•The viscosities of the different concentrations of the TVP is increased above the Tcass with the increase of temperature.•With the increase of temperature from 30 °C to 90 °C, the shear viscosities of different concentrations of the TVP showed shear thickening behavior.•The 700 mg/L concentration of the novel TVP compared with a 3500 mg/L concentration of HPAM under same conditions showed good viscoelastic properties.Polymer flooding is one of the most effective processes to enhance oil recovery (EOR), but the poor thermo-stability and salt tolerance of the currently used water-soluble polymers challenge their usage in presence of high temperatures and salinity within the oil reservoirs. Thermo-viscosifying polymers (TVP’s) are a novel class of materials developed for EOR applications in high-temperature and high-salinity oil reservoirs. In this study, the interactions of novel TVP with different salts and its temperature and rheological properties were evaluated. The thermal and rheological properties of this polymer were studied as a function of polymer concentration, and salinity at different temperatures. It was observed that by increasing temperature, the aqueous solution viscosities first smoothly decreased, but then increased at above the critical association temperature (Tcass). Tcass was also found to be a function of the TVP’s concentration and temperature. Although, the shear effect demonstrated shear-thinning, with the increase of temperature, the shear viscosities showed shear thickening at all concentrations of polymer. Furthermore, the novel TVP with low concentration showed good viscoelastic properties compared with high concentration of HPAM. The introduced novel TVP’s thermo-thickening tendency is enhanced by increasing temperature and salinity which makes it more promising for EOR applications.Download high-res image (119KB)Download full-size image

This study systematically reports the rheological behaviour and mechanism for mixtures of cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and anionic–nonionic carboxylate surfactants (NPEC-n). The effects of molar ratio, total concentration, salinity, shearing time, temperature, and ethylene oxide (EO) moieties on the microstructures of the mixtures were investigated in detail using rheometry, freeze-fracture transmission electron microscopy (FF-TEM), cryo-transmission electron microscopy (Cryo-TEM), etc. The results indicate that the conformations of the EO moieties concern the head-group areas and steric hindrance, which affect the arrangement of the surfactant molecules. The aggregates with diverse morphologies endow the solutions with different rheological behaviours. Except for the CTAB/NPEC-10 system, the CTAB/NPEC-5 system and CTAB/NPEC-7 system show viscoelastic behaviour under some conditions and their highest viscosities appear at the molar ratio of 76 : 24 and 40 : 60, respectively. The transition temperature of the mixture appears at 35 °C, accompanied with a sharp decrease in the viscosity. The salt thickening and shear-resistant properties of the mixtures have also been discussed, indicating good salt-resistance and shear-resistance of the mixtures.

To investigate the contribution of hydrophobic groups of hydrophobically modified polyacrylamide (HMPAM) to stabilizing crude oil emulsion, the β-cyclodextrin (β-CD) inclusion method based on host–guest interaction is proposed. Dynamic light scattering is employed to study the stability of O/W emulsions prepared by HMPAM and inclusion complexes. The emulsions are evaluated in terms of droplet size distribution, rheological properties and interfacial tension. It is found that the stability of emulsions stabilized by HMPAM decreases with the increase of β-CD, indicating that β-CD can effectively shield the hydrophobic groups in the emulsification process of crude oil through the formation of an inclusion complex. Consequently, the network structure composed of associated amphiphilic polymers is destroyed, resulting in released polymer molecules with none of the hydrophobic groups. Moreover, the emulsion stabilizing mechanism of HMPAM with different β-CD amounts is discussed. Based on Turbiscan Stability Index (TSI) analysis, the contribution degree of the hydrophobic group of HMPAM in stabilizing emulsions (ECh) is determined for the first time. The emulsifying ability of amphiphilic polymers is mainly attributed to the hydrophobic groups (ECh > 80%) of the amphiphilic polymers while the concentration of HMPAM is above the critical aggregation concentration (CAC). This research provides theoretical guidance for studying the emulsification and de-emulsification mechanism of emulsions stabilized by amphiphilic polymers which are widely applied in tertiary oil recovery.

•Bundled aggregates form in cationic/anionic surfactants mixtures with specific concentrations.•Aggregates transformations occur with an increasing temperature, from bundled aggregates to wormlike micelles or smaller-sized micelles.•The mixed solutions show various rheological behaviors, including anisotropic non-Newtonian fluid, viscoelastic fluid and Newtonian fluid.Thermally-induced formation of wormlike micelles (WLMs) in mixed surfactant solutions is investigated. The mixtures are composed of cationic surfactant cetyltrimethyl ammonium bromide (CTAB) and anionic surfactant sodium dodecyl sulfate (SDS). The rheological characteristics, thermal curves and transmittance spectrum are obtained with Rheometer, differential scanning calorimeter (DSC) and TURBISCAN Lab stability analyzer, respectively. The Arrhenius equation is introduced to calculate the activation energy. Microscopic observation is captured with freeze-fracture transmission electron microscope (FF-TEM) at various temperatures. The results reveal that the zero-shear viscosity of the mixed solutions fluctuates at 20 °C −50 °C and a specific thermal-thickening phenomenon occurs in the aforementioned temperature range. When the temperature reaches 35 °C, the rheological properties of the mixed solution behave distinctly compared with those beyond 35 °C. There are two endothermic peaks in the DSC curve and a dramatic change in the transmittance spectrum. The FF-TEM microscopic images show that the bundled anisotropic aggregates convert into WLMs as the temperature increases from 20 °C to 40 °C. This study reveals that the transformation of aggregates is induced by temperature. Moreover, the WLMs form during the process of temperature elevation as is proved by the rheological behavior, FF-TEM microscopic images and the activation energy (236.5 KJ mol−1). The current study also suggests a simple approach to obtain the WLMs at accurate temperatures.Aggregates transformations occur with an increasing of the temperature, leading to a fluctuation in viscosity.Download high-res image (169KB)Download full-size image

