Prediction of microemulsion phase behavior from surfactant and co-solvent structures

Structure-property models were developed to predict the optimum salinity, optimum solubilization ratio, and the aqueous stability limit from the molecular structures of surfactants and co-solvents used for enhanced oil recovery. The models are sufficiently accurate to provide a useful guide to experimental testing programs for the development of chemical formulations for enhanced oil recovery and other similar applications requiring low interfacial tension. This is the first time a structure-property model has been developed to predict the optimum solubilization ratio. The solubilization ratio can be used in the Huh equation to predict the interfacial tension, which is the most important property in enhanced oil recovery applications. The UTCEOR Database was constructed and used to develop the models. The database is a collection of highest-quality experimental chemical EOR data conducted at The University of Texas at Austin from 2005 to 2018. It contains several thousand phase behavior experiments using 34 unique crude oils, 294 unique surfactants, and 70 unique co-solvents. The structures of the surfactants and co-solvents were characterized and include variations in the type of hydrophobe (carbon number, degree of branching, polydispersity, and aromaticity), number of alkoxylate groups (propylene oxide and ethylene oxide), and the type of head group. The model focuses on blends of anionic surfactants and nonionic co-solvents. Both the optimum salinity and the optimum solubilization ratio were modeled as a function of monovalent and divalent cations in the brines. The oils were characterized using their equivalent alkane carbon number. The models include the effect of soaps generated from the neutralization of acidic crude oils. Previous models for optimum salinity have not included the effects of divalent cations, soap, and co-solvents among other limitations. Most importantly, the new model can be used to predict interfacial tension as well as optimum salinity whereas previous models were used to predict only optimum salinity. In this research, the structure-concentration and structure-property effect of co-solvents were modeled separately, whereas previous models convoluted both effects and were not predictive. New measurements were made and combined with literature data to develop improved correlations for the oil-water partition coefficient and the interface-water partition coefficient of co-solvents. These correlations were used with pseudophase theory to more accurately model the structure-concentration effect. A structure-property model was developed for the aqueous stability that predicts the coacervation of chemical formulations. The interactions between surfactant hydrophobes and the PO groups were modeled because they influence the stability of micelles. The effects of co-solvent, polymer, and divalent cations were included for the first time. The structure-property models can be used to predict formulations for a given oil, brine and temperature that are likely to achieve ultra-low IFT with aqueous stability at optimum salinity and thus greatly accelerate the process of finding the best formulations to test for chemical EOR.Petroleum and Geosystems Engineerin

