Synthesis of an Alkyl Polyoxyethylene Ether Sulfonate Surfactant and Its Application in Surfactant Flooding

Surfactant flooding as a potential enhanced oil‐recovery technology in a high‐temperature and high‐salinity oil reservoir after water flooding has attracted extensive attention. In this study, the synthesis of an alkyl alcohol polyoxyethylene ether sulfonate surfactant (C₁₂EO₇S) with dodecyl alcohol polyoxyethylene ether and sodium 2‐chloroethanesulfonate monohydrate, and its adaptability in surfactant flooding were investigated. The fundamental parameters of C₁₂EO₇S were obtained via surface tension measurement. And the ability to reduce oil–water interfacial tension (IFT), wettability alteration, emulsification, and adsorption was determined. The results illustrated that IFT could be reduced to 10^?3 mN m^?1 at high temperature and high salinity without additional additives, and C₁₂EO₇S exhibited benign wettability alternate ability, and emulsifying ability. Furthermore, the oil‐displacement experiments showed that C₁₂EO₇S solution could remarkably enhance oil recovery by 16.19% without adding any additives.     

Synthesis,Characterization and Properties of <Emphasis Type="Italic">N</Emphasis>-Alkyl-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-di(2-hydroxyethyl) Amine Oxides

N‐Dodecyl‐N,N‐di(2‐hydroxyethyl) amine oxide (C₁₂DHEAO) and N‐stearyl‐N,N‐di(2‐hydroxyethyl) amine oxide (C₁₈DHEAO) were synthesized with N‐alkyl‐diethanolamine and hydrogen peroxide. Their chemical structures were confirmed using ¹H‐NMR spectra, mass spectral fragmentation and FTIR spectroscopic analysis. It was found that C₁₂DHEAO and C₁₈DHEAO reduced the surface tension of water to a minimum value of approximately 28.75 mN m^?1 at concentration of 2.48 × 10^?3 mol L^?1 and 32.45 mN m^?1 at concentration of 5.21 × 10^?5 mol L^?1, respectively. The minimum interfacial tension (IFT_min) and the dynamic interfacial tension (DIT) of oil–water system were measured. When C₁₈DHEAO concentration was in the range of 0.1–0.5%, the IFT_min between liquid paraffin and C₁₈DHEAO solutions all reached the ultra‐low interfacial tension. Furthermore, their foam properties were investigated by Ross‐Miles method, and the height of foam of C₁₂DHEAO was 183 mm. It was also found that they showed strong emulsifying power.     

Interfacial properties of cationic and anionic Gemini surfactant mixtures

The possibility and the prospect of cationic/anionic (“catanionic”) surfactant mixtures based on sulfonate Gemini surfactant (SGS) and bisquaternary ammonium salt (BQAS) in the field of enhanced oil recovery was investigated. The critical micelle concentration (CMC) of SGS/BQAS surfactant mixtures was 5.0 × 10⁻⁶ mol/L, 1–2 orders of magnitude lower than neat BQAS or SGS. A solution of either neat SGS or BQAS, could not reach an ultra-low interfacial tension (IFT); but 1:1 mol/mol mixtures of SGS/BQAS reduced the IFT to 1.0 × 10⁻³ mN/m at 100 mg/L. For the studied surfactant concentrations, all mixtures exhibited the lowest IFT when the molar fraction of SGS among the surfactant equaled 0.5, indicating optimal conditions for interfacial activity. The IFT between the 1:1 mol/mol SGS/BQAS mixtures and crude oil decreased and then increased with the NaCl and CaCl₂ concentrations. When the total surfactant concentration was above 50 mg/L, the IFT of SGS/BQAS mixtures was below 0.01 mN/m at the studied NaCl concentrations. Adding inorganic salt reduced the charges of hydrophilic head groups, thereby making the interfacial arrangement more compact. At the NaCl concentration was above 40,000 mg/L, surfactant molecules moved from the liquid–liquid interface to the oil phase, thus resulting in low interfacial activity. In addition, inorganic salts decreased the attractive interactions of the SGS/BQAS micelles that form in water, decreasing the apparent hydrodynamic radius (D_{H, app}) of surfactant aggregates. When the total concentration of surfactants was above 50 mg/L, the IFT between the SGS/BQAS mixtures and crude oil decreased first and then increased with time. At different surfactant concentrations, the IFT of the SGS/BQAS mixtures attained the lowest values at different times. A high surfactant concentration helped surfactant molecules diffuse from the water phase to the interfacial layer, rapidly reducing the IFT. In conclusion, the cationic-anionic Gemini surfactant mixtures exhibit superior interfacial activity, which may promote the application of Gemini surfactant.     

