully implicit (FI) schemes. Only recently, the FI approach has been efficiently applied to simulate this process using new modeling. The adaptive implicit method (AIM) can combine the benefits of the FI and IMPEC approaches by dynamically selecting the implicitness level of gridblocks in the domain. This work presents a new AIM in conjunction with recently developed models to mitigate discontinuities in the microemulsion relative permeabilities and phase behavior. The approach presented here considers the stability analysis method as a switching criterion between IMPEC and FI. To the best of our knowledge, the approach presented here is the first AIM to consider the brine/oil/microemulsion three-phase flow in its conception. The new approach uses the finite volume method in conjunction with Cartesian grids as spatial discretization and is applied here for field-scale problems. The new approach is tested for polymer flooding and surfactant-polymer (SP) flooding for problems with several active cells ranging from about a hundred thousand to almost a million. The AIM approach was compared with the FI and IMPEC approaches and displayed little variation in the computational performance despite changes in the timestep size. The AIM also obtained the fastest performance for all cases, especially for SP flooding cases. Furthermore, the results here suggest that the gap in performance between the AIM and FI seems to increase as the number of gridblocks increases.

A Systemic Comparison of Physical Models for Simulating Surfactant–Polymer Flooding

Three different reservoir simulators that utilize both two-phase and three-phase microemulsion phase behavior models are used to model surfactant–polymer flooding to determine and compare their results. Different models are used in each simulator to describe the physical behavior of injected chemicals into the reservoir, which raises the need to benchmark their results. The physical behavior models of polymer and surfactant were constructed and verified on a 1D scale reservoir model and further verified in a 3D model. Finally, simulations were conducted in a field-scale reservoir containing 680,400 grids, where results were compared and analyzed. The 1D and 3D model results suggest an excellent match between the different simulators in modeling surfactant–polymer floods. In the case of the field-scale model, the simulators matched in terms of oil recovery and total volumes produced and injected, while having similar reservoir pressure profiles but with significant discrepancies in terms of injected and produced chemicals. These results indicate that despite the differences in the calculated injected and produced chemicals due to the different models in the simulators, the effect of surfactant–polymer floods on oil recovery, total injected and produced fluids, and average pressure profiles can be comparably modeled in all of the three simulators.

Phase behavior and structure of a biocompatible microemulsion based on Tween 20, 2-ethylhexylglycerine and isopropyl palmitate in water

Microemulsions are thermodynamically stable mixtures of water and oil. For many applications, such as in cosmetics, it is important that the components are biocompatible. For the formulation of a new biocompatible microemulsion based on Tween 20 (Tw20) surfactant, the glycerol ether 2-ethylhexylglycerin (EHG) is employed as an alternative to commonly used short- to medium chain alcohols as cosurfactant. Tw20 itself is not capable of any significant solubilization but the addition of EHG allows to enhance the solubilization capacity for the polar oil isopropyl palmitate (IPP) largely. At a Tw20 to EHG molar ratio of 1:12, i.e., very large excess of cosurfactant, the solubilization capacity is increased by nearly three orders of magnitude compared to a pure Tw20 solution. The resulting oil-in-water (O/W) microemulsion is studied using static and dynamic light scattering (SLS/DLS) and small-angle neutron scattering (SANS). The SANS spectra are analyzed with a core–shell ellipsoid model, which indicates formation of oblate droplets at higher EHG content. Dynamic light scattering experiments confirm the presence of microemulsion droplets with hydrodynamic radii increasing from 3.8 to 19.8 nm upon addition of cosurfactant. In summary, this study shows that EHG is a cosurfactant that enhances the solubilization properties of a biocompatible surfactant largely and thereby renders it very useful for formulations.