HLD-NAC Based Solutions for Surfactant Flooding

Established technologies like primary recovery methods using gas pressure and other natural forces in the reservoir, and secondary recovery by water flooding can only approximately recover one-third of the crude oil present in known reservoirs. The overall recovery of a reservoir is a product of microscopic displacement efficiency, ED, and macroscopic displacement efficiency, EV,. In equation form, E=E_D E_V (1) ED measures the effective ness of the displacing fluid in mobilizing the oil at the pore scale. In water flooding reservoirs, ED is usually around 0.6-0.7, which means the residual oil saturation, Sor, in the regions contacted by the displacing water is 0.3-0.4. The primary reason for this high residual oil saturation is the capillary trapping at the pore throat, since in most sandstone reservoir water is the wetting phase. Researchers have recognized that a dimensionless capillary number N_c=μν/σ controlled the residual oil saturation, where ν is the interstitial velocity, μ is the viscosity of aqueous solution and σ is the oil-water interfacial tension (IFT) (Taber 1969; Stegemeier 1977; Melrose 1974; Foster 1973). Correlations between residual oil saturation and capillary number find as the capillary number increases to 10-2 magnitude, residual oil saturation can be reduced to lower than 0.05 (Abrams 1975). Surfactant is such a chemical that is added into aqueous solution to reduce oil-water IFT, hence increase the capillary number. Surfactant flood processes have been well developed in the past decades. Various new surfactants and formulations were invented and tailored to fit the reservoir of interest. The general procedures of a surfactant flooding project is shown in Figure 1-1. A candidate reservoir suitable for surfactant flooding is firstly screened. And formulation is designed according to the reservoir conditions at lab. Considered reservoir conditions include brine salinity, reservoir temperature and oil properties. Then coreflood is conducted to evaluate the displacement efficiency of the designed formulation. In next step, coreflood simulation is performed to explain the coreflood results and obtain parameters that can capture the multiphase displacement process. These parameters are then used as input in pilot test simulation to predict the oil recovery in field scale, hence the economics can be evaluated. Figure 1-1 Procedures of a surfactant flooding project In these procedures, microemulsion phase behavior plays a critical role. During formulation design, microemulsion phase behavior tests are conducted to screen candidate surfactant and optimize the surfactant formulation, which is time consuming and highly dependent on the experiences of formulation researchers. And in coreflood process, different microemulsion type corresponds to different displacement mechanism. Moreover, it is Type III microemulsion that most efficient in reducing oil-water IFT and mobilized trapped oil. In compositional surfactant flooding simulators, microemulsion phase behavior model is an important package to calculate phase composition, phase saturation and interfacial tension, etc. Therefore, an incorrect phase behavior model or improper input will lead to an unreliable simulation results. This work aims to provide solutions to these problems in surfactant flooding technology, by using a novel hydrophilic-lipophilic deviation (HLD) and net-average curvature (NAC) called thereafter HLD-NAC equation of state. In this dissertation, Chapters 2 and 3 focus on microemulsion modeling. Chapter 2 validated the HLD-NAC model for surfactant/brine/crude oil systems. Microemulsion phase behavior of various formulations were reproduced by using only one fitting parameter, the surfactant tail length L. The contribution has appeared in the Journal of Petroleum Science and Engineering. Chapter 3 further evaluated the predictability of the HLD-NAC equation of state. Without using any matching parameter, four optimum formulations and corresponding microemulsion phase behavior are predicted with the HLD-NAC model using laboratory characterized parameters as input. This contribution has been accepted in 2016 SPE Improved Oil Recovery Symposium and been submitted to SPE Journal for peer review. Chapters 4 and 5 combine the HLD-NAC model with numerical and analytical methods to study its advantages in modeling surfactant flooding. In Chapter 4, a new chemical flooding simulator is developed by implementing the HLD-NAC EOS into UTCHEM. An algorithm is invented to describe composition distribution on a ternary phase diagram using surfactant, water and oil as the pseudo-component. As a replacement of Hand’s rule phase behavior model in UTCHEM, the HLD-NAC EOS shows various advantages in both physical significance and computational efficiency. Chapter 5 attempts to analytically study three-component, two-phase surfactant flooding by coupling the HLD-NAC EOS and coherent theory. The analytical solution is compared with the results from numerical simulator developed in Chapter 4, to prove that the algorithm is correctly implemented into UTCHEM. Using the analytical solution, the effects of phase behavior dependent parameters on surfactant flooding can by systemically studied. Finally, Chapter 6 presents some concluding remarks of this work and recommendations for the future studies

UNDERSTANDING SPECIFIC ION EFFECTS AND INTERFACIALLY ACTIVE SOLUTES USING THE COLLIGATIVE PROPERTIES OF MICROEMULSIONS

Designing and optimizing surfactant formulations continues to be of great interest to many industrial endeavors. Many of these applications utilize an assortment of ingredients including electrolytes, alcohols and other interfacially active solutes. Using the Hydrophilic Lipophilic Deviation (HLD), and specifically Type III microemulsion structures, changes to amphiphilic behavior can be quantified. This study highlights the use of HLD parameters in predicting optimal formulations as well as approximating unknown surfactants using specific molar ratios of the binary surfactants. Mixtures of heterogeneous surfactants were evaluated and the nonideality determined, where the highest deviation was found using anionic-nonionic solutions. Further, the structure of the amphiphiles were considered using their respective HLD parameters, providing evidence that the K value relates to the lipophile length and may be observed in changes in surfactant solubility. Cc values were found to be analogous to HLB values and empirical regressions were provided for quick approximation. This work considered the colligative properties of microemulsions to address the effects of additional solutes to amphiphilic behavior. It was demonstrated that specific cations as well as interfacially active solutes like alcohols are able to shift surfactant HLD parameters as well as the microemulsion properties such as the solubilization parameter. A proposed colligative hydration model was successfully implemented, providing better predictions of optimum salinities for chloride salts for anionic amphiphiles than what is found in literature. The use of nonionic reference surfactant suggests the specific ion effects behave similarly towards an uncharged molecule as the colligative hydration numbers, hC, remained consistent. This approach was extended to alcohols where the hc values qualitatively agreed with the alcohol’s hydrodesimic numbers, hD, found through freezing point depressions. The general trend of increasing the alcohol alkyl length was observed, decreasing the alcohol's ability to interact with free interfacial water as it tends to partition further into the surfactant palisade layer. Ultimately the colligative approach provided evidence that the additive properties of polar solutes appear within the changes in amphiphilic behavior and can be utilized properly to return HLD to a colligative equation. Such an approach should be widely beneficial as formulators now can quickly screen and predict optimum formulations by simply using common additive properties of solutes such as size, valency, and hydration

