Interaction between polymer and anionic/nonionic surfactants and its mechanism of enhanced oil recovery

Molecular Dynamics Simulation of the Effects of Anionic-Nonionic Surfactants on Interfacial Properties of the Oil-Water Interface

Surfactant oil drive is a crucially enhanced oil recovery method that improves oil recovery rates. The aggregation behavior of surfactant molecules at the oil-water interface significantly influences oil repulsion. In this study, a molecular dynamics simulation is used to investigate this repellent behavior of single and binary surfactants of alkanolamides (6501) and fatty alcohol polyoxyethylene ether sodium sulfate (AES). The oil-water interface is characterized by density distribution, interfacial thickness, radial distribution function, interfacial tension, and interfacial generation energy. The results reveal that the dodecanolamide surfactant (126501) and AES effectively reduce interfacial tension. In the binary 126501/AES system, the interfacial film thickness increases to 18.08 Å, and the diffusion coefficient increases to 0.186 Å2/ps. The radial distribution function shows that oil molecules are located 4.2 Å from the anionic head of AES, which weakens the intermolecular forces within the oil layer. In the 126501/AES system, the interfacial energy of -96.12 kJ/mol indicates a stable interface. Moreover, both the 126501/AES and tetradecanolamide surfactant (146501)/AES systems exhibit excellent resistance to metal ions. The molecular-level mechanism provides useful guidance for designing the surfactant systems for enhanced oil recovery.

The Synergistic Effects between Sulfobetaine and Hydrophobically Modified Polyacrylamide on Properties Related to Enhanced Oil Recovery

In order to explore the mechanism responsible for the interactions in the surfactant-polymer composite flooding and broaden the application range of the binary system in heterogeneous oil reservoirs, in this paper, the influences of different surfactants on the viscosity of two polymers with similar molecular weights, partially hydrolyzed polyacrylamide (HPAM) and hydrophobically modified polyacrylamide (HMPAM), were studied at different reservoir environments. In addition, the relationship between the surfactant-polymer synergistic effects and oil displacement efficiency was also investigated. The experimental results show that for HPAM, surfactants mainly act as an electrolyte to reduce its viscosity. For HMPAM, SDBS and TX-100 will form aggregates with the hydrophobic blocks of polymer molecules, reducing the bulk viscosity. However, zwitterionic surfactant aralkyl substituted alkyl sulfobetaine BSB molecules can build "bridges" between different polymer molecules through hydrogen bonding and electrostatic interaction. After forming aggregates with HMPAM molecules, the viscosity will increase. The presence of two polymers all weakened the surfactant oil-water interfacial membrane strength to a certain extent, but had little effect on the interfacial tension. The synergistic effect of the "bridge" between HMPAM and BSB under macroscopic conditions also occurs in the microscopic pores of the core, which has a beneficial effect on improving oil recovery.

Adsorption Characteristics of Ionic Surfactants on Anthracite Surface: A Combined Experimental and Modeling Study

Ionic surfactants are widely used in coal dust control in mines, and their adsorption characteristics on the coal surface have a great influence on the coal dust control effect. In this investigation, anionic sodium dodecylbenzenesulfonate (SDBS) and cationic octadecyltrimethylammonium chloride (STAC) were selected to explore the adsorption characteristics of ionic surfactants on the surface of anthracite. The experimental results show that the adsorption rate and efficiency of STAC on the surface of anthracite are higher than that of SDBS; STAC can form a denser surfactant layer on the surface of anthracite, with a larger adsorption capacity and higher strength. Molecular dynamics simulations show that the adsorption between STAC and the surface of anthracite is tighter, and the distribution at the coal–water interface is more uniform; the surface of anthracite modified by STAC has a stronger binding ability to water molecules.

