Salt-Induced Constructions of Gemini-like Surfactants at the Interface and Their Effects on the Interfacial Tension of a Water/Model Oil System

It is an urgent issue to enhance oil recovery for unconventional reservoirs with high salinity. Focused on this topic, salt addition is a powerful tool to motivate the surfactant assembly at the water/oil interface and improve the interfacial activity. We used a cationic surfactant cetyltrimethylammonium bromide (CTAB) and an anionic salt dicarboxylic acid sodium (CnDNa) to construct gemini-like surfactants at the interface and evaluated their ability to reduce the interfacial tension (IFT) between model oil (toluene and n-decane, v:v = 1:1) and water. Interestingly, the fabrication of a (CTAB)₂/C4DNa gemini-like surfactant was hardly achieved at the fresh water/model oil interface, but accomplished at the brine/model oil interface. At a high NaCl concentration (100,000 mg L⁻¹), the IFT value is reduced to 10⁻³ mN m⁻¹ order of magnitude, which is generally desired in practical applications. The control experiments displacing the surfactant type and the spacer length further confirmed the NaCl effects on the interfacial assembly.     

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.     

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.     

Optimization of Dynamic Interfacial Tension for Crude Oil–Brine System in the Presence of Nonionic Surfactants

In this study, interfacial tension (IFT) is measured between brine and crude oil (a sample of heavy oil from an Iranian oil reservoir) in the presence of two nonionic surfactants, KEPS 80 (Tween 80) and Behamid D, at different concentrations in order to optimize the concentrations of the surfactants. The surface response method is used to design the IFT measurement experiments. The experimental design and optimization is performed using the IFT as an objective function and temperature, concentration, and time as independent variables. In addition to the IFT measurement, various experiments such as stability tests of the surfactants in NaCl brine solutions, adsorption experiments on the carbonated rock surface, and phase behavior tests are performed to investigate the behavior of KEPS 80 and Behamid D in the enhanced oil recovery process. At the end, a model using the response surface statistical technique is designed for optimization of the concentrations of the surfactants, and a surfactant molecular migration mechanism is used for explanation of the dynamic IFT variation versus time. In the case of IFT experiments, the effect of surfactant concentration (at 1000, 3000, and 5000 ppm) on the dynamic IFT is investigated. The experiments are performed at four temperatures (25, 40, 50, and 67°C). The results show that the oil–brine IFT values can be reduced to about 4 mN m⁻¹ in the presence of Behamid D and to about 1 mN m⁻¹ in the presence of KEPS 80 at low concentrations.     

Surfactant Enhanced Oil Recovery in a High Temperature and High Salinity Carbonate Reservoir

The goal of this work was to find an effective surfactant system for enhanced oil recovery after water injection substituting for oil at a vuggy fractured reservoir with a high temperature and high salinity (220,000 mg/L). Four types of surfactants with concentrations (less than 0.2 %) were screened. Washing oil experiments were conducted in Amott cells. A surfactant system was established by mixing a surfactant with best ultimate recovery and one with best recovery rate. The optimized surfactant system could recover 50 % of remaining oil. To study the mechanism of enhanced oil recovery after water injection substituting oil, interfacial tension (IFT) and contact angle were measured. Experimental results showed that surfactants with good washing ability had low IFT, but surfactants with low IFT may not have a good washing ability. IFT had no obvious relationship with the increased oil recovery or washing ability. The optimized system could not alter carbonate to decrease the oil‐wetting capability. Though octadecyl trimethyl ammonium chloride had a good ability wet the carbonate with water, it could not recover much oil. Therefore, except for interfacial tension and wettability alteration, there must be other parameters dominating oil recovery after water injection substituting for oil.     

Synergistic Effects between Anionic and Sulfobetaine Surfactants for Stabilization of Foams Tolerant to Crude Oil in Foam Flooding

In foam flooding, foams stabilized by conventional surfactants are usually unstable in contacting with crude oil, which behaves as a strong defoaming agent. In this article, synergistic effects between different surfactants were utilized to improve foam stability against crude oil. Targeted to reservoir conditions of Daqing crude oil field, China (45 °C, salinity of 6778 mg L⁻¹, pH = 8–9), foams stabilized by typical anionic surfactants fatty alcohol polyoxyethylene ether sulfate (AES) and sodium dodecyl sulfate (SDS) show low composite foam index (200–500 L s) and low oil tolerance index (0.1–0.2). However, the foam stability can be significantly improved by mixing the anionic surfactant with a sulfobetaine surfactant, which behaves as a foam stabilizer increasing the half-life of foams, and those with longer alkyl chain behave better. As an example, by mixing AES and SDS with hexadecyl dimethyl hydroxypropyl sulfobetaine (C₁₆HSB) at a molar fraction of 0.2 (referring to total surfactant, not including water), the maximum composite foaming index and oil tolerance index can be increased to 3000/5000 L s and 1.0/4.0, respectively, at a total concentration between 3 and 5 mM. The attractive interaction between the different surfactants in a mixed monolayer as reflected by the negative β^s parameter is responsible for the enhancement of the foam stabilization, which resulted in lower interfacial tensions and therefore negative enter (E), spreading (S), and bridging (B) coefficients of the oil. The oil is then emulsified as tiny droplets dispersed in lamellae, giving very stable pseudoemulsion films inhibiting rupture of the bubble films. This made it possible to utilize typical conventional anionic surfactants as foaming agents in foam flooding.     