How to Attain an Ultralow Interfacial Tension and a Three‐Phase Behavior with a Surfactant Formulation for Enhanced Oil Recovery: A Review. Part 2. Performance Improvement Trends from Winsor's Premise to Currently Proposed Inter‐ and Intra‐Molecular Mixtures

The minimum interfacial tension occurrence along a formulation scan at the so-called optimum formulation is discussed to be related to the interfacial curvature. The attained minimum tension is inversely proportional to the domain size of the bicontinuous microemulsion and to the interfacial layer rigidity, but no accurate prediction is available. The data from a very simple ternary system made of pure products accurately follows the correlation for optimum formulation, and exhibit a linear relationship between the performance index as the logarithm of the minimum tension at optimum, and the formulation variables. This relation is probably too simple when the number of variables is increased as in practical cases. The review of published data for more realistic systems proposed for enhanced oil recovery over the past 30 years indicates a general guidelines following Winsor’s basic studies concerning the surfactant–oil–water interfacial interactions. It is well known that the major performance benefits are achieved by blending amphiphilic species at the interface as intermolecular or intramolecular mixtures, sometimes in extremely complex formulations. The complexity is such that a good knowledge of the possible trends and an experienced practical know-how to avoid trial and error are important for the practitioner in enhanced oil recovery

Current Research and Challenges in Bitumen Emulsion Manufacturing and Its Properties

Gefördert durch den Publikationsfonds der Universität Kasse

CARBONACEOUS NANOSIZED SURFACTANT CARRIERS AND OIL-INDUCED VISCOELASTIC FLUID FOR POTENTIAL EOR APPLICATIONS

This dissertation aims to advance the conventional tertiary oil recovery method, surfactant flooding process. Via injecting a finite slug of surfactant-only or mixture of surfactant/polymer solution into reservoir, surfactants are capable to dramatically reduce the residual oil/water interfacial tension (IFT) thus mobilize trapped oil. Despite the technical viability of surfactant flooding, this approach has some difficulties to be realized at large field scale, such as substantial adsorption loss, and unfavorable sweep efficiency of surfactant-only slug. This dissertation examined the feasibility of using carbonaceous nanoparticles, multiwalled carbon nanotube (MWNT), and carbon black as potential surfactant carriers in enhanced oil recovery. Stability of MWNT dispersion at high temperature high salinity levels, typical encountered in reservoir, as well as transport and fate of these stable nano-fluids in porous medium were first examined as a prerequisite for any field applications. MWNTs exhibited exceptional stability in 10 wt% brine by dispersing them with nonionic surfactant such as alkylphenol polyethoxylates with a large number of ethylene oxide (EO) groups. In the sandpack column test, a binary surfactant formulation, which consisted of a nonionic surfactant and an anionic surfactant in the proper ratios, exhibited an excellent capability to propagate MWNT, with 96% of the injected nanotubes recovered in the effluent. Chapter 2 presents the details of MWNT stability and transport in porous medium, which was previously published on Energy & Fuels. A successful surfactant delivery agent requires that surfactant ought to be released from the carriers once contact the target oil. In Chapter 3, batch adsorption tests indicated that competitive adsorption of surfactant on nanoparticles was beneficial to decrease adsorptive loss on Ottawa sand at equilibrium concentration below critical micelle concentration; microemulsions phase behavior proved spontaneous release of loaded surfactants from the treated MWNTs surfaces to oil/water interface; sand pack column tests carried out for an optimum surfactant formulation affirmed the advantage of adding nanoparticles into surfactant slug, as injection of MWNT-surfactant blend achieved faster and higher tertiary recovery than surfactant-only formulation. Chapter 3 was previously published on Fuel. An episode in the research of stable carbonaceous nanoparticles dispersion, reversed binary micellar interactions between anionic surfactant alpha olefin sulfonate (AOS) and nonionic surfactant nonylphenol polyethylene glycol ether (NPEs) were observed depending on the addition of electrolytes. In the absence of additional electrolytes, NPEs exhibited substantially higher activity in micelles than bulk solution; with growth of EO groups, shrinkage on the scale of synergistic interaction was evidenced. In contrary, with swamping amount of electrolytes, synergistic interactions enlarged with the rise of EO groups, and AOS activity in mixed micelles was found depending on both EO length and bulk mole fraction 〖(α〗_A). These findings are summarized in Chapter 4 and have been published on Colloids and Surfaces A: Physicochemical and Engineering Aspects. Chapter 5 discovered an oil-induced viscoelastic wormlike micellar solution. Wormlike micellar solution blends are important for industrial products where the high viscosity and elastic properties are exploited. However, wormlike surfactant micelles are extremely susceptible to oils; solubilization of paraffinic oils inside the micelle core leads to a disruption of wormlike micelles and loss of viscoelasticity. Oil-induced viscoelastic micellar fluid system is promising for various reservoir applications, such as proppant carrying fluids in hydraulic fracturing, and chemical slugs with built-in viscosity control in enhanced oil recovery. Chapter 6 presents some concluding remarks of this work and recommendations for the future studies

