Ultralow Interfacial Tension Research Articles

Progress in research of sulfobetaine surfactants used in tertiary oil recovery

AbstractThe synthesis of sulfobetaine surfactants and their application in tertiary oil recovery (TOR) are summarized in this paper. The synthesis of sulfobetaine surfactants was classified into three categories of single hydrophobic chain sulfobetaine surfactants, double hydrophobic chain sulfobetaine surfactants and Gemini sulfobetaine surfactants for review. Their application in TOR was classified into surfactant flooding, microemulsion flooding, surfactant/polymer (SP) flooding and foam flooding for review. The sulfonated betaine surfactants have good temperature resistance and salt tolerance, low critical micelle concentration (cmc) and surface tension corresponding to critical micelle concentration (γcmc), good foaming properties and wettability, low absorption, ultralow interfacial tension of oil/water, and excellent compatibility with other surfactants and polymers. Sulfobetaine surfactants with ethoxyl structures, hydroxyl and unsaturated bonds, and Gemini sulfobetaine surfactants will become an important direction for tertiary oil recovery because they have better interfacial activity in high‐temperature (≥90°C) and high‐salinity (≥104 mg/L) reservoirs. Some problems existing in the synthesis and practical application were also reviewed.

Imbibition mechanisms of high temperature resistant microemulsion system in ultra-low permeability and tight reservoirs

Lower-phase microemulsions with core-shell structure were prepared by microemulsion dilution method. The high temperature resistant systems were screened and the performance evaluation experiments were conducted to clarify the spontaneous imbibition mechanisms in ultra-low permeability and tight oil reservoirs, and to direct the field microfracture huff and puff test of oil well. The microemulsion system (O-ME) with cationic-nonionic surfactant as hydrophilic shell, No.3 white oil as oil phase core has the highest imbibition recovery; its spontaneous imbibition mechanisms include: the ultra-low interfacial tension and wettability reversal significantly reduce oil adhesion work to improve oil displacement efficiency, the nanoscale “core-shell structure” formed can easily enter micro-nano pores and throats to expand the swept volume, in addition, the remarkable effect of dispersing and solubilizing crude oil can improve the mobility of crude oil. Based on the experimental results, a microfracture huff and puff test of O-ME was carried out in Well YBD43-X506 of Shengli Oilfield. After being treated, the well had a significant increase of daily fluid production to 5 tons from 1.4 tons, and an increase of daily oil production to 2.7 tons from 1.0 ton before treatment.

A Critical Overview of ASP and Future Perspectives of NASP in EOR of Hydrocarbon Reservoirs: Potential Application, Prospects, Challenges and Governing Mechanisms.

Oil production from depleted reservoirs in EOR (Enhanced Oil Recovery) techniques has significantly increased due to its huge demands in industrial energy sectors. Chemical EOR is one of the best approaches to extract the trapped oil. However, there are gaps to be addressed and studied well for quality and cost consideration in EOR techniques. Therefore, this paper addresses for the first time a systematic overview from alkaline surfactant polymer ((ASP)) and future perspectives of nano-alkaline surfactant polymer ((NASP)), its synergy effects on oil recovery improvement, and the main screening criteria for these chemicals. The previous findings have demonstrated that the optimum salinity, choosing the best concentration, using effective nano-surfactant, polymer and alkaline type, is guaranteed an ultra-low IFT (Interfacial Tension). Core flood results proved that the maximum oil is recovered by conjugating nanoparticles with conventional chemical EOR methods (surfactant, alkaline and polymer). This work adds a new insight and suggests new recommendation into the EOR application since, for the first time, it explores the role and effect of nanotechnology in a hybrid with ASP. The study illustrates detailed experimental design of using NASP and presents an optimum micro-model setup for future design of NASP flow distribution in the porous media. The presence of nano along with other chemicals increases the capillary number as well as the stability of chemicals in the solution and strengthens the effective mechanisms on the EOR.