Microemulsion phase behavior of live crude oil and revisiting the EACN framework for crude oils

Determination of the EACN of dead, surrogate, and live crude oils are revisited. The main objective of the study was to better understand the EACN of crude oil systems and to find more desirable practices in terms of approximation of crude oils. Microemulsion phase behaviors were measured in a wide range of oil compositions while keeping all formulation variables fixed except the oil. Pure hydrocarbons were used as oil phases or diluents to investigate the effect of nonideal mixing between crude oil and diluents. A synthetic live crude oil was constituted by adding 39.5 mol% of methane to a dead crude oil and then microemulsion phase behavior was investigated to determine the optimum salinity and solubilization ratios at 172 bar (2500 psi) and 90 °C. The results were analyzed based on two existing approaches in EACN framework, i.e., pure n-alkane trends against EACN versus dilution curves against EACN. The method using crude oil dilution curve results in a greater EACN of the crude oil by 2 units than by the method utilizing the pure n-alkane trend as a basis. The apparent EACN of methane was found to be much greater than its alkane carbon number of 9.3 based on the pure n-alkane trend and 11.6 based on the crude oil dilution method, respectively. Through systematic construction and investigation of optimum salinity vs. EACN curves, desirable practices to determine EACN of crude oils are presented. The results could be useful to approximate live crude oil EACN by designing more representative surrogate crude oils.

Microemulsion phase behavior of active live oil

Microemulsion phase behavior of live crude oil has been investigated at 1700 psi and 55 °C using an active crude oil with a total acid number of 1.18 mg-KOH/g-oil. The live crude oil was reconstituted by adding 36.0 mol% methane to dead crude oil. Sodium carbonate was used for a salinity scan, and also as an alkali to convert the acid components in crude oil to natural soap. The equivalent alkane carbon number (EACN) of dead crude oil was determined by measuring optimum salinity of dead crude oil and several surrogate crude oils diluted with pure n-alkanes. The optimum salinity of live crude oil was compared to those of dead and surrogate crude oils to determine the EACN of the live crude oil. To keep the surfactant pseudo-phase composition constant in the ternary phase diagram, the molar ratio of crude oil to synthetic surfactant was controlled. The natural soap and synthetic surfactant were kept the same for each volume ratio of crude oil to surfactant solution. The EACN of the crude oil was found to be independent of the soap-to-surfactant molar ratio, which means EACN is an intrinsic property of oil under the experimental conditions investigated. Based on the optimum salinity shift from dead crude oil to live crude oil, the compositional effect of methane with active crude oil was measured to be about the same as for inactive crude oil. The apparent EACN of methane was found to be equal to about 10.2. The solubilization ratio of the live oil at optimum salinity was greater than the value for the dead crude oil. The results indicate that the microemulsion phase behavior of live crude oil with acidic components can be interpreted using classical EACN concepts by the same criteria as that of inactive crude oil. Thus, the effect of the soap generation reaction can be decoupled from the physical interactions.

Investigation of Nanostructure and Interactions in Water-in-Xylene Microemulsions Using Small-Angle X-ray and Neutron Scattering.

The ability to modulate the size, the nanostructure, and the macroscopic properties of water-in-oil microemulsions is useful for a variety of technological scenarios. To date, diverse structures of water-in-alkane microemulsions stabilized by sodium bis(2-ethylhexyl) sulfosuccinate (AOT) have been extensively studied. Even though the decisive parameter which dictates the phase behavior of micremulsions is the nature of the continuous phase, relatively very few reports are available on the structure and interactions in the microemulsions of aromatic oil. Here, we present a fundamental investigation on water-in-xylene microemulsions using small-angle neutron scattering (SANS) at a fixed molar ratio (ω) of water to AOT. We elucidate the microstructural changes in the water-AOT-xylene ternary system at dilute volume fractions (Φ = 0.005, 0.01, 0.03), where the droplet-droplet interactions are absent, to moderately concentrated systems (Φ = 0.05, 0.10, 0.15, and 0.20), where colloidal interactions become important. We also characterize the reverse microemulsions (RMs) for thermally induced microstructural changes at six different temperatures from 20 to 50 °C. Depending on the magnitude of Φ, the scattering data is found to be well described by considering the RMs as a dispersion of droplets (with a Schulz polydispersity) which interact as sticky hard spheres. We show that while the droplet diameter remains almost constant with increase in the volume fraction, the attractive interactions become prominent, much like the trends observed for water-in-alkane microemulsions. With increase in temperature, the RMs showed a marginal decrease in the droplet size but no pronounced dependence on the interactions was observed with the overall structure remaining intact. The fundamental study on a model system presented in this work is key to understanding the phase behavior of multiple component microemulsions as well as their design for applications at higher temperatures, where the structure of most RMs breaks down.