Novel fluorinated surfactants for enhanced oil recovery in carbonate reservoirs

Novel surfactant‐polymer (SP) formulations containing fluorinated amphoteric surfactant (surfactant‐A) and fluorinated anionic surfactant (surfactant‐B) with partially hydrolyzed polyacrylamide (HPAM) were evaluated for enhanced oil recovery applications in carbonate reservoirs. Thermal stability, rheological properties, interfacial tension, and adsorption on the mineral surface were measured. The effects of the surfactant type, surfactant concentration, temperature, and salinity on the rheological properties of the SP systems were examined. Both surfactants were found to be thermally stable at a high temperature (90 °C). Surfactant‐B decreased the viscosity and the storage modulus of the HPAM. Surfactant‐A had no influence on the rheological properties of the HPAM. Surfactant‐A showed complete solubility and thermal stability in seawater at 90 °C. Only surfactant‐A was used in adsorption, interfacial tension, and core flooding experiments, since surfactant‐B was not completely soluble in seawater and therefore was limited to deionized water. A decrease in oil/water interfacial tension (IFT) of almost one order of magnitude was observed when adding surfactant‐A. However, betaine‐based co‐surfactant reduced the IFT to 10^?3 mN/m. An adsorption isotherm showed that the maximum adsorption of surfactant‐A was 1 mg per g of rock. Core flooding experiments showed 42 % additional oil recovery using 2.5 g/L (2500 ppm) HPAM and 0.001 g/g (0.1 mass%) amphoteric surfactant at 90 °C.     

Effects of Divalent Salts on the Interfacial Activity of the Mixed Surfactants at the Water/Model Oil Interface

In our previous report, the mixed cationic/anionic surfactant system consisting of N-dodecyl-N-methylpyrrolidinium bromide (L12) and sodium dodecyl sulfate (SDS) showed good interfacial tension (IFT) reduction of water/model oil (V_toluene:V _n-decane = 1:1). In the present study, the effects of divalent salts (MgCl₂ or CaCl₂) on the interfacial activity were systematically evaluated. The additional Mg²⁺ ions greatly reduced the IFT to an ultralow value, whereas Ca²⁺ ions caused the generation of the precipitates and resulted in increased IFT values. The precipitates disappeared in binary divalent salt solutions, and the IFT values remained at a low level. Based on the valence, polarizability, and hydrated radius of the ions, we proposed a model to explain the abnormal changes. The effects of NaCl and temperature were investigated to further verify our proposed mechanism. Moreover, the additional divalent salts obviously enhanced the stability of L12/SDS stabilized emulsions.     

Intrinsic viscosity,rheological property,and oil displacement of hydrophobically associating fluorinated polyacrylamide