Ultra-low interfacial tension (IFT) zwitterionic surfactant for imbibition enhanced oil recovery (IEOR) in tight reservoirs

Surfactants are effective for imbibition enhanced oil recovery (IEOR) in tight sandstone reservoirs because of their ability to change rock wettability and reduce oil–water interfacial tension (IFT). Different surfactants have different IEOR, and some surfactants even have a negative effect on IEOR. Thus, the selection of an optimum surfactant is necessary for IEOR aiming at different reservoirs. In this study, the static imbibition efficiencies of different surfactants at 50℃ and 2 % KCl were systematically studied by Amott imbibition flask. The imbibition mechanisms and influence factors including salinity and temperature were then investigated by IFT, contact angle (CA), Zeta potential and adhesion energy. The results showed that the zwitterionic surfactant of erucic acid amide propyl betaine (EAPB) could significantly reduce the IFT to ultra-low values (5.7 × 10-4 mN/m) and alter the wettability of sandstone surface at 50℃. The fluidity of oil and capillary force could be effectively improved and the adhesion energy could be reduced, which enabling more pore throats to participate in the imbibition production process. It could be found that the core hydrophilic and IEOR increased with the reduction of IFT. The IEOR of 0.1 % EAPB system reached 44.57 %. The high IEOR and rate can be achieved under the condition of low salinity, high temperature. The IEOR of 0.1 % EAPB was 47.59 % at 2000 mg/L salinity, and 46.61 % at 60℃. This work provides fundamentals for the selection and design of IEOR surfactant in tight oil reservoirs.

Combination of nano-bentonite stabilized foam and ultra-low IFT surfactant additives assisted steam injection to enhanced heavy oil recovery

This study presents an experimental investigation of combination of nano-bentonite stabilized foam and surfactant additives with ultra-low interfacial tension (IFT) to enhance thermal recovery of heavy oil by steam injection. The foam stability results showed that the nano-bentonite can form a three-dimensional network structure to increase the viscosity and thickness of the liquid film, and thus significantly improving the foam stability at high temperature. The foam resistance factor determination demonstrated that the nano-bentonite stabilized foam has good selective plugging ability of reducing the mobility of steam to inhibit the steam channeling. The surfactant additives prepared by the composite system of sodium dodecyl benzene sulfonate and sodium nonylphenol polyoxyethylene ether sulfonate can achieve synergistic effect of high interfacial activity and high-temperature resistance, which can reduce the oil–water interfacial tension to ultra-low level at high temperature. The heterogeneous sandpack flooding results indicated that the nano-bentonite stabilized foam can effectively block the steam channels to improve the sweep efficiency of steam injection and the ultra-low IFT surfactant additives can greatly increase the microscopic oil displacement efficiency. And thus the combination of nano-bentonite stabilized foam and the ultra-low IFT surfactant additives can significantly enhance thermal oil recovery of steam injection in heavy oil reservoirs.

Experimental evaluation of non-ionic mixed surfactant formulations at high-temperature and high-salinity conditions

Non-ionic alkyl polyglucoside (APG) surfactants have been considered as eco-friendly, nontoxic and biodegradable surfactants. This study investigated the feasibility and advantages of new formulations for mixed surfactants consisting of a commerical APG product and one of the following alkyl amines (AAs) – dodecylamine (C12A), tetradecylamine (C14A), hexadecylamine (C16A), and octadecylamine (C18A) for improved oil production applications in carbonate reservoirs under high-temperature and high-salinity (HTHS) conditions. The physicochemical properties including compatibility, surface tension, interfacial tension (IFT), static adsorption, wettability alteration of the solutions comprising APG and various AA under HTHS conditions were evaluated. The self-assemble behavior of molecules between APG and C12A was characterized based on the Scanning Electron Microscopy (SEM) analysis. The formulations with an ultra-low IFT were introduced and the mechanisms resulting in such ultra-low IFT were further studied and discussed. The yielded APG/AA formulation was injected as the chemical flooding agent into a micromodel to investigate the efficiency of oil displacement. Commercial APG products exhibited excellent compatibility with the simulated injection water at reservoir temperature. After mixed with AA, the APG solution became hazy or phase separated above a critical concentration (Ccrit) of AA. Ccrit was found to decrease with an increase of the hydrocarbon chain, suggesting that more APG surfactants are required to solubilize the AA with longer alkyl hydrocarbon chain. In the presence of AA, the critical micelle concentration (CMC) of APG surfactant significantly reduced due to the formation of a compact micellar structure. APG yielded a low IFT at 90 °C and a concentration of 2 g/L in the order of 10−2 mN/m, while an ultra-low IFT in the order of 10−3 mN/m was obtained upon addition of a small amount (0.3–0.5 g/L) of C12A. SEM images and proposed IFT reduction mechanisms indicated that APG and C12A synergistically generated a more compact structure via hydrophobic interaction between the hydrophobic moieties and hydrogen bonding between the hydrophilic parts of the chemicals comparing the aggregated structure formed by APG alone, such effect could eventually lead to a decrease in IFT between oil and water. The amounts of chemical adsorption and contact angle of an oil droplet on carbonate cores were not affected upon addition of AA. The micromodel test showed that the produced oil by injection of the designed APG/AA formulations was further enhanced after water flooding. Among the formulations, APG/C12A flooding resulted in a highest effectiveness on oil displacement with a cumulative oil production of 78.7% at the end of injections. To sum up, new APG/AA-based formulations were designed with an ultra-low IFT resulting from a much compact amphiphilic structure along oil-water interface. This study shows a great potential of APG surfactant and the related formulations in improving oil production for HTHS carbonate reservoirs.