Viscoelastic Surfactants with High Salt Tolerance,Fast‐Dissolving Property,and Ultralow Interfacial Tension for Chemical Flooding in Offshore Oilfields

Injected chemical flooding systems with high salinity tolerance and fast‐dissolving performance are specially required for enhancing oil recovery in offshore oilfields. In this work, a new type of viscoelastic‐surfactant (VES) solution, which meets these criteria, was prepared by simply mixing the zwitterionic surfactant N‐hexadecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propane sulfonate (HDPS) or N‐octyldecyl‐N,N‐dimethyl‐3‐ammonio‐1‐propane sulfonate (ODPS) with anionic surfactants such as sodium dodecyl sulfate (SDS). Various properties of the surfactant system, including viscoelasticity, dissolution properties, reduction of oil/water interfacial tension (IFT), and oil‐displacement efficiency of the mixed surfactant system, have been studied systematically. A rheology study proves that at high salinity, 0.73 wt.% HDPS/SDS‐ and 0.39 wt.% ODPS/SDS‐mixed surfactant systems formed worm‐like micelles with viscosity reaching 42.3 and 23.8 mPa s at a shear rate of 6 s^?1, respectively. Additionally, the HDPS/SDS and ODPS/SDS surfactant mixtures also exhibit a fast‐dissolving property (dissolution time <25 min) in brine. More importantly, those surfactant mixtures can significantly reduce the IFT of oil–water interfaces. As an example, the minimum of dynamic‐IFT (IFT_min) could reach 1.17 × 10^?2 mN m^?1 between the Bohai Oilfield crude oil and 0.39 wt.% ODPS/SDS solution. Another interesting finding is that polyelectrolytes such as sodium of polyepoxysuccinic acid can be used as a regulator for adjusting IFT_min to an ultralow level (<10^?2 mN m^?1). Taking advantage of the mobility control and reducing the oil/water IFT of those surfactant mixtures, the VES flooding demonstrates excellent oil‐displacement efficiency, which is close to that of polymer/surfactant flooding or polymer/surfactant/alkali flooding. Our work provides a new type of VES flooding system with excellent performances for chemical flooding in offshore oilfields.     

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.     

Effect of sodium dodecyl benzene sulfonate on the absorption spectrum and determination of crystal violet in aqueous solution

The effect of sodium dodecyl benzene sulfonate (SDBS) on the absorption spectrum of crystal violet (CV) in an aqueous solution was studied by spectrophotometry. The results showed that when the SDBS concentration was lower than the critical micelle concentration (CMC), the absorption spectrum of CV was altered significantly. However, the effect was eliminated when the SDBS concentration was higher than the CMC, and the absorption maximum of the solution gradually reached that of a SDBS-free CV solution. A new method was thus proposed for the determination of the CV concentration in an aqueous solution containing an anionic surfactant. Under the optimal conditions, i.e., a detection wavelength of 584 nm, a SDBS concentration of 4.8 mmol L⁻¹ and a reaction time of 1 h, the linear range of the method was 0.16 × 10⁻² mmol L⁻¹–1.6 mmol L⁻¹.     

Superior enhancement of imbibition recovery by novel surfactant mixtures with a large hydrophobic group combined with nanosilica