The surface‐active polymer (FPAM) was synthesized by free‐radical polymerization of acrylamide (AM), 2‐acrylamido‐2‐methyl‐1‐propane sulfonic acid (AMPS) and N ‐dodecyl‐N ‐perfluoro octane sulfonyl acrylamide (AMPD), which was prior prepared by reacting dodecylamine, perfluoro‐1‐octanesulfonyl fluoride, and acryloyl chloride. Parameters affecting the intrinsic viscosity ([η]) and apparent viscosity (η) of FPAM, such as reaction temperature, AMPD concentration, AMPS concentration, monomer concentration, initiator concentration, and pH were examined. Apparent viscosity and interfacial tension (IFT) of FPAM solution were evaluated. Subsequently, temperature tolerance and shear tolerance were investigated by comparing with hydrolyzed polyacrylamide (HPAM), and results indicated that the FPAM displayed better performances than HPAM. FPAM can reduce the IFT between crude oil/water, and the IFT values are around at 2.91 and 3.9 mN m^?1 corresponding to FPAM and HPAM/FC‐118. The sandpack model oil displacement experiment showed that water flooding can further increase the oil recovery to 15.01% (FPAM), compared with 9.26% oil recovery for HPAM, and 10.99% oil recovery for HPAM/FC‐118. The glass micromodel techniques for studying enhanced oil recovery get a good result and provide a useful reference for understanding the displacement behaviors in polymer flood process. It could be concluded that the introduction of fluorinated groups in the polymer chain was helpful in enhancing the oil displacement efficiency. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134 , 44672.     

From Phase Behavior to Understand the Dominant Mechanism of Alkali-Surfactant-Polymer Flooding in Enhancing Heavy Oil Recovery

The primary objective of this work was to understand the dominant mechanism(s) of alkali‐surfactant‐polymer (ASP) flooding in enhancing heavy oil recovery. Chemical formulations were first optimized based on phase behavior studies. The data indicated that alkali and surfactant created a synergistic effect at the oil/water interface, which further decreased the interfacial tension (IFT) and improved the emulsification. However, it was also found that the addition of alkali was detrimental to the viscous properties of the chemical systems and caused the ultimate oil recovery to decrease. In other words, the macroscopic sweep efficiency as a result of viscosity was the primary factor determining the overall recovery of heavy oil followed by emulsification, which was verified by the phase behavior of the effluent. Based on the experimental results, we found that for this targeted heavy oil reservoir, surfactant‐polymer (SP) flooding was more appropriate than ASP flooding and it was not necessary to decrease the IFT to the ultralow level (10^?3 mN/m) using alkali. Through chemical flooding, the incremental oil recovery was increased up to 27% of original oil in place, indicating the potential of this technique in heavy oil reservoirs.     

A Zwitterionic Surfactant Bearing Unsaturated Tail for Enhanced Oil Recovery in High‐Temperature High‐Salinity Reservoirs

High‐temperature/high‐salinity (HTHS) reservoirs contain a significant fraction of the world's remaining oil in place and are potential candidates for enhanced oil recovery (EOR). Selection of suitable surfactants for such reservoirs is a challenging task. In this work, two synthesized zwitterionic surfactants bearing a saturated and an unsaturated tail, namely 3‐(N‐stearamidopropyl‐N,N‐dimethyl ammonium) propanesulfonate and 3‐(N‐oleamidopropyl‐N,N‐dimethyl ammonium) propanesulfonate, respectively, were evaluated. The surfactant with the unsaturated tail showed excellent solubility in synthetic seawater (57,643 ppm) and in formation brine (213,734 ppm). However, the unsaturated surfactant with a saturated tail showed poor solubility, and therefore it was not evaluated further. The thermal stability of the synthesized unsaturated surfactant solution in seawater was evaluated by heating the solution at 90 °C in a sealed aging tube for 2 weeks. The thermal stability of the unsaturated surfactant was confirmed by FTIR and NMR analysis of the aged samples at such harsh conditions. The critical micelle concentration (CMC) of the synthesized unsaturated surfactant in seawater was 1.02 × 10^?4 mol L^?1, while the surface tension at CMC was 30 mN m^?1. The synthesized unsaturated surfactant was able to reduce the oil–water interfacial tension to ~10^?1 mN m^?1 at different conditions. A commercial copolymer of acrylamide and 2‐acrylamido‐2‐methylpropane sulfonic acid (AM‐AMPS) was tested for EOR applications in HTHS conditions. The addition of the synthesized unsaturated surfactant to the AM‐AMPS copolymer increased the viscosity of the system. The increase in oil recovery by injecting the unsaturated surfactant solution and the surfactant–polymer mixture in solution was 8 and 21%, respectively. The excellent properties of the synthesized unsaturated surfactant show that surfactants with an unsaturated tail can be an excellent choice for HTHS reservoirs.     