A New Logistically Simple Solution for Implementing Alkali-Surfactant-Polymer/Alkali-Cosolvent-Polymer in Difficult Environments: Evaluation of Concept with High Total Acid Number Viscous Crude Oil

Summary Research on alkali-assisted chemical enhanced oil recovery (EOR) technology [alkali-surfactant-polymer (ASP)/alkali-cosolvent-polymer (ACP)] with high total acid number (TAN) crude oils has led to developments with liquid organic alkalis and cosolvents (Southwick et al. 2020; Fortenberry et al. 2015; Schumi et al. 2019; Upamali et al. 2018). Both concepts afford potential significant cost reduction in field operations, but to date it has not been demonstrated that these two concepts can work together. Monoethanolamine (MEA) alkali and a wide variety of liquid cosolvents are evaluated with high TAN crude oil (1.5 mg KOH/g oil). Formulations are found that give ultralow interfacial tension (UL-IFT) at a specified injection salinity. Fine tuning the formulation to different injection salinities can be done by choosing alternate cosolvents (or a cosolvent blend). A formulation comprising 1% MEA and a novel high molecular weight (3152 g/gmol) cosolvent, 0.5% glycerin alkoxylate with 30 mol of propylene oxide and 35 mol of ethylene oxide (glycerin-30PO-35EO), gave UL-IFT in 21,000 total dissolved solids (TDS) injection brine and gave 100% oil recovery in Bentheimer sandstone with 3,500 ppm FP 3630Ss (SNF Flopaam 3630Sis partially hydrolyzed polyacrylamide) as mobility control agent. All oil was produced clean, no separation of emulsion was needed to measure oil recovery. Alkali consumption tests were also performed with a high-permeability reservoir sandstone. Results confirmed earlier data published with Boise outcrop sandstone (Southwick et al. 2020) showing low alkali consumption with MEA. On a mass basis, only 12% of the amount of MEA is consumed relative to the amount of sodium carbonate consumed. This reduces the logistical challenges of shipping chemicals to remote locations. MEA is also a low-viscosity liquid which further simplifies field handling.

Leveraging ultra-low interfacial tension and liquid-liquid phase separation in embedded 3D bioprinting.

Many recently developed 3D bioprinting strategies operate by extruding aqueous biopolymer solutions directly into a variety of different support materials constituted from swollen, solvated, aqueous, polymer assemblies. In developing these 3D printing methods and materials, great care is often taken to tune the rheological behaviors of both inks and 3D support media. By contrast, much less attention has been given to the physics of the interfaces created when structuring one polymer phase into another in embedded 3D printing applications. For example, it is currently unclear whether a dynamic interfacial tension between miscible phases stabilizes embedded 3D bioprinted structures as they are shaped while in a liquid state. Interest in the physics of interfaces between complex fluids has grown dramatically since the discovery of liquid-liquid phase separation (LLPS) in living cells. We believe that many new insights coming from this burst of investigation into LLPS within biological contexts can be leveraged to develop new materials and methods for improved 3D bioprinting that leverage LLPS in mixtures of biopolymers, biocompatible synthetic polymers, and proteins. Thus, in this review article, we highlight work at the interface between recent LLPS research and embedded 3D bioprinting methods and materials, and we introduce a 3D bioprinting method that leverages LLPS to stabilize printed biopolymer inks embedded in a bioprinting support material.

