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The salinity seriously affects the recovery efficiency of surfactant flooding, and it is demonstrated the introduced ethoxy (EO) groups can enhance the interfacial activity of surfactants at harsh salinity via various experimental methods. In this study, sodium dodecyl sulfate (SDS) and sodium dodecyl ether sulfate (AES) are selected to investigate the effects of EO group number on the salt resistance of surfactants at the air/water interface by experiments and molecular dynamics (MD) simulation method. Optical microscopy and static multiple light scattering results show that the AES stabilized emulsions with Ca2+ ions have better stability than those of SDS, which is further explored by molecular MD simulation method. The interface formation energy (IFE) and self-diffusion coefficients (D α) are calculated to systematically study the effects of introduced EO group number on calcium resistance of surfactants. The interaction between surfactants and Ca2+ ions at the oil/water interface is evaluated by the potential of mean of force (PMF) and the radial direction functions (RDF), which is confirmed by the calculation of molecular electrostatic potential (MEP) and coordination number. The simulation results indicate that the introduced EO groups can combine Ca2+ ions to fabricate salt bridge via intermolecular or intramolecular interactions to highly improve the calcium resistance of surfactants. The present work proposes a microcosmic perspective of the roles of EO group number on the calcium resistance of AES at the oil/water interface. [Display omitted] • The effects of EO groups on calcium resistance were illustrated by MD simulation. • EO groups improved interfacial activity of surfactants in presence of Ca2+ ions. • The introduced EO groups changed the MEP and coordination number of surfactants. • The O atoms in the EO groups could form salt bridge with Ca2+ ions. [ABSTRACT FROM AUTHOR]

A mixed cationic surface-active ionic liquid/anionic surfactant system consisting of N -dodecyl- N -methylpyrrolidinium bromide (L12) and sodium dodecyl sulfate (SDS) was used for chemical enhanced oil recovery (EOR). The mixed L12/SDS surfactant system could cause remarkable effects on the interfacial tension (IFT) between water and a model oil (toluene and n -decane, v:v = 1:1), and the strength of the effect depended on the L12/SDS molar ratio. The effects of temperature and salinity on the IFT were systematically investigated to verify the mechanism of the mixed surfactants at the interface. Moreover, the mixed L12/SDS surfactant system showed the desired ability to reduce the IFT of water/crude oil, greatly improving oil recovery with the assistance of a polymer in core flooding tests. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) are incredibly efficient additives to solve wellbore instability resulting from shale hydration. The influence of the molecular structure of ILs on their inhibition performance has been investigated intensively, and hydroxyl is regarded as the significant group to improve their inhibition performances. In this study, three novel dihydroxyl ionic liquids (DHILs) including [C 4 DIPA]Br, [C 8 DIPA]Br, and [C 12 DIPA]Br were successfully synthesized. Then their thixotropy and inhibition properties were evaluated via three-interval thixotropy tests (3ITTs), hot-rolling recovery tests, immersion tests, and linear swelling tests. [C 12 DIPA]Br exhibited the optimal inhibition ability at a low concentration (0.5 wt%) and was more effective than the conventional inhibitor KCl (2 wt%). Various techniques were used to analyze the inhibition mechanism of DHILs including contact angle measurements, zeta potential, X-ray diffraction, and Flourier transform infrared spectroscopy. The results demonstrated that the synergistic effects of hydrogen bonding, electrostatic interaction, and hydrophobic shield should be responsible for the excellent inhibition performance and great thermal stability of [C 12 DIPA]Br. Finally, the proposed mechanism was supported by the control experiments using other three ILs inhibitors and molecular dynamics simulation. Our work provided unique perspectives on developing rationally designed and efficient ILs inhibitors. [Display omitted] • Three novel dihydroxyl ionic liquids (DHILs) were synthesized. • DHILs facilitated the cementation of clay dispersion to enhance its thixotropy. • Both dihydroxyl and long alkyl chains highly improved the inhibition performance. • The proposed inhibition mechanism was verified via molecular dynamics simulation. [ABSTRACT FROM AUTHOR]