A new surfactant wettability alteration model for reservoir simulators

AbstractSurfactants enhance oil recovery in naturally‐fractured oil‐wet rocks by wettability alteration and interfacial tension reduction. The oil‐wet state is ascribed to the adsorption of soap on the rock surface. Soaps are the dissociated forms of carboxylic acids in the crude oil, that is, carboxylate surfactants. This paper describes a new mechanistic surfactant wettability alteration model that was developed for and implemented in a reservoir simulator. The model captures the geochemical reactions of acid/soap, the formation of mixed micelles, Henry's law adsorption, and the formation of cationic surfactant‐anionic soap ion‐pairs. A new wettability scaling factor is used to interpolate between the oil‐wet and water‐wet relative permeability and capillary pressure curves. The new model also accounts for the effect of salinity and pH, so it should also be useful for modeling low‐salinity flooding without surfactant. Previous surfactant wettability alteration models ignored the underlying mechanisms and were not predictive. Simulations of both static and dynamic imbibition were performed to better understand the key surfactant parameters and the dynamics of wettability alteration, microemulsion phase behavior, and interfacial tension reduction on oil recovery. Optimizing surfactant formulations for wettability alteration is discussed.

Experimental investigation of hydrophobic and hydrophilic silica nanoparticles on extended surfactant properties: Micro-emulsion, viscosity, and adsorption behaviors

The novel applications of nanoparticles and surfactants are of interest for improving chemical oil recovery performance. In this study, two types of hydrophobic and hydrophilic SiO2 nanoparticles (NPs) were used in conjunction with a binary surfactant system (extended Carboxylate and Dioctyl sulfosuccinate (AOT) surfactants at the ratio of 0.6:0.4 by volume). An extensive series of experiments were performed in the presence of API brine containing NaCl: CaCl2 at the 8:2 wt ratio to study microemulsion phase behavior, interfacial tension (IFT), surfactant adsorption onto NP surfaces, solution and microemulsion viscosity, and oil recovery. The results indicate that the microemulsion phase behavior, optimum salinity (S*), and IFT were influenced by the concentrations and surface characteristics of the NPs. Hydrophobic or hydrophilic NPs at 500 ppm in the binary surfactant system could form Type III microemulsion and decrease the S* from 2 to 1.75 wt%. When the NP concentration reached 1000 ppm, the S* reduced to 1.5 wt%. The IFT value of the neat binary surfactant system at the S* was obtained in an ultralow range (0.0013 mN/m), and the IFT value of the hydrophobic NPs exhibited a more significant reduction than the hydrophilic NP systems. The adsorption result demonstrates that Carboxylate surfactant had lower adsorption onto hydrophilic NP than AOT. COSMO σ-profile and screened charge density illustrated that the low coverage of Carboxylate surfactant was from hydrogen bonding interaction, making the surfactant lie flat on the surface. The viscosity of the NP-surfactant solution was affected by the capacity of the surfactant adsorption onto the NP surface. In this regard, adding the hydrophobic NPs at 1000 ppm provided the highest solution viscosity over the entire shear rate and temperature range. The viscosity of the microemulsion formulated by hydrophobic NPs was higher than that of the microemulsion formulated by the hydrophilic NPs. The system with the lower NP concentration had higher microemulsion viscosity than the system with the higher NP concentration. The oil recovery results indicate that the appropriate NP type and concentration in the surfactant system could increase the displacing viscosity and decrease the microemulsion viscosity compared with the neat surfactant flooding system. The success in improving oil recovery was achieved with recovery efficiency of 88% original oil in place (OOIP).