Percolation Characteristics and Injection Limit of Surfactant Huff-n-Puff in a Tight Reservoir.

For the development of tight reservoirs, large-scale volume fracturing is frequently utilized as an effective production enhancement strategy. However, there is a significant decrease in productivity after fracturing. Improvement of production through secondary surfactant huff-n-puff has become one of the methods. In this paper, the characteristics of surfactant percolation during huff-n-puff were analyzed from macroscopic and microscopic perspectives. The production variation characteristics of the huff-n-puff were calculated by experiments and numerical methods. From Stokes' equations and phase field equations, solutions were found to analyze the effect of interfacial properties on surfactant percolation from the microscopic perspective. The findings demonstrated that a surfactant with a high displacement efficiency could not considerably increase huff-n-puff production, whereas the percolation rate had a wider influence. The surfactant with ultralow interfacial tension (<1 × 10-2 mN/m) and a higher wetting angle (>12.6°) has a faster percolation rate. Significant huff-n-puff production can be obtained in the percolation rate range of 1.38 to 1.63 m/PV. Simultaneously, the concepts of limit and optimal injection volume were established and utilized to characterize the influence of injection parameters on production under nonextension fracture situations. Based on the data, in order to obtain high production in a short time, the injection strength should be near to the value at fracture extension, and the optimum injection volume is 1000-1200 m3/m. The findings of this study have the potential to guide the selection of the surfactant and injection parameters in the field.

Renewable non-edible oils derived long chain (C24.1) bio-based zwitterionic surfactant with ultralow interfacial tension between crude oil and formation brine

A new ultra-long chain monounsaturated 4-(N-nervonicamidopropyl-N,N-dimethylammonium) butane sulfonate (NDAS) zwitterionic surfactant with ultralow interfacial tensions was developed through the modification of nervonic acid derived from renewable non-edible seed oils by a simple and effective method. Its structure was characterized by ESI-HRMS, 1H NMR, and 13C NMR. NDAS surfactant exhibited a strong interfacial activity (∼10−4 mN/m) between the crude oil and the formation brine at a very low surfactant dosage (0.05 g/L) and at high salinity conditions, which is equivalent to 2% (w/w) of dosage of the most traditional surfactants used in the enhanced oil recovery field. Meanwhile, at a very low concentration (0.05 g/L), NDAS demonstrated strong NaCl compatibility up to 100 g/L, Ca2+ ions compatibility up to 200 mg/L, and temperature stability up to 90 °C. The surface tension, emulsification, and biodegradability parameters were also evaluated. This work consolidates our hypothesis that increasing the hydrophobic chain length of a surfactant certainly contributes to the high interfacial activity and good compatibility of salts and temperatures. Hence, it will facilitate the design of a sustainable alternative to petroleum-based chemicals to develop bio-based surfactants and extend the domain of bio-based surfactants to new applications such as in enhanced oil recovery (EOR).

The mechanism for lowering interfacial tension by extended surfactant containing ethylene oxide and propylene oxide groups

In this work, the interfacial tensions (IFTs) of a series of alkyl ether carboxylates containing different ethylene oxide (EO) and propylene oxide (PO) groups (C12PO15EO5C, C12PO15EO10C and C12PO15EO15C) against n-alkanes were investigated. Based on the experimental and theoretic results, we find that for adsorbed extended surfactant molecules with both PO and EO groups, the PO group stretches towards the oil phase in a helical winding manner, which improves the size of hydrophobic part and decreases IFT. On the other hand, the whole EO group arranges in an “L” pattern with 4 EO flat at the interface and the others stretching into the water. The “dumbbell” type with the large size of the ionic head and PO group at both ends and the linear EO chain in the middle results in the high IFT values. Therefore, a sufficient PO number and few EO number are prerequisites for obtaining ultralow IFT. The addition of NaCl can decrease the size of anionic head and C12PO15EO5C solution can produce ultralow IFT against hydrocarbons at optimized salinity. However, electrolyte shows little effect on the IFTs of extended surfactants with “dumbbell” conformation at the interface because the size of linear EO group plays the crucial role. Our research has important implications for the in-depth understanding of extended surfactants and their application in high-salt reservoirs.