Increasing attention has been paid to the potential applications of biodegradable or natural surfactants in various fields, including chemical enhanced oil recovery (EOR), since the use of eco-friendly chemical processes was first proposed. The novel nonionic biosurfactant, ethoxylated phytosterols (BPS-n), was introduced to chemical EOR for the first time. The BPS-n showed a satisfactory ability to reduce the interfacial tension (IFT) between water and a model oil ( n -octane) when the effects of BPS-n concentration, salinity and temperature were investigated. Several typical alcohols have been used as cosurfactants to further reduce the IFT through synergistic effects with BPS-30. Interestingly, there may be a close relationship between the ability to reduce the IFT and the hydrophobic chain length of the alcohol. Based on the adsorption and stereo-hindrance effect, we proposed a reasonable explanation for this relationship. [ABSTRACT FROM AUTHOR]

Pickering emulsions are regarded as promising chemical flooding agents to control profile in enhanced oil recovery (EOR). Stimuli responsive Pickering emulsions are introduced to simplify the process of subsequent demulsification. In the present work, we construct pH and redox-triggered emulsions stabilized by oxidized 1,1′-ferrocenedicarboxylic acid-(N,N-dimethyldodecylamine) 2 (FDA-(DMDA) 2 -Ox) and Al 2 O 3 nanoparticles. Stable emulsions with low water separation rate (18.5 %) after 12-day storage can be obtained by combining a low concentration of FDA-(DMDA) 2 -Ox (< 0.07 wt%) and Al 2 O 3 nanoparticles. The emulsions can undergo the conversion of emulsion type (from oil-in-dispersion emulsions to oil-in-water Pickering emulsions) triggered by pH (surface charge switchability of Al 2 O 3 nanoparticles) and emulsification/demulsification switchable behaviors triggered by redox reaction (redox response of FDA-(DMDA) 2 -Ox). The switch mechanism is revealed via the measurements of optical micrographs, zeta potential, cyclic voltammetry curves, and interfacial tension. Micromodel tests display that both oil-in-dispersion emulsions and oil-in-water Pickering emulsions can improve the displacement efficiency and enhance the sweep efficiency respectively to greatly enhance oil recovery. The pH and redox responsive flooding fluid display promising adaptability to complicated reservoir conditions and convenient implement for subsequent demulsification, transportation and refining [Display omitted] [ABSTRACT FROM AUTHOR]

Stimuli responsive surfactants with reversible properties may effectively solve the problems of traditional surfactants (the switching of interfacial activity and the demulsification difficulty of emulsions) in enhanced oil recovery (EOR). In the present study, we fabricate brand-new redox-responsive double-tailed ferrocenyl surfactants 1,1′-ferrocenedicarboxylic acid-(N,N-dimethyldodecylamine) 2 (FDA-(DMDA) 2) via the dynamic supramolecular assembly. The reversible redox-responsive interfacial behaviors of ferrocenyl surfactants are estimated by measuring the interfacial tension reduction capacity, emulsifying performance, and wettability reversal ability. Compared with oxidized single-tailed ferrocenyl surfactant (FA-DMDA-Ox), oxidized double-tailed ferrocenyl surfactant (FDA-(DMDA) 2 -Ox) displays higher interfacial activity, which can be accurately switched by redox trigger. Cyclic micromodel flooding tests show that the FDA-(DMDA) 2 -Ox can in-situ emulsify the kerosene in pore media, and the addition of Na 2 SO 3 to the produced fluid can achieve the recycle of the surfactants. Oil displacement tests demonstrate that the developed double-tailed ferrocenyl surfactants possess the potential in EOR and recycling. [Display omitted] • Double-tailed ferrocenyl surfactants are fabricated via supramolecular assembly. • Double-tailed ferrocenyl surfactants show high interfacial activity. • The interfacial activity of surfactants can be switched by redox trigger. • The oxidized ferrocenyl surfactants can vastly enhance tertiary oil recovery. • The redox response can achieve the recycling of ferrocenyl surfactants. [ABSTRACT FROM AUTHOR]