Low interfacial tension (IFT) drainage and imbibition are effective methods for improving oil recovery from reservoirs that have low levels of oil or are tight (i.e., exhibit low oil permeability). It is critical to prepare a high efficient imbibition formula. In this work, a novel 2,4,6-tris(1-phenylethyl)phenoxy polyoxyethylene ether hydroxypropyl sodium sulfonate (TPHS) surfactant was synthesized and evaluated for imbibition. Its structure was confirmed by Fourier transform infrared spectroscopy and the interfacial tension (IFT) of the crude oil/0.07% TPHS solution was 0.276 mN/m. When 0.1 wt% TPHS was mixed with 0.2 wt% alpha olefin sulfonate (AOS), the IFT was lowered to 6 × 10⁻² mN/m. The synergy between nanoparticles (NPs) and TPHS/AOS mixed surfactant was studied by IFT, contact angle on sandstone substrates, zeta potential, and spreading dynamics through microscopic methods. The results show that the surfactant likely adsorbs to the NP surface and that NP addition can help the surfactant desorb crude oil from the glass surface. With the addition of 0.05 wt% SiO₂ NPs (SNPs), the imbibition oil recovery rate increased dramatically from 0.32%/h to 0.87%/h. The spontaneous imbibition recovery increased by 4.47% for original oil in place (OOIP). Compared to flooding by TPHS/AOS surfactant solutions, the oil recovery of forced imbibition in the sand-pack increased by 12.7% OOIP, and the water breakthrough time was delayed by 0.13 pore volumes (PV) when 0.05% SNPs were added. This paper paves the way for enhanced oil recovery in low-permeability sandstone reservoirs using novel TPHS/AOS surfactants and SNPs.     

Preparation and Characterization of an Anionic Gemini Surfactant for Enhanced Oil Recovery in a Hypersaline Reservoir

A new type of anionic Gemini surfactant (AGS) was designed and prepared by a simple, low–cost, and green method, and its properties were characterized. The results showed that the values of parameters such as critical micelle concentration (CMC) value, Γmax, Amin, and pC20 of AGS were 0.10 mmol L⁻¹, 1.62 mmol m⁻², 1.02 nm², and 4.60, respectively, indicating that AGS is highly surface active. AGS has a very good synergistic effect with lauryl diethanol amide (6501), and the mixture surfactant 6501DA (composed of AGS and 6501 with a mass ratio of 1:2.5) has good wetting and emulsifying ability of the crude oil and good resistance to calcium and magnesium ions. In the temperature range from 50 to 70 °C, salinity of 20,000–50,000 mg L⁻¹ of the simulated formation water, and dosage of 6501DA from 500 to 3000 mg L⁻¹, all the interfacial tension (IFT) values between the 6501DA solution and Bamianhe crude oil were lower than 10⁻² mN m⁻¹, and all the adsorption amounts of oil sand to 6501DA in solution were less than 2 mg g⁻¹, indicating that AGS has potential for application in EOR in a hypersaline reservoir.     

The effect of mixed surfactants on enhancing oil recovery

Micelles composed of mixed surfactants with different structures (mixed micelles) are of great theoretical and industrial interest. This work pertains tomaximizing interfacial tension (IFT) reduction via surfactant pairs. In this respect, four types of fatty acid amides based on lauric, myristic, palmitic, and stearic acids were blended with dodecyl benzene sulfonic acid at a molar ratio of 4∶1 and designated as A₁, A₂, A₃, and A₄, respectively. The IFT was measured for each blend at different concentrations using Badri crude oil. The most potent formula (A₄) was evaluated for using in enhanced oil recovery (EOR). The IFT was tested in the presence of different electrolyte concentrations with different crude oils at different temperatures. Finally several runs were devoted to study the displacement of Badri crude oil by A₄ surfactant solution using different slug sizes of 10, 20, and 40% of pore volume (PV). The study reveled that Badri crude oil gave ultra-low IFT at lowest surfactant concentration and 0.5% of NaCl. The recovery factor at a slug size of 20% PV was 83% of original oil in place compared with 59% in case of conventional water flood.     

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%.     

Novel alkyl methylnaphthalene sulfonate surfactants: A good candidate for enhanced oil recovery

The surface tensions of various surfactant aqueous solution and the dynamic interfacial tensions between the Shengli oil field of China crude oil and the solution of novel surfactants, a series of single-component alkylmethylnaphthalene sulfonates (AMNS) including various the length of alkyl chains (hexyl, octyl, decyl, dodecyl and tetradecyl, developed in our laboratory), were measured. It is found that synthesized surfactants exhibited great capability and efficiency of lowering the solution surface tension. The critical micelle concentrations, CMC were: 6.1–0.018×10⁻³ mol L⁻¹, and the surface tensions at CMC, γ_CMC were: 28.27–35.06 mN m⁻¹. It is also found that the added surfactants are greatly effective in reducing the interfacial tensions and can reduce the tensions of oil–water interface to ultra-low, even 10⁻⁶ mN m⁻¹ at very low surfactant concentration without alkali. The addition of salt, sodium chloride, results in more effectiveness of surfactant in reducing interfacial tension and shows that there exist obviously both synergism and antagonism between the surfactant and inorganic salt. All of the synthesized surfactants, except for hexyl methylnaphthalene sulfonate, can reduce the interfacial tension to ultra-low at an optimum surfactant concentration and salinity. Especially Tetradec-MNS surfactant is most efficient on lowering interfacial tension between oil and water without alkaline and the other additives at a 0.002 mass% of very low surfactant concentration. Both chromatogram separation of flooding and breakage of stratum are avoided effectively, in addition to the less expensive cost for enhanced oil recovery, and therefore it is a good candidate for enhanced oil recovery.     