Investigation of Interfacial Tension Reduction,Wettability Alteration,and Oil Recovery Using a New Non-ionic Oil-Based Surfactant from Gemini Surfactants Family Coupled with Low-Salinity Water: Experimental Study on Oil-Wet Carbonate Rock

Low-salinity surfactant (LSS) flooding is a combined enhanced oil recovery (EOR) technique that increases oil recovery (OR) by altering the rock surface wettability and reducing oil–water interfacial tension (IFT). In this study, optimum concentrations of several types of salt in distilled water were obtained on the basis of IFT experiments for the preparation of low-salinity water (LSW). Then, a new oil-based natural surfactant (Gemini surfactant, GS) was combined with LSW to investigate their effects on IFT, wettability, and OR. Experimental results showed that LSW is capable of reducing IFT and contact angle, but the synergy of GS and the active ions Mg²⁺, Ca²⁺, and SO₄²⁻ in LSW was more effective on IFT reduction and wettability alteration. The combination of 1000 ppm MgSO₄ and 3000 ppm GS led to a decrease in contact angle from 134.82° to 36.98° (oil-wet to water-wet). Based on core flooding tests, LSW injection can increase OR up to 71.46% (for LSW with 1000 ppm MgSO₄), while the combination of GS and LSW, as LSS flooding, can improve OR up to 84.23% (for LSS with 1000 ppm MgSO₄ and 3000 ppm GS). Therefore GS has great potential to be used as a surfactant for EOR.     

Preparation and Performance Evaluation of Fatty Amine Polyoxyethylene Ether Diethyl Disulfonate for Enhanced Oil Recovery in High‐Temperature and High‐Salinity Reservoirs

To enhance oil recovery in high‐temperature and high‐salinity reservoirs, a novel fatty amine polyoxyethylene ether diethyl disulfonate (FPDD) surfactant with excellent interfacial properties was synthesized. The interfacial tension (IFT) and contact angle at high temperature and high salinity were systematically investigated using an interface tension meter and a contact angle meter. According to the experimental results, the IFT between crude oil and high‐salinity brine water could reach an ultra‐low value of 10^?3 mN m^?1 without the aid of extra alkali at 90°C after aging. The FPDD surfactant has strong wettability alternation ability that shifts wettability from oil‐wet to water‐wet. The FPDD surfactant with a high concentration also has good emulsion ability under high‐temperature and high‐salinity conditions. Through this research work, we expect to fill the lack of surfactants for high‐temperature and high‐salinity reservoirs and broaden its great potential application area in enhanced oil recovery.     

Enhancing Oil Recovery by Low Concentration of Alkylaryl Sulfonate Surfactant without Ultralow Interfacial Tension

Surfactant flooding plays a critical role in chemically enhanced oil recovery over the last half century, with the widely accepted mechanism of ultralow interfacial tension (IFT) by forming middle-phase microemulsions with high concentration of a lead surfactant and a cosurfactant. However, it is found practically from field trials that high oil recovery efficiency can be obtained from low concentration surfactant flooding without forming microemulsions, and the principle behind has not been clearly unraveled yet. Here the solubilization of paraffin oil by the micelles formed with a commercial enhanced oil recovery surfactant, raw naphthenic arylsulfonates (NAS), was investigated using ultraviolet-visible (UV–Vis) spectroscopy, dynamic light scattering (DLS), and transmission electron microscopy (TEM). It is found that paraffin oil can be well solubilized inside the NAS micelles, and mainly localized in the hydrophobic core of the micelles. The solubilization capacity of NAS micelles increases with increasing its concentration, and the size of micelles increases, but morphology of the micelles remains spherical with increasing the amount of paraffin oil, along with an appearance transition from transparent to opaque until the maximum solubilization capacity is reached. Core flooding results with crude oil indicate that in the presence of 0.24 wt.% polymer, addition of 0.1, 0.2, 0.5, and 1.0 wt.% NAS can get oil recovery factor of 24.1%, 27.0%, 30.5%, and 38.3%, which increases linearly with increasing NAS concentration though with the interfacial tension values only in the magnitude of 10⁻² mN m⁻¹ level. These findings prove preliminarily micellar solubilization can help increasing oil recovery efficiency even without ultralow IFT.     