The surfactant assisted nanoparticle stabilized emulsions exhibit the wide potential application and attract more and more attention. In the present study, the flake-like hydrophilic AlOOH nanoparticles were employed to stabilize Pickering emulsions with the assist of slightly amphiphilic sodium benzenesulfonate (SBS) molecules. The measurements of FTIR spectra, three-phase contact angle, zeta potential and Z-average diameter adequately testified the successful adsorption of SBS on AlOOH nanoparticles. Both slightly amphiphilic SBS and highly hydrophilic AlOOH nanoparticles could hardly stabilize emulsions, whereas the SBS modified AlOOH nanoparticles exhibited distinguished emulsifying capacity, which was reflected via the Turbiscan Stability Index and the reference values of backscattered light intensity. Batch adsorption experiments were conducted and the adsorption data was better fitted to the Langmuir model, suggesting that SBS could form monolayer adsorption on AlOOH nanoparticles. Confocal laser scanning microscopy and rheological measurements demonstrated that the functionalized AlOOH nanoparticles could spontaneously adsorb at the oil/water interface to form an interfacial film and generate a three-dimensional network structure in the continuous phase to effectively prevent droplet coalescence in normal and harsh conditions. Furthermore, SBS/AlOOH stabilized O/W emulsions presented significant displacement performance (tertiary oil recovery of 18.87%) in core flooding experiments. Microscopic visualization tests showed that the emulsions could block high permeability channels and enlarge the sweep area. This study opens up the possibility of adopting low surface-active molecules and hydrophilic nanoparticles to stabilize Pickering emulsions for enhanced oil recovery (EOR). [Display omitted] • Hydrophilic AlOOH nanoparticles are modified with slightly amphiphilic SBS. • Modified AlOOH nanoparticles show remarkable emulsifying capacity. • The SBS/AlOOH system exhibits excellent emulsion stability at harsh conditions. • The SBS/AlOOH stabilized Pickering emulsions display great potential to EOR. [ABSTRACT FROM AUTHOR]

Ionic liquids (ILs) have been introduced as novel high-performance shale inhibitors. The inhibition performance and mechanism of the cation groups in ILs have been widely investigated, whereas the effects of the anionic groups in ILs on the inhibitory capacity have rarely been reported. In this work, a series of fatty acid-based ionic liquids (FAILs) with different anionic groups, methyltrioctylammonium octanoate ([N 8881 ][C 8:0 ]), methyltrioctylammonium laurate ([N 8881 ][C 12:0 ]), and methyltrioctylammonium palmitate ([N 8881 ][C 16:0 ]), were synthesized to evaluate their inhibition ability via the sodium bentonite (Na-Bent) immersion test, the linear swelling test, and the shale hot-rolling recovery test. Compared with the traditional inhibitor KCl (2 wt%), FAIL [N 8881 ][C 8:0 ] showed greater inhibition performance at a much lower concentration (0.1 wt%). The inhibition mechanism of FAILs was further analysed by Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), zeta potential measurements, and contact angle measurements. It was speculated that the best inhibition ability and thermal stability of [N 8881 ][C 8:0 ] should be attributed to the intensive interaction and the size-matching effect between cationic and anionic groups. The present study provided novel insight into the research and development of high-efficiency shale inhibitors. [Display omitted] • FAILs exhibit great shale inhibition performances and thermal stability. • FAILs inhibit the clay swelling by electrostatic adsorption and hydrophobic shield. • The multiple cation/anion interaction in FAILs generate intensive adsorption layer. • The anionic group with optimal size-matching effect enhances the inhibition property. [ABSTRACT FROM AUTHOR]