Ultralow oil-water IFTs using neutralized oxidized hydrocarbons as surfactants

Surfactants that may be suitable for application in enhanced oil recovery have been produced from C₂₂ and C₂₆ paraffinic and naphthenic petroleum fractions by a two-step process. The hydrocarbon feed stocks were first oxidized in the vapor-phase, followed by neutralization of the oxidized products with aqueous alkali. As a result, dilute solutions of organic acid salts were produced that achieved ultralow (<10⁻² dyne/cm) interfacial tensions against a synthetic oil. Surfactant solutions that exhibited the lowest interfacial tensions (IFTs) were prepared from neutralizations that used low concentrations of sodium hydroxide rather than sodium silicate, sodium tripolyphosphate, or sodium carbonate. Neutralizations that used sodium silicate or sodium carbonate resulted in surfactant solutions having IFT profiles that were less sensitive to the electrolyte concentration. When sodium hydroxide was combined with either sodium silicate or sodium tripolyphosphate in the neutralizations, solutions having intermediate IFT properties were produced. The amount of alkali used in the neutralizations was observed to affect the IFT properties of the resultant surfactant solution. The electrolyte concentration at which the minimum IFT occurred was inversely related to the pH of the surfactant solution. For surfactant solutions of common pH prepared from different concentrations of oxidized product, the minimum IFTs all occurred at the same concentration of electrolyte. Surfactant solutions remained interfacially active even in the presence of significant concentrations of calcium chloride. One pore volume of a solution containing only about 1% of active surfactant recovered 42.0% of the residual oil in a tertiary core-flood experiment.     

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.     

Novel surfactants for ultralow interfacial tension in a wide range of surfactant concentration and temperature

This work investigates the possibility of injecting dilute aqueous solutions of novel surfactants into the Yibal field (Sultanate of Oman). This was accomplished through an experimental protocol based on the following criteria: (i) compatibility of the surfactants with the high-saline reservoir water (∼200 g/L); (ii) low interfacial tension (IFT) between crude oil and reservoir water (less than 10⁻² mN m⁻¹); and (iii) maintaining the low IFT behaviour during the entire surfactant flooding. Novel surfactants selected in this study consist of a series of ether sulfonates (AES-205, AES-128, AES-506, and 7–58) and an amphoteric surfactant (6–105). These surfactants were found to be compatible with reservoir water up to 0.1% surfactant concentration, whereas 6–105 and 7–58 showed compatibility within the full range of surfactant concentration investigated (0.001–0.5%). All surfactant systems displayed dynamic IFT behavior, in which ultralow transient minima were observed in the range 10⁻⁴–10⁻³ mN m⁻¹, followed by an increase in the IFT to equilibrium values in the range 10⁻³–10⁻¹ mN m⁻¹. The results also showed that with respect to concentration (0.05–0.5%) and temperature (45–80°C), AES-205 and 7–58 surfactants exhibit a wide range of applicability, with the IFT remaining below 10⁻² mN m⁻¹, as required for substantial residual oil recovery. In addition, ultralow IFT were obtained at surfactant concentrations as low as 0.001%, making the use of these surfactants in enhanced oil recovery extremely cost-effective.     

Study of a Novel Carboxylic Cellulose Nanofibrils-Ethoxylated Phytosterol-Alcohol Environmentally Friendly System on the Application in Enhanced Oil Recovery

Bio-polymers and bio-surfactants have attracted increasing attention for their application in chemical enhanced oil recovery (EOR) due to the environmental concerns of synthetic chemical agents. Here, a ternary compound system consisted of carboxylic cellulose nanofibrils (CCNF), ethoxylated phytosterol (BPS), and n-pentanol was constructed. The rheological property and interfacial activity of the compound system and the effects of each component at high temperature (80 °C) was investigated systematically. The ternary compound system exhibited excellent performance in thickening, IFT reduction (<10⁻² mN m⁻¹), emulsification, and better salt tolerance. CBP, the ternary system of CCNF (2000 mg L⁻¹), BPS (2000 mg L⁻¹), and n-pentanol (5000 mg L⁻¹), greatly enhanced the oil recovery (24.3%) in the core flooding tests by its high displacement efficiency and sweep enlargement, which was demonstrated directly in the visual micromodel flooding. As an eco-friendly system with remarkable performance, the compound system of CBP shows great application potential in EOR.     

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.     

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.