Synergetic System of Zwitterionic/Anionic Surfactants with Ultralow Interfacial Tension and High Salt Resistance for Enhancing Heavy Oil Recovery

Synergetic System of Zwitterionic/Anionic Surfactants with Ultralow Interfacial Tension and High Salt Resistance for Enhancing Heavy Oil Recovery

Elucidation of the mechanistic aspects of chemical EOR in viscous oil systems

Chemical enhanced oil recovery techniques have been suggested as efficient alternatives to thermal methods in many thin/small viscous oil reservoirs in western Canada. These acidic oil reservoirs have been screened as good candidates for alkaline (A) and surfactant (S) floods. In this study, sand-pack core flooding experiments and pore-scale microfluidic tests were designed to give some new insights on the mechanisms of AS floods augmented with polymer (P) solutions in viscous oil systems.Viscous oil samples from Luseland field (14,850 mPa s at 25 °C) was used in all the experiments. The most efficient chemical generates ultralow interfacial tension, 0.002 mN/m, producing low viscosity type II (+) emulsion (740 mPa s, which is much lower than the viscosity of originating oil). The two pore volumes injection of this cocktail results in around 20% OOIP incremental oil recovery, which is almost doubled after injecting two pore volumes of extended water. The core effluents were all low viscosity oil in water emulsions, consistent with observations in batch mixing experiments. The incremental oil recovery to ASP flood is almost twice the recovery obtained in the polymer flood with nearly 4.5 times larger pressure build-up across the core. These observations suggest that the main mechanism is emulsification and oil entrainment rather than improvement in sweep efficiency.These speculated mechanisms based on the core scale observations were verified through the results of the microfluidic experiments. ASP solution can efficiently penetrate the residual ganglia or the edge of the water channels from which oil can be efficiently stripped. This oil is easily entrained in the form of low viscosity oil in water emulsions. Our results emphasize the critical role of polymer in the cocktail. In the absence of polymer, AS cannot efficiently penetrate the residual viscous oil leading to only a minuscule improvement in oil recovery.

Experimental study on the imbibition mechanism of the Winsor type Ⅰ surfactant system with ultra-low IFT in oil-wet shale oil reservoirs by NMR

Surfactants enhanced spontaneous imbibition is an effective method to improve the oil recovery of shale reservoirs. The popular perspective believes that the wettability alteration and the capillary force are the primary mechanisms. Thus a water-wet condition and a relatively high interfacial tension (IFT) are required. However, in this work, we found that the Winsor type I surfactant solution with ultra-low IFT performed better than other relatively higher-IFT solutions with the capillary effect in oil-wet shale reservoirs. The contact angle, spontaneous imbibition recovery and phase behavior of the Winsor type I surfactant solutions were measured and compared with the solutions with relatively high IFT, including water, nonionic, and anionic surfactant solutions. The results demonstrated that anionic surfactants and Winsor type I surfactant solutions could alter the wettability to a water-wet condition, while the nonionic surfactants could only change to an intermediate-wet state. Both the anionic surfactants and Winsor type I surfactant solutions could displace the oil from micropores and mesopores. Still, the Winsor type I surfactant solutions with ultra-low IFT showed a better performance than the anionic surfactants with relatively high IFT. The interfacial micrographs of the Winsor type I surfactant solutions in contact with the oil phase manifested that the Winsor type I surfactant solutions changed the recovery patterns from two-phase flow driven by capillary force to the migration of microemulsions and emulsions driven by diffusion and gravity. The over-equilibrium Winsor type Ⅲ microemulsions and emulsions are rapidly formed near the oil-water interface. After that, the over-equilibrium Winsor type Ⅲ microemulsions are gradually diluted to Winsor type Ⅰ microemulsions and dissolved in a fresh surfactant solution. At the same time, the emulsions diffuse firstly, then coalesce and migrate out of the pore mediums driven by buoyancy. The water-wet condition and capillary force are not significant for this flow pattern, thus the Winsor type I surfactant solutions with ultra-low IFT are especially effective in recovering the oil of oil-wet micropores and mesopores. This work provides a new way of exploiting the oil in organic matter pores that can barely change to water-wet conditions.