Ionic liquids are regarded as the promising and efficient additives to use in various aspects of petroleum industry, especially in chemical EOR. In this investigation, three novel fatty acid ionic liquids (FAILs), methyltrioctylammonium octanoate ([N 8881 ][C 8:0 ]), methyltrioctylammonium laurate ([N 8881 ][C 12:0 ]) and methyltrioctylammonium palmitate ([N 8881 ][C 16:0 ]), were selected and evaluated for their performances in terms of surface/interfacial activity, temperature and salt resistances. The three FAILs could cause remarkable reduction of surface tension to ~30mN/m in their aqueous solutions, and the [N 8881 ][C 8:0 ] with the shortest anionic alkane chain exhibited the greatest surface activity among three FAILs. Then the size-match effect and intermolecular interaction were employed to explain the abnormal variations, which were confirmed by the control experiments using mixed surfactants and the molecular dynamics simulation. It was found that the binding energy in [N 8881 ][C 8:0 ] (−28.961 kcal/mol) was larger than that in [N 8881 ][C 16:0 ] (−22.942 kcal/mol), which should be responsible for their different surface activity. Moreover, the crude oil/water interfacial tension (IFT) could be decreased to the much level (4.9 ×10−3 mN/m and 1.7 × 10−2 mN/m) even at high-temperature conditions (80 °C) and at high-salinity conditions (100,000 mg/L), indicating the FAILs might be the ideal candidate for the EOR used surfactants with great temperature and salt tolerances. Meanwhile, the variations of IFT results further verified our proposed mechanism. [Display omitted] • FAILs exhibited the abnormal variation of surface/interfacial activity. • Both size-match and intermolecular interaction decide interfacial activity of FAILs. • Molecular simulation provides visual insight to the interfacial arrangement of FAILs. • FAILs possesses remarkable IFT reduction ability to ultralow level. • Great salt/temperature resistances of FAILs imply the promising application in EOR. [ABSTRACT FROM AUTHOR]

Both negatively charged SiO 2 nanoparticle and positively charged AlOOH nanoparticle have been widely used in various fields, including enhanced oil recovery (EOR). In this study, the mixed binary AlOOH/SiO 2 nanoparticle (MBN) systems are constructed and firstly employed in EOR. The measurements of zeta potential and Z-average diameter indicate that the stable MBN aqueous dispersion could be obtained by controlling AlOOH/SiO 2 mass ratios, which is quantificationally confirmed via the e-DLVO theory. Then the ternary TX-100-AlOOH-SiO 2 (TX-A-S) system exhibits the great ability to stabilize the emulsion at the much low nanoparticle concentration (0.15 wt% in total). The emulsion stability is further evaluated in the harsh conditions (high shear, temperature and electrolyte concentration). Moreover, core flooding and microscopic visualization experiments reflect the TX-A-S stabilized emulsion can dramatically enhance tertiary oil recovery (~23% of initial oil in place), which should be attributed to the high improvement of both displacement and sweep efficiency. [Display omitted] [ABSTRACT FROM AUTHOR]

Nanoparticles stabilized Pickering emulsions have been widely applied in various fields. The size and morphology of nanoparticles are regarded as crucial factors for the emulsion stability. In this study, the dendritic mesoporous silica nanoparticles (DMSNs) and two kinds of hybrid dendritic mesoporous silica titanium nanoparticles (DMSTNs-0.01 and DMSTNs-0.03) have been successfully prepared and investigated for their potential application to stabilize Pickering emulsions. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and UV-Vis diffuse reflectance spectra are employed to confirm the successful fabrication of the nanoparticles. The stability of DMSNs and DMSTNs stabilized emulsions are systematically evaluated via the optical microscopy and static multiple light scattering. The DMSTNs-0.01 displays the greatest ability to stabilize emulsions. N 2 physisorption and atomic force microscopy demonstrate the stability of Pickering emulsions is closely related to the specific surface area and surface roughness of nanoparticles. Moreover, DMSTNs-0.01 stabilized O/W Pickering emulsions show satisfactory displacement performance (tertiary oil recovery of 14.05%) in core flooding experiments. Microscopic visualization tests further indicate the emulsions can effectively block the high permeability channels generated by initial water flooding to increase the flowing resistance and then cause the flow diversion of the repellent fluid to enlarge the sweep area. [Display omitted] • Hybrid dendritic mesoporous silica titanium nanoparticles were prepared. • DMSTNs-0.01 exhibits excellent ability to stabilize emulsions at harsh conditions. • Specific surface area and surface roughness on emulsion stability was confirmed. • The fabricated hybrid silica titanium nanoparticles display great potential to EOR. [ABSTRACT FROM AUTHOR]