Characterizations of surfactant synthesized from Jatropha oil and its application in enhanced oil recovery

Surfactants are frequently used in chemical enhanced oil recovery (EOR) as it reduces the interfacial tension (IFT) to an ultra‐low value and also alter the wettability of oil‐wet rock, which are important mechanisms for EOR. However, most of the commercial surfactants used in chemical EOR are very expensive. In view of that an attempt has been made to synthesis an anionic surfactant from non‐edible Jatropha oil for its application in EOR. Synthesized surfactant was characterized by FTIR, NMR, dynamic light scattering, thermogravimeter analyser, FESEM, and EDX analysis. Thermal degradability study of the surfactant shows no significant loss till the conventional reservoir temperature. The ability of the surfactant for its use in chemical EOR has been tested by measuring its physicochemical properties, viz., reduction of surface tension, IFT and wettability alteration. The surfactant solution shows a surface tension value of 31.6 mN/m at its critical micelle concentration (CMC). An ultra‐low IFT of 0.0917 mN/m is obtained at CMC of surfactant solution, which is further reduced to 0.00108 mN/m at optimum salinity. The synthesized surfactant alters the oil‐wet quartz surface to water‐wet which favors enhanced recovery of oil. Flooding experiments were conducted with surfactant slugs with different concentrations. Encouraging results with additional recovery more than 25% of original oil in place above the conventional water flooding have been observed. © 2017 American Institute of Chemical Engineers AIChE J, 63: 2731–2741, 2017     

Synergy between Sugar-Based Anionic-Nonionic Surfactants and Ag-TiO2 Nanohybrids for Enhanced Oil Recovery

For improving the oil recovery performance, Ag-TiO₂ nanoparticles (NP) were added to the eco-friendly sugar-based anionic nonionic surfactant (GDA) solution, and the mixtures acted as the oil displacement agent. The synthesized GDA and Ag-TiO₂ were characterized using Fourier transform infrared spectrometry (FT-IR), ¹H nuclear magnetic resonance (¹H NMR), and X-ray diffraction (XRD). Changes in the zeta potential and transmission electron microscope (TEM) images of the mixtures confirmed their synergistic effects on the suspension stability. The relationships between surface tension, interfacial tension (IFT), three-phase contact angle, and emulsion and oil recovery efficiency were comprehensively investigated, both before and after Ag-TiO₂ NP addition. We concluded that the Ag-TiO₂/GDA mixtures could effectively alter the contact angle, decrease IFT, and form stable emulsions, thereby resulting in the enhancement of oil recovery. The core flooding conducted with the stabilized NP-surfactant (Ag-TiO₂ and GDA) fluid showed a marked improvement in oil recovery over 18%. This study provides additional options for using the synergistic effect of NP and surfactants for enhanced oil recovery.     