Study Reviews Recent Polymerflooding Advances in China

This article, written by JPT Technology Editor Chris Carpenter, contains highlights of paper SPE 200084, “Recent Advances of Polymerflooding in China,” by Hu Guo and Kaoping Song, China University of Petroleum, and Yuming Wang, Daqing Oilfield Company, et al. The paper has not been peer reviewed. Polymerflooding is one of the more promising chemical enhanced oil recovery (EOR) techniques that features high incremental oil recovery factor, low cost, and wide reservoir applicability. This paper helps clarify ideas regarding polymerflooding implementation based on theory and practice in China. Introduction Laboratory studies aimed at increasing understanding of polymerflooding involve criteria for matching polymer with porous media, the polymer viscoelasticity effect on residual oil saturation (ROS), and displacement efficiency and synthesis of new polymers with better viscosifying capacity compared with typical partially hydrolyzed polyacrylamide (HPAM). The plugging of injectors in many oil fields is becoming increasingly common in many commercial blocks. This problem is especially serious for high-concentration polymer-injection blocks in fields such as Daqing, Xinjiang, and Henan. Understanding this phenomenon involves aligning the polymer and porous-media parameters such as permeability and pore size. Actual reservoir pressure distribution also must be considered. Because modern chemical EOR is based on ultralow interfacial tension (IFT) and minimum mobility ratio theory, the idea of combining the benefits of reducing IFT and increasing displacing-phase viscosity leads to a synthesis of amphiphilic polymers, which have features of both polymers and surfactants. This new type of polymer is sometimes called polymeric surfactant in China.

Developing a novel procedure in utilizing pendant drop method for determination of ultra-low interfacial tension and surface tension in near-miscibility conditions

One of the procedures to measure the surface and interfacial tension (ST and IFT) is pendant drop tensiometry which has distinguished drawbacks to determine the ultra-low interfacial tension. The main drawbacks of previous pendant drop procedures were incapacitation for the drop formation at ultra-low IFT values, inability to provide a suitable photo for small needles, and drop formation with non-uniform discharges. Refer to the lack of a comprehensive method for measuring all ranges of IFT and ST from ultra-low to high values felt by considering the porous media limitation in many unique studies, such as enhanced oil recovery (EOR), and carbon capture and storage (CCS), to cover the fluid-fluid and gas-fluid interactions, improving the pendant drop method is to be crucial. In this study, a new procedure was introduced to measure the ultra-low IFT in order of 10−3 mN m−1 using different needles with an outer diameter (OD) of 31G (0.46 mm) to 34G. The needles were used in this study had OD from 34G (0.16 mm) to 14G (2.11 mm) to provide a wide range of IFT and ST values from ultra-low to high values. At last, a comprehensive table was made based on more than 450 IFT and ST results to assist the researchers in selecting the best type of needle for performing the pendant drop test according to the range of IFT and ST values by considering varied applications.

Ferrofluidic aqueous two-phase system with ultralow interfacial tension and micro-pattern formation

Ferrofluids are magnetic liquids known for the patterns they form in external magnetic fields. Typically, the patterns form at the interface between a ferrofluid and another immiscible non-magnetic fluid with a large interfacial tension γ ∼ 10−2 N m−1, leading to large pattern periodicities. Here we show that it is possible to reduce the interfacial tension several orders of magnitude down to ca. γ ∼ 10−6 N m−1 by using two immiscible aqueous phases based on spontaneous phase separation of dextran and polyethylene glycol and the asymmetric partitioning of superparamagnetic maghemite nanoparticles into the dextran-rich phase. The system exhibits classic Rosensweig instability in a uniform magnetic field with a periodicity of ∼200 μm, significantly lower than in traditional systems (∼10 mm). This system paves the way towards the science of pattern formation at the limit of vanishing interfacial tension and ferrofluid applications driven by small external magnetic fields.

Progress in all-aqueous droplets generation with microfluidics: Mechanisms of formation and stability improvements.