Review: Implementing the hydrophilic–lipophilic deviation model when formulating detergents and other surfactant‐related applications

AbstractWhen designing surfactant formulations using ionic and nonionic surfactants, the hydrophile lipophile balance (HLB) is a generalized surfactant characterization parameter that has shown to be useful when designing surfactant formulations, in the case of both ionic and nonionic surfactants (Davies' and Griffin's methods). Microemulsion phase behavior studies have been extensively used to optimize surfactant formulations, but these studies can cover a very wide phase space and can often encounter troublesome non‐equilibrium issues such as coacervation. Detailed phase behavior studies can be time‐consuming and difficult to apply beyond the specific surfactant‐oil system studied. The hydrophilic–lipophilic deviation (HLD) provides a method to help expedite surfactant formulation research by reducing the number of phase behavior studies required to optimize a given formulation. Detergency experiments have indicated that there is an optimal range of HLD for a given fabric surface. This appears to apply to other applications, as well, for example, surfactant formulations used in enhanced oil recovery have been optimized using the HLD method. These studies found that the HLD can reflect total oil recovery, even if the surfactants were derived from different alcohol feedstocks (e.g., HLD of 0 would describe optimum conditions regardless the type of surfactant). Also with additional parameterization, the HLD method can also be applied to non‐ideal surfactant mixtures, specifically ionic/nonionic blends. Overall, the HLD framework has shown to be an effective screening tool for a wide range of surfactant‐related applications when appropriate experiments, assumptions, and understanding of surfactant and oil interactions are used to generate the HLD parameters.

Challenges in modeling microemulsion phase behavior

AbstractModeling the complex phase behavior of microemulsions has been the subject of research for decades for hydrocarbon oil and organic contaminant recoveries. The empirical Hand model has been the standard scheme for calculating phase behavior in reservoir simulators. On the other hand, the hydrophilic–lipophilic deviation (HLD) model in conjunction with the net curvature and average curvature models (HLD‐NAC) has provided some theoretical basis for modeling microemulsions. While the HLD‐NAC has been successful in describing salinity scans, only recently an HLD‐NAC approach was devised that could represent binodal curves with physical behavior, resulting in a succession of new microemulsion flash algorithms. While these new algorithms claimed to include the effects of cosolvent, there are only few works in the literature, which give an in‐depth description of the cosolvent modeling. Furthermore, to the best of our knowledge, no work has investigated the capability of HLD‐NAC models for predicting data for different cosolvent concentrations nor did any work present a comprehensive study of the application of HLD‐NAC against Hand model for formulations including cosolvents. This paper aims to contribute in filling such gap. We modify different versions of the new HLD‐NAC approach with physical binodal curves by providing more flexibility into controlling the binodal heights with the cosolvent concentration and investigate how well they can calibrate and predict data. Experimental data sets were considered here. The results suggest that some of the HLD‐NAC approaches produced negative solubilization ratios and the Hand model gave better predictions of the ternary diagram for extreme salinity values.

Modeling of High-Pressure and High-Temperature Microemulsion Experiments using HLD-NAC-Based Equation of State

Summary Surfactant flooding is a promising technique that can reduce interfacial tension (IFT) between oil and water to ultralow values, mobilizing previously trapped oil. For reservoirs at moderate to high pressures, understanding and modeling how pressure affects the phase behavior of a surfactant-brine-oil system is important to the design and implementation of an efficient/cost-effective surfactant flooding project. Typically, however, phase behavior experiments and models of that phase behavior are made only at low pressures. The main objective of this paper is to show how to model experimental data in a unified way for a large range of pressure, temperature, and other parameters, using hydrophilic-lipophilic deviation (HLD) and net-average curvature (NAC)-based equation-of-state (EOS). Pressure and temperature scans show that pressure has a significant effect on the surfactant microemulsion phase behavior, shifting it from an optimal three-phase system at low pressure to a nonoptimal two-phase system at high pressure. Further, multiple scans at different water/oil ratios (WORs) show a shift in the optimum indicating that phase behavior partitioning of the various components is changing with oil saturation. We obtained good fits of all experimental data including all two- and three-phase regions using a single tuned HLD-NAC EOS for a wide range of simultaneous variations in pressure, temperature, salinity, and overall composition. Such a simultaneous match and prediction by a single set of model parameters has never been done before. We also demonstrate the type of data needed for an accurate EOS. When input into a numerical simulator, the tuned EOS improves the predictions of the resulting phase behavior (size and shape of the two-phase lobes and three-phase regions) and IFTs with changing pressure, temperature, salinity, WORs, and surfactant/alcohol concentrations.