•The viscosity of polymer is increased at high concentrations of salt.•With increase concentrations of salt at high salinities the structure of polymer formed network structure.•At high temperatures the 1000 mg/L and 1100 mg/L concentrations showed thickening properties.The influence of salt and temperature on the viscosity of a hydrophobically modified polyacrylamide-based (PAM-based) novel functional polymer (RH-4) was investigated. To study the viscosifying mechanism in brine solution, scanning electron microscope (SEM) was applied to observe the network microstructures of polymer solution. The solution apparent viscosity behaviors of the RH-4 polymer are studied as functions of concentrations, pH value, salt types and amount, microscopic morphology. The viscoelasticity of aqueous solutions of RH-4 polymer changed with shear rate under high salinity condition. Additionally, the influence of temperature on the apparent viscosity of RH-4 polymer was investigated. The results showed that the viscosity decreased at lower salt concentrations and increased at higher salt concentrations. The SEM results show that the network structures of RH-4 polymer become much more condense at high salinity, which lead to the increasing its apparent viscosity. When the salinity reaches 80,000 mg/L, thickening ability of the system is the strongest. With the rise in temperature, the viscosity of polymer solutions with various concentrations decreases slightly except for the two concentrations of 1000 mg/L and 1100 mg/L, their viscosity increases with the increasing of temperature. The thickening tendency is enhanced by high salinity and high temperature, which makes it more promising for EOR.Download high-res image (133KB)Download full-size image

•The prepared viscoelastic microspheres are spherical particles with particle size of 100.6μm.•The viscoelastic microspheres with 3-D network structure have good swelling capability.•The dispersed system shows shear-thickening behavior under certain conditions.•The energy dissipation behaviors of the dispersed system were studied in the energy point.Dispersed viscoelastic microsphere systems have preliminarily been applied in oil fields with gratifying successes. In this paper, a type of viscoelastic microsphere system with an average particle size of 100.6 μm was synthesized by employing the inverse suspension polymerization. The synthesized viscoelastic microspheres could swell 25.42 times due to the three-dimension structure. The rheological properties of dispersed viscoelastic microsphere system were researched by dynamic strain amplitude scanning measurements and the energy dissipation behaviors were investigated through mathematical method. The results showed that the dispersed system exhibited “shear-thickening” behavior when the strain was greater than the critical strain at different fixed angular frequency. The area enclosed by LISSAJOUS curves or normalized LISSAJOUS curves increased with the increasing of the strain at fixed angular frequency. The relationship between the dissipated energy (Ed) and strain amplitude (γmax) is: Ed = K(γmax)α. And the relationship between the dissipated energy exponent (α) and the fixed angular frequency(ω) is: α∝ω0.131±0.009. Therefore, as the strain increases, the clusters grow up gradually and block the flow of the system, which results in “shear-thickening” and the demand of additional energy.The energy dissipation behavior was indicated by the area enclosed by normalized LISSAJOUS.

•The host–guest inclusion complex has a good thickening performance.•The complex solution has strong resistance to salt, temperature, shearing and pH.•The complex O/W emulsion is more stable than the single P(AM/C18/NaA)’s.•The stability mechanism of emulsion was indicated by three-stage visual rheology.A supramolecular recognition system was constructed based on the host–guest interaction with water-soluble β-cyclodextrinpolymer-P(AM/A-β-CD/NaA) as the host polymer and hydrophobically modified polyacrylamide-P(AM/C18/NaA) as the guest one. The guest polymer contains a small amount of hydrophobic octadecyl groups. High viscosity enhancement was observed when P(AM/A-β-CD/NaA) was added to P(AM/C18/NaA) solution, the concentration of P(AM/C18/NaA) was under the critical aggregation concentrations (CAC), as a result of the polymer inclusion association. The influences of salt concentration, shearing, pH values and temperature on the viscosity of mixture solution were also studied. O/W crude oil emulsion stabilized by the complex was prepared. A laser particle size analyzer and Turbiscan Lab Expert stability analyzer were employed to study their stability. The results indicated that mixture emulsion became more stable than the single amphiphilic polymer's. This is because that the net structure of elastic polymer in the continuous phase has the ability to hold oil droplets at the low concentration of P(AM/C18/NaA). The stability mechanism of O/W emulsion was indicated by three-stage visual rheological method. In this paper, the stability of inclusion complex is discussed, and the mechanism of the enhanced oil emulsification is further explored.The stability study of O/W emulsion was indicated by backscattering and three-stage visual rheological method.