Abstract: Ribbon-like, wedge-shaped, and spherical gold nanostructures were prepared via a novel two-step growth method. Various gold nanostructures were first pre-formed in aqueous solution by using β-cyclodextrin (β-CD) as both reducing and capping agent. Due to the continuous growth of the pre-formed gold nanostructures at the air/water interface with the help of the Langmuir monolayers of 1-hexadecyl-3-methylimidazolium bromide (C16mimBr), morphology changes can be observed obviously. The gold nanostructures were characterized by transmission electron microscopy (TEM) and UV–vis spectroscopy. A possible mechanism based on the interaction between β-CD and the pre-formed gold nanostructures is proposed. [Copyright &y& Elsevier]

The Janus nanoparticles stabilized Pickering emulsions showed great application potential in various fields, including enhanced oil recovery (EOR). In this study, the amphiphilic Janus-SiO 2 nanoparticles (Janus-C12) are successfully synthesized by the Pickering emulsion method and characterized by Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), ζ-potential and contact angle measurements. The phase inversion from oil-in-water (O/W), multiple oil-in-water-oil (O/W/O) emulsion, to water-in-oil (W/O) emulsions was observed with the delicate control for the modification degrees of Janus-C12. The possible emulsification mechanisms for various Janus-C12 stabilized emulsions were proposed. The multiple O/W/O emulsion stability in harsh conditions and the influence factors (nanoparticles concentration, water/oil volume ratio and NaCl concentration) were studied systematically. Moreover, the Janus-C12–79% stabilized multiple O/W/O Pickering emulsions exhibited excellent EOR performance (additional oil recovery of 27.2%) in core flooding tests, and the possible EOR mechanism was explored via microscopic visualization experiments. [Display omitted] • Several amphiphilic Janus SiO 2 nanoparticles (Janus-C12) were synthesized. • The hydrophile-lipophile balance of Janus-C12 was accurately controlled. • The individual Janus-C12-79% could generate multiple O/W/O Pickering emulsions. • The O/W/O Pickering emulsions showed high displacement and great sweep efficiency. • Remarkable EOR performance was achieved by the O/W/O Pickering emulsion flooding. [ABSTRACT FROM AUTHOR]

Emulisons stabilized by surfactants have been used in enhanced oil recovery (EOR) for effective profile control and displacement, whereas the lack of long-term stability especially under harsh reservoir conditions limited their wide application. In this study, Pickering emulsions stabilized by sodium dodecylbenzenesulfonate (SDBS) and anisotropic slice-like AlOOH nanoparticles were systematically studied. The adsorption of SDBS on AlOOH nanoparticles was confirmed by the measurements of zeta potential and Fourier Transform Infrared (FTIR) spectra. The three-phase contact angle tests were conducted to explore the reason for the double phase inversion of the AlOOH/SDBS stabilized emulsions from o/w to w/o and back to o/w again. The optical microscopy images verified the adsorption mechanism of SDBS on AlOOH nanoparticles at the oil/water interface. It was found that the three-dimensional network structure formed by the micro-flocculated modified AlOOH nanoparticles could prevent coalescence and phase separation, resulting in the enhanced stability of the emulsion. The AlOOH/SDBS stabilized emulsion showed the super tolerances in a wide range of shear rates, temperature and electrolyte concentrations. The core flooding tests and microscopic visualization flooding experiments demonstrated that the AlOOH/SDBS stabilized emulsions significantly improved the tertiary oil recovery (33 % of IOIP) via the enhanced displacement and sweep efficiencies. The present study provides a typical Pickering emulsion with great stability under harsh reservoir conditions for EOR. [ABSTRACT FROM AUTHOR]