Study of the efficiency of technical grade nonionic surfactants

AbstractParameters concerning the microemulsion phase behavior of nonionic surfactants of the alkyl polyglycol ether type have extensively been investigated in the last years. By studying these, essential parameters for future applications can be determined. Especially in the field of enhanced oil recovery, lubricants, and cosmetic applications these parameters are of special interest. In this work, the influence of technical grade nonionic surfactants on the phase behavior and the resulting surfactant efficiency has been studied. For this, the alkyl chain length, the degree, type, and order of alkoxylation of the surfactant have been varied. The investigation of these parameters has been conducted by measuring the phase behavior via the Kahlweit fish diagram. It has been found that varying the C‐chain length has a great impact on the efficiency, whereas the influence of the ethoxylation degree is minor. By the introduction of propylene oxide, the efficiency has been improved significantly. Additionally, it is important to have the right order of alkoxylation. If the fatty alcohol is first ethoxylated and afterwards propoxylated the efficiency is significantly decreased.

Catanionic Surfactants for Improving Oil Production in Carbonate Reservoirs

Summary This paper presents the development of catanionic surfactants composed of cationic and anionic surfactants to make them high-performance products for chemical flooding in high-temperature and high-salinity carbonate reservoirs. The objective of this study is to optimize the surfactant chemistry by mixing oppositely charged anionic surfactants and cationic surfactants (CASs), which results in significant synergistic effects in interfacial properties due to electrostatic attraction to improve oil production at the given harsh conditions. The optimal mixing surfactant ratios were determined according to the brine-surfactant compatibility, microemulsion phase behavior, and the interfacial tension (IFT) between oil and surfactant solutions in high-salinity brine at 90°C. Comprehensive performance of the catanionic surfactants was evaluated, including adsorption of the surfactants onto the carbonate rocks and the long-term stability at 95°C. The coreflooding displacement experiments were performed using carbonate core plugs at 95°C to evaluate the potential of the optimal catanionic surfactant in improving oil recovery. Three catanionic surfactants with good compatibility were developed in this study. It appeared that the synergistic effect between the mixing surfactants was enhanced with increasing temperature. Although the IFT of the individual surfactants with crude oil was between 10−1 and 100 mN/m, a significant IFT reduction in the magnitude of 10−2 to 10−3 mN/m was observed by mixing the selected anionic surfactants and CASs. A salinity scan showed that the IFT values maintained a value of 10−2 mN/m in a wide salinity range, which demonstrated the effectiveness of the catanionic surfactant. In microemulsion phase behavior studies, the developed catanionic surfactant solution in the presence of crude oil exhibited Winsor Type III emulsions. The static adsorption quantities of the catanionic surfactants were lower than the values of the individual surfactants. All these indicated the feasibility of catanionic surfactants for their applications in the harsh reservoir conditions. The results of coreflooding displacement tests demonstrated significant oil recovery improvement beyond waterflooding. This work provides an efficient way to get surfactant formulations by mixing oppositely charged surfactants to obtain high performance in improving oil production under harsh conditions.

Prediction and programming of microemulsion phase behavior simulation

In the process of microemulsion flooding, microemulsion phase state may be affected by the adsorption of core and the distribution of oil and water, and the upper phase, the middle phase or the lower phase microemulsion will appear. Accurate description of microemulsion phase state and quantitative discrimination of equilibrium phase composition are of great theoretical value and research significance for the design of microemulsion flooding system and improving the recovery efficiency of microemulsion. Therefore, in this paper, microemulsion phase model is deeply studied. Aiming at the difficulty of solving the existing Hand model and the unknown parameters of the improved HLD-NAC model, we introduce the binodal curve range parameter D and the asymmetric migration degree parameter B, and establish a new phase behavior description method of the binodal curve, the two-phase plait point lines and the III-phase node line. Then the phase discrimination programming of microemulsion was carried out, and the change laws of phase number, phase type and mass fraction of equilibrium phases of any microemulsion system under different salinity were revealed. The results show that the simulation results of microemulsions accord with the salinity scanning law, and can accurately identify the complex microemulsion phase states.