A Star-Shaped Anionic Surfactant: Synthesis,Alkalinity Resistance,Interfacial Tension and Emulsification Properties at the Crude Oil–Water Interface

In this research, a star‐shaped surfactant was synthesized through the chlorination reaction, alkylation reaction and sulfonation reaction of triethanolamine, which is composed of three hydrophobic chains and three sulfonate hydrophilic groups. The critical micelle concentration (CMC) of the surfactant was measured by the surface tension method, and the results showed that it had high surface activity with CMC of 5.53 × 10^?5 mol/L. The surfactant was superior in surface active properties to the reference surfactants SDBS and DADS‐C₁₂. The interfacial tension (IFT) of the studied crude oil–water system (surfactant concentration 0.1 g/L, NaOH concentration 0.5 g/L, and experimental temperature 50 °C) dropped to 1.1 × 10^?4 mN/m, which can fulfil the requirement of surfactants for oil displacement. An aqueous solution of the surfactant and crude oil was emulsified by shaking, which formed a highly stable oil‐in‐water (O/W) emulsion with particle size of 5–20 μm. The oil displacement effect was almost 12%.     

Application of pH-Responsive Viscoelastic Surfactant as Recyclable Fluid at High Temperature

A pH-responsive amphiphilic surfactant stearic amide 3-(N,N-dimethylamino)propylamide (SAA) was synthesized and served as a thickener in aqueous solution to construct a switchable viscoelastic surfactant fluid (VES fluid). The structure of SAA was studied by ¹H NMR, and the viscoelastic behavior of VES fluid was studied in detail by rheological measurements. The viscosity of this VES fluid can be switched reversibly from low to high immediately by adjusting system pH value. Even at high shear rate (170 s⁻¹) and high temperature (90 °C), excellent viscoelastic behavior of this VES fluid can be observed, which is a key performance for fracturing applications. Meanwhile, the recycled VES fluid can still maintain good pH-responsive behavior even after more than three cycles. These unique performances of this VES fluid not only enhanced our understanding of the transformation of wormlike micelles at high temperature, but also enriched a large potential of VES fracturing fluid in the development of oil and gas reservoirs.     

Simultaneous influence of uni-univalent salt aqueous solutions and sodium dodecyl sulfate surfactant on interfacial tension of toluene-water

The simultaneous influence of NaCl, KCl and KI salts and well known sodium dodecyl sulfate (SDS) surfactant on the interfacial tension (IFT) of conventionally used chemical system of toluene-water was studied. The concentration range of salts was within (0.010 to 0.075) mol/dm³ and of surfactant within (1.7 to 26.0)×10^?5 mol/dm³. SDS adsorption on interface is highly intensified in the presence of salts and IFT can reach to 67.1% of its initial value. Accordingly, the role of ions was investigated and the order of salts effectiveness was revealed as KI?KCl>NaCl. The obtained data, with both effects, were nicely reproduced using an equation of state, based on Gibbs adsorption equation and the Langmuir isotherm. Two relevant important adsorption parameters exhibited reasonable variations. Furthermore, the general revealed linear variation of IFT with a previously defined “effective concentration” indicates the strong influence of the surfactant counterions.     

Interactions of a smart cationic polyelectrolyte based on hydroxypropylcellulose with an anionic surfactant

Novel thermosensitive, cationic polyelectrolyte was obtained by grafting N‐vinylformamide onto hydroxypropylcellulose followed by the hydrolysis of the formamide groups to the amine groups. The effect of the ionic strength on the lower critical solution temperature of the polymers was studied. The interactions of the polymers with sodium dodecyl sulfate (SDS) as a model anionic surfactant were studied. It was found by the measurements of the light scattering and fluorescence spectroscopy that the graft copolymers obtained strongly interact with SDS with the formation of polymer‐surfactant complexes. The values of critical association concentration (cac) of these polymer‐surfactant systems were found to be of the order of 10^?5 mol/dm³ at pH = 6.5 and of the order of 10^?6 mol/dm³ at pH = 2.5. The polymer was shown to be potentially useful for the purification of water from anionic surfactants. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2008     

The Effects of Dynamic Noncovalent Interaction between Surfactants and Additional Salt on the pH-Switchable Interfacial Tension Variations