Characterization of Hydrophobically Modified Polyacrylamide in Mixed Polymer-Gemini Surfactant Systems for Enhanced Oil Recovery Application

The study deals with the synthesis and characterization of the hydrophobically modified polyacrylamide (HMPA) copolymer and its functional property evaluation in mixed polymer-gemini surfactant systems for application in enhanced oil recovery (EOR). The copolymer was initially prepared in the laboratory using acrylamide and N-phenylacrylamide monomer units via an addition polymerization route. The synthesized copolymer was characterized by Fourier transform infrared and proton nuclear magnetic resonance to identify suitable functional groups in the compound. Gel permeation chromatography tests showed that the polymer has a molecular weight of 2.098 × 10⁵ Da. Copolymer solution showed favorable tolerance to variations in temperature and salinity. Salt precipitation studies identified tolerance limit up to 25% NaCl at a temperature of 343 K. Viscosity of HMPA fluids showed an increase with increasing concentration. Interestingly, salt addition until 1.0% NaCl showed an increase in solution viscosity owing to the electrostatic shielding of the HMPA polymer and strengthened intermolecular association of the hydrophobic groups. This behavior is against physicochemical properties observed in the case of conventional polymers but exhibits promising functionality in EOR processes wherein better oil mobility control is desired under subsurface conditions. Gemini surfactants accommodate onto "vacant adsorption" sites onto the liquid surface, improving the interfacial adsorption property and reducing surface tension. In the presence of gemini surfactant polymers forming mixed nanoemulsion fluid systems with favorable pseudoplastic character, their viscosities initially increase with surfactant concentration due to binding of surfactant molecules to hydrophobic junctions of polymer chains to form mixed micelles. Eventually, polymer hydrophobes get saturated with surfactant micelles, and viscosity decreases due to electrostatic repulsion among surfactant micelles. Dynamic light scattering analyses confirmed the formation of nanoemulsion droplets with sizes of <310 nm in the case of {surfactant + copolymer} encapsulation. Zeta potential measurements showed that an increase in 14-6-14 gemini surfactant concentration enhanced the stability of nanoemulsion fluid due to increasing zeta potential values. However, the nonionic SF-6-SF surfactant does not affect the zeta potential of nanoemulsions. Surfactant addition reduced the oil-aqueous interfacial tension of polymer solutions to several magnitudes of an order of 10^-1 to 10^-2 mN/m. Contact angle studies identified the ability of the polymer as well as polymer-surfactant nanoemulsions to alter the wettability of the reservoir rock from the intermediate-wet (90°-120°) to strongly water-wet state (<20°) at different temperatures. Analyzed formulations showed favorable miscibility with crude oil at 343 K. In summary, HMPA/gemini surfactant-based emulsions possess promising physicochemical and stabilization attributes for application in EOR.

Influence of Ethylene Oxide Content in Nonionic Surfactant to the Hydrolysis of Reactive Dye in Silicone Non-Aqueous Dyeing System

Silicone reverse dyeing technology provides an important means of saving water and salts-free in the textile dyeing industry. The interactions between dyes and surfactants may influence the hydrolysis of dye during dyeing. In this investigation, the effect of ethylene oxide content in nonionic surfactant on the hydrolytic reaction of reactive dye was firstly investigated in a siloxane reverse emulsion dyeing system. Compared with no surfactants, the hydrolytic reaction of vinyl sulfone reactive dye was a slowdown when some nonionic surfactants were used during dyeing. Usually, the hydrophobic groups in nonionic surfactants were dodecyl chains but their polar head groups were different. The hydrolytic reaction of vinyl sulfone dye showed that the longer of EO (ethylene oxide) chains, the faster the hydrolytic reaction of vinyl sulfone dye. From the absorption spectrum of dye, it could be concluded that more of dyes would be solubilized into the formed micelles, and dye-surfactant complexes were adhered to the surface of micelles if the molecular structure of surfactant had a shorter EO chains. Furthermore, the intramolecular or intermolecular hydrogen bond could be formed between dye and surfactant, which would further influence the hydrolytic reaction of vinyl sulfone dye. However, the solubility of surfactant in siloxane non-aqueous media would decrease with the increase of EO chains. Meanwhile, the dispersion of dye was enhanced as well as the hydrolytic reaction of dye. From this investigation, some surfactant can be used to improve the fixation of reactive dye during dyeing. Furthermore, washing times after dyeing and the ecological problems can be decreased.