Xia Yin

pH-Responsive wormlike micelles based on microstructural transition in a C22-tailed cationic surfactant–aromatic dibasic acid system

pH-Responsive wormlike micelles based on microstructural transition, and formed by complexation of N-erucamidopropyl-N,N-dimethylamine (UC22AMPM) and potassium phthalic acid (PPA) at a molar ratio of 2 : 1, were developed and compared with CTAB/PPA at the same molar ratio. Phase behavior, viscoelasticity, and microstructural transitions of solutions were investigated by observing their appearance, rheological characteristics, dynamic light scattering, and 1H NMR measurements. It was found that the phase behavior of UC22AMPM/PPA solutions undergoes transitions from transparent viscoelastic fluid to phase separation with white floaters upon increasing pH. By increasing pH from 2.01 to 6.19, the viscosity of wormlike micelles in the transparent solutions continuously increased and reached ∼1.4 × 106 mPa s at pH 6.19. As pH was adjusted to 7.32, the opalescent solution showed a water-like flowing behaviour and the η0 rapidly declined to ∼1.7 mPa s. The viscosity of the CTAB/PPA solutions had a maximum at pH 2.98 and then decreased with increasing pH. This radical variation in rheological behavior is attributed to the pH dependent hydrophobicity of PPA and ultra-long hydrophobic chain of UC22AMPM. Additionally, dramatic viscosity changes of about 6 magnitudes can be triggered by varying pH without any deterioration for the UC22AMPM/PPA system.

Thickening behavior and synergistic mechanism of mixed system of two hydrophobically associating polymers

ABSTRACT The thickening behavior and synergistic mechanism of the mixed system of the hydrophobically associating polymer (HAP-S) (acrylamide/acrylate-EOm-POn/sodium acrylate terpolymer) with small molecular weight and the acrylamide/N-isooctyl acrylamide/sodium acrylate terpolymer (HAP-L) with large molecular weight were investigated via the rheology, inclusion action of β-cyclodextrin (β-CD), cohesive energy, dynamic light scattering (DLS), and scanning electron microscope (SEM). The apparent viscosity of the mixed-system solution was higher than that of the HAP solution alone in a wide range of mass ratios and concentrations of the two polymers, ascribing to the enhancement of associated viscosity and strength of the network structure by forming mixed aggregates and bridging among them. Furthermore, the hydrodynamic radius of the mixed-system aggregates increased due to the improved network structure and the electrostatic repulsion effect among the different kinds of HAP molecules. Under the synthetical influence of the above-mentioned factors, the mixed system displayed better temperature resistance and salt tolerance as compared to the HAP solution alone. GRAPHICAL ABSTRACT

Study on salt thickening mechanism of the amphiphilic polymer with betaine zwitterionic group by β-cyclodextrin inclusion method

A method based on host-guest inclusion system was used to investigate the salt thickening mechanism of poly [acrylamide-co-N, N′-dimethyl (methylmethacryloyl ethyl) ammonium propane sulfonate-co-cetyl dimethyl allyl ammonium chloride] (PADC). The salt thickening behavior of PADC solution was studied by rotational viscometer, and its average hydrodynamic diameter (Dh) was characterized by dynamic light scattering (DLS). The formed host (β-cyclodextrin)-guest (hydrophobic groups of PADC) inclusion system was confirmed by scanning electron microscopy (SEM). A method of characterizing the hydrophobic association strength and determining the hydrophobic association contribution rate (HACR) was introduced by the inclusion of β-cyclodextrin (β-CD). The results showed that the apparent viscosity and the Dh of PADC solution increased with the increase of salt concentration. In addition, the types of salt also affected the thickening property of PADC solution. Moreover, the results of HACR indicated that the hydrophobic association strength of PADC solution was enhanced in the presence of salts, which was confirmed by fluorescent method. Thus, it could be concluded that the salt thickening of PADC solution was caused by the destruction of ionic bonds in betaine monomer and the enhancement of hydrophobic association strength.

Synthesis and plugging behavior of fluorescent polymer microspheres as a kind of conformance control agent in reservoirs

The fluorescent polymer microsphere is a newly developed chemical agent for conformance control in reservoirs. In this paper, one kind of fluorescent polymer microspheres P(AM-BA-RhB) was synthesized via the inverse suspension polymerization method with Rhodamine B as a fluorescence functional monomer. Laboratory experiments were performed to characterize the morphology, fluorescent property, swelling property and plugging behavior of fluorescent polymer microspheres. The experimental results showed that the polymer microspheres P(AM-BA-RhB) displayed stable fluorescence performance in solutions containing metal ions at pH values between 3.0 and 10.0. The swelling property was not dramatically affected by the Rhodamine B embedded in the polymer microspheres by grafting. Both a visual micromodel test and sand-pack tubes experiment demonstrated that the fluorescent polymer microspheres could pass directly or by deformation through porous media and get into the in-depth formation. The injection pressure showed the phenomenon of “Wave-type Variation”. Three plugging behaviors such as piston plugging, protruding plugging and fingering plugging were put forward. The introduction of fluorescent polymer microspheres could provide one method to research the conformance control and EOR mechanism of polymer microspheres in the reservoirs.

Demulsifier performance at low temperature in a low permeability reservoir

ABSTRACT The crude oil in Longdong area is produced in the form of emulsion containing associated oil and water, which needs to be separated before dispatch to end user. Chemical demulsification under high temperature is the most widely used technology to break the emulsions. In this study a rheological method was used to determine the curve of viscosity-temperature and lower limit of temperature was determined. A series of experiments on low-temperature commercial demulsifies were implemented for studying demulsification performance by bottle test method. Mechanism of low-temperature demulsifier was studied by using spinning drop interfacial tensiometer to determine interfacial tension between the crude oil and demulsifier solution by considering the concentration. Turbiscan stability analyzer was used to study the effect of water content, temperature, and demulsifier concentration on emulsion stability. The corresponding relationship between interfacial tension and demulsification was verified through the study of low-temperature demulsifier effect on interfacial tension. Efficient low-temperature demulsifiers AR102, AR901, PR929, and PRC06 were selected. PRC06 was chosen to be the best at 40°C, and when the optimal concentration was 200 mg/L, dehydration rate was 99.51%.

Effect of different molecular weight amphiphilic polymers on emulsifying behavior

Abstract Amphiphilic polymers applied in oil fields are polymer mixtures with different molecular weight. Stability of O/W emulsion prepared by amphiphilic polymers with different molecular weight was studied by stability analyzer. The difference in stability was clarified according to the external phase and interfacial properties. Results showed that PI(micro-molecular polymer) formed a tighter network structure in solution which exhibit higher viscoelasticity and more resistant to shear; and was more favorable to the emulsion stability than PII(macro-molecular polymer) due to higher surface activity. This work provides references for the molecular weight distribution optimization of amphiphilic polymer.