The dynamic noncovalent interaction between the anionic surfactant sodium dodecyl benzene sulfonate (SDBS) and 1,3-diphenylguanidine (DPG) was employed to control the interfacial activity of the surfactant. At high HCl concentration (1000 mg L⁻¹), the SDBS/DPGⁿ⁺ system could reduce the water/oil interfacial tension (IFT) to 10⁻⁴ mN m⁻¹ order of magnitude, which was much lower than the IFT values in the SDBS/DPG⁺ system with a low HCl concentration (100 mg L⁻¹) and the individual SDBS system by three and four orders of magnitude, respectively. The pH-switchable protonation of amido groups in DPG molecules determines the SDBS/DPG molecular interaction and the amplitude of IFT reduction, which was confirmed by control experiments using two other surfactants (sodium dodecyl sulfate [SDS] and dodecyl trimethylammonium bromide [DTAB]). Moreover, the investigation of the NaCl and temperature effects on the IFT indicated the intensity of mixed SDBS/DPGⁿ⁺ adsorption layers at the water/oil interface.     

Synthesis of <Emphasis Type="Italic">N</Emphasis>-(3-Oxapropanoxyl)dodecanamide and its Application in Surfactant-Polymer Flooding

Alkali-surfactant-polymer (ASP) flooding has been considered to be one of the useful tertiary oil recovery techniques. However, field tests in China have revealed that serious side effects may occur due to using alkali. Thus alkali-free SP flooding is more favorable in China. Unfortunately, surfactants effective in ASP flooding are usually ineffective in the absence of alkali and new surfactants need to be designed. In this paper N-(3-Oxapropanoxyl)dodecanamide as a pure compound and a mixture of homologues with narrow EO number distribution, synthesized by the reaction of lauroyl chloride with diglycolamine and addition of one ethylene oxide to coconut monoethanolamide respectively, are examined for their adaptability in SP flooding. It is found that, when mixed with betaines, both products can reduce Daqing crude oil/connate water interfacial tension to a magnitude of 10⁻³–10⁻⁴ mNm⁻¹ at 45 °C in a wide surfactant concentration range, 0.01–0.5 wt%, and oil displacement tests using natural cores indicates that a tertiary oil recovery of 18.6 ± 0.4% OOIP can be achieved by SP flooding with the N-(3-Oxapropanoxyl)dodecanamide as the main surfactant without adding any alkaline agent and neutral electrolyte. N-(3-Oxapropanoxyl)dodecanamide, as a nonionic surfactant without a cloud point and producible industrially from renewable materials, is an ideal surfactant for SP flooding in the absence of an alkaline agent.     

A Comparative Study on the Aggregation and Thermodynamic Properties of Anionic Sodium Dodecylsulphate and Cationic Cetyltrimethylammonium Bromide in Aqueous Medium: Effect of the Co-solvent N-Methylacetamide

The effect of co‐solvent N‐methylacetamide (NMA) (0.035, 0.046, 0.127, and 0.258 mol kg^?1) on the micellization behaviour of anionic surfactant sodium dodecylsulphate (SDS) (3.21–10.35 mmol kg^?1) and cationic surfactant cetyltrimethylammonium bromide (CTAB) (0.19–3.72 mmol kg^?1) in aqueous solution was explored by employing conductivity measurements at different temperatures (298.15–313.15 K). The critical micelle concentration (CMC) values for SDS and CTAB in aqueous solutions of NMA were determined from the conductivity versus surfactant concentration plots. The variations in the CMC values of SDS with NMA concentration are in striking contrast to those observed in the case of CTAB. The various relevant thermodynamic parameters of micellization, viz. standard enthalpy change, ΔH_m^o, standard entropy change, ΔS_m^o, and standard Gibbs free energy change, ΔG_m^o, were determined using the temperature variation of the CMC values and counterion binding. The results not only relate these thermodynamic parameters to the consequences of intermolecular interactions but are also able to differentiate between SDS–water–NMA and CTAB–water–NMA systems in terms of contributions from head groups as well as alkyl chains of surfactants.