• The ZnO NPs could further reduce the IFT in the mixed surfactants/NPs system. • DDAB molecules could adsorb on ZnO NPs and tend to form hemimicelles. • The modified NPs prefer synergizing with surfactants to further reduce the IFT. • DDAB adsorption processes with and without ZnO NPs are controlled by the DKC model. We systemically evaluated the effects of the additional ZnO nanoparticles (NPs) on the interfacial activity of the cationic surfactant didodecyldimethylammonium bromide (DDAB) with two hydrophobic chains by the interfacial tension (IFT) measurement and emulsification experiments. The addition of ZnO NPs greatly improved the interfacial activity of the mixed ZnO/DDAB system at the oil/water interface. The zeta potential and fluorescence spectra of the mixed ZnO/DDAB dispersions were investigated to explore the adsorption behavior of DDAB molecules on ZnO NP surfaces. The IFT between a homologous series of n-alkanes and DDAB aqueous solutions in the absence and presence of ZnO NPs was measured to explore the mechanism of the further IFT reduction caused by the additional ZnO NPs. The dynamic IFT data were fitted with two different models. The results indicated that the DDAB adsorption processes in the absence and presence of ZnO NPs were controlled by the mixed diffusion-kinetic controlled model. [ABSTRACT FROM AUTHOR]

Highlights: [•] The assembly process of gold nanoparticles is controlled by surfactant structures. [•] The distribution fashion of capping agent is the key factor for the gold nanochains. [•] Systems with mixed nonionic surfactants were further investigated. [•] The different capping fashions transform gold nanochains into single nanoparticles. [•] The diverse capping fashions interpret the different stabilities of nanostructures. [ABSTRACT FROM AUTHOR]

With the widespread application of polymer flooding technology in oilfields, the high performance and eco-friendly polymer is urgently needed to meet the sustainable oilfield development. The hydrophobic modified carboxyl nanocellulose (TCCNF) have caught the attention of many researchers. In this paper, the alkyl chains, benzene rings and their mixed modification groups are grafted to TCCNF to investigate the influences of different hydrophobic modification groups on the enhancing oil recovery (EOR) related properties of TCCNF. The results of interfacial tension (IFT) measurement, the TURBISCAN Lab stability analysis and the viscosity measurement show that the mixed modified TCCNF exhibits the best interfacial activity and emulsification viscosity reduction ability, which is due to the synergistic effect between grafted alkyl chains and benzene rings. Then the molecular dynamics (MD) simulation is used to further demonstrate the synergistic effect by studying the adsorption of different modified TCCNF at the crude oil/water interface and interaction with multifarious constituents of crude oil. And the core flooding tests confirm the possible application of the hydrophobic modified TCCNF in EOR. This work presents the novel insights to the effects of different modification groups on the EOR related properties of TCCNF at the crude oil/water interface. [Display omitted] • The effects of modification groups on property of nanocellulose were verified. • The hydrophobic groups enhanced the EOR related properties of nanocellulose. • There were different interactions between different graft groups and crude oil. • The synergistic effect of mixed grafted groups was illustrated by MD simulation. [ABSTRACT FROM AUTHOR]

The typical organic salt benzyltrimethylammonium bromide (BMAB) was used to greatly enhance the interfacial activity of the traditional anionic surfactant sodium dodecyl benzene sulfonate (SDBS). The additional BMAB caused the obvious reduction of the interfacial tension (IFT) between the SDBS aqueous solution with a low concentration and model oil (V toluene :V n-decane  = 1:1). Based on the special SDBS/BMAB intermolecular interaction, we proposed that the synergistic effect between the electrostatic attraction and π-π stacking interaction largely increased the SDBS interfacial concentration, leading to the dramatic IFT reduction. Three organic salts and two surfactants with similar structures, as well as the typical inorganic salt NaCl, were used in control experiments to confirm our speculation. The interaction energies between SDBS molecules and different organic salts were calculated using molecular mechanics to further interpret the mechanism. The salt and temperature tolerances of the SDBS/BMAB system were systematically investigated. Moreover, the availability of the SDBS/BMAB mixture in brine water/crude oil system was evaluated by the core flooding tests. [ABSTRACT FROM AUTHOR]