Development of a Novel, Microemulsion System for the Simultaneous Delivery of Hydrophilic and Hydrophobic Active Pharmaceutical Ingredients (APIs)

Concurrent chronic disease and ensuing multi-morbidity are a debilitating reality for millions of Canadians. This adversity is compounded by increased pill burden and decreased patient adherence. Microemulsions (MEs) serve as a potential multi-drug therapy solution. MEs are thermodynamically stable, colloidal systems whose oil and water compositions and nano-sized droplets have the potential to facilitate simultaneous hydrophilic and lipophilic drug delivery, while improving bioavailability. However, the area of multi-drug delivery using ME technology is largely unexplored and unfulfilled. In order to develop a ME capable of simultaneous multi-drug delivery, emulsifying agents as the heart of these systems must be investigated. In this work, the potential for multi-drug delivery using ME systems was explored with a particular focus on emulsifying agent properties conducive to this purpose. A prenatal supplement comprised of eleven active pharmaceutical ingredients (APIs) of varying hydro- and lipophilicity was selected as a proof of concept. Five non-ionic surfactants were subjected to extensive ternary phase diagram (TPD) mapping with a medium chain triglyceride, Miglyol 812 in order to identify regions of monophasic microemulsion formation. Optimization was performed via critical micelle concentration determination and the hydrophilic-lipophilic deviation (HLD) equation. A final microemulsion comprised of 3:1 Polysorbate 80:Cremophor RH 40 surfactant, Miglyol 812 and water in a surfactant:oil:water (S:O:W) ratio of 50:40:10, was identified as optimal for monophasic, microemulsion formation. Eleven active pharmaceutical ingredients- five lipophilic (Vitamins A, D, E, K and docosahexaenoic acid) and six hydrophilic (Vitamins B1, B2, B3, B6, B9, B12) were then successfully incorporated. The resulting microemulsion was determined to be of a bicontinuous nature and after 100x aqueous dilution, spherical droplets were identified via TEM with a diameter of 164 ± 37 nm, a charge of -14.1 ± 2.2 mV and a low viscosity of 1.04 ± 0.04 mPa/s. Twelve additional non-ionic surfactants were screened for possible use in the formulation. Polysorbate 81, with 15 less ethylene oxide head groups but equivalent carbon chain length to Polysorbate 80, was identified as most promising based on droplet diameter and zeta potential. Thus, this type of multi-drug formulation appeared to be tolerable to larger changes in non-ionic surfactant head group than hydrocarbon chain length; Hydrophilic-lipophilic balance (HLB), in contrast, appeared to have little to no effect. Two additional drug-loaded microemulsion formulations comprised of 3:1 Polysorbate 81:Cremophor RH 40 surfactant, Miglyol 812 oil and water in S:O:W ratios of 40:50:10 and 50:40:10, resulted in droplet diameters of 94 ± 15 nm and 81 ± 2.4 nm, and zeta potential values of -17 ± 4 mV and -23 ± 6 mV, respectively after 100x aqueous dilution. All final multi-drug loaded MEs demonstrated >70% dissolution improvement of folic acid and >90% dissolution improvement of riboflavin in 50 mM phosphate buffer (pH 7.4) as compared to a commercial prenatal supplement in suspension form. Overall, it was demonstrated that the process of TPD mapping, HLD optimization and careful surfactant screening was instrumental in the successful development of a multi-drug microemulsion system with the potential to treat concurrent, chronic diseases in a single dose