All-aqueous systems have attracted intensive attention as a promising platform for applications in cell separation, protein partitioning, and DNA extraction, due to their selective separation capability, rapid mass transfer, and good biocompatibility. Reliable generation of all-aqueous droplets with accurate control over their size and size distribution is vital to meet the increasingly growing demands in emulsion-based applications. However, the ultra-low interfacial tension and large effective interfacial thickness of the water-water interface pose challenges for the generation and stabilization of uniform all-aqueous droplets, respectively. Microfluidics technology has emerged as a versatile platform for the precision generation of all-aqueous droplets with improved stability. This review aims to systematize the controllable generation of all-aqueous droplets and summarize various strategies to improve their stability with microfluidics. We first provide a comprehensive review on the recent progress of all-aqueous droplets generation with microfluidics by detailing the properties of all-aqueous systems, mechanisms of droplet formation, active and passive methods for droplet generation, and the property of droplets. We then review the various strategies used to improve the stability of all-aqueous droplets and discuss the fabrication of biomaterials using all-aqueous droplets as liquid templates. We envision that this review will benefit the future development of all-aqueous droplet generation and its applications in developing biomaterials, which will be useful for researchers working in the field of all-aqueous systems and those who are new and interested in the field.

Experimental investigation on remaining oil distribution and recovery performances after different flooding methods

Nowadays most of the oilfield in China have entered the middle-late development stages with the problem of high water cut and low permeability. Many studies have been conducted on the mechanism of chemical flooding to enhance oil recovery. However, there has been less previous evidence for accurate identification and distribution of remaining oil. Therefore, we proposed a new nuclear magnetic resonance (NMR) interpretation method as well as a new residual oil fluorescence analysis method. In this study, we conducted core displacement experiments with different methods. The nuclear magnetic resonance (NMR) tests and fluorescence analysis of frozen slides were performed in each stage after flooding to study the effect of different displacement methods on the recovery degree and the remaining oil distribution. The results showed that alkali can only slightly improve the recovery of macropores and free-state oil due to its poor sweep volume and oil washing efficiency. Surfactants can increase oil recovery in mesopores and the type of bound-state remaining oil by reducing interfacial tension (IFT). Although the injection of polymer can enlarge the sweep volume, the effect of displacement efficiency is poor in narrow space. Therefore, it can only improve the recovery factor in smallpores and mesopores as well as the type of free-state remaining oil. The synergistic effect of ASP system not only can form ultra-low interfacial tension to enhance the recovery of bound-state and half-bound state, but also can help surfactants and alkali enter smallpores according to the injection of polymer. Thus, the oil recovery is significantly improved. Moreover, our study provided a micro-level understanding as the occurrence state and distribution of remaining oil. The result also lays the foundation for further enhance oil recovery in oilfield.

In situ micro-emulsification during surfactant enhanced oil recovery: A microfluidic study

HypothesisIt is generally believed that the improved efficiency of surfactant enhanced oil recovery (EOR) comes from ultra-low interfacial tension (IFT) between oil and surfactant solution owing to the formation of middle-phase microemulsion. However, hindered visibility in underground porous media prevents direct observation of in situ generation of middle-phase microemulsion during surfactant flooding. Thus, direct visualization of the process is vital, and could clarify its contribution to EOR. ExperimentsMicro-emulsification of a displacing fluid containing sodium 4-dodecylbenzenesulfonate and alcohol propoxy sulfate with model oil was investigated. Phase diagrams were drawn using salinity scans, and the influence of polymer on emulsification was analyzed. Micro-emulsification was monitored through in situ fluorescent tagging via 2D-microfluidics and ex situ visualization via cryo-electron microscopy and small angle X-ray scattering. Its contribution to the oil recovery factor was quantified by measuring the volume of each phase in the eluates. FindingsOn-chip experiments indicated that in situ micro-emulsification occurred when the prescreened surfactant solution flowed in contact with trapped oil. The aqueous phase initially invaded the residual oil, forming a low mobility microemulsion. This microemulsion was then diluted by subsequent displacing fluid, forming a new driving fluid that caused ultra-low IFT in the trapped oil downstream. Under the synergistic effect of micellar solubilization and trapped-oil mobilization, the recovery factor could be increased by up to 40% over waterflooding and 43% on polymer inclusion in the formulation.