Yifei Liu

Investigation of Novel Triple-Responsive Wormlike Micelles

Smart wormlike micelles with stimuli-tunable rheological properties may be useful in a variety of applications, such as in molecular devices and sensors. The formation of triplestimuli-responsive systems so far has been a challenging and important issue. In this work, a novel triplestimuli (photo-, pH-, and thermoresponsive) wormlike micelle is constructed with N-cetyl-N-methylmorpholinium bromide and trans-cinnamic acid (CA). The corresponding multiresponsive behaviors of wormlike micellar system were revealed using cryogenic transmission electron microscopy, a rheometer, and 1H NMR. The rheological properties of wormlike micellar system under different temperatures, pH conditions, and UV irradiation times are measured. As confirmed by 1H NMR, chemical structure of a CA molecule can be altered by the multiple stimulation from an exotic environment. We expect it to be a good model for triple-responsive wormlike micelles, which is helpful to understand the mechanism of triple-responsiveness and widen their applications.

The first study of surface modified silica nanoparticles in pressure-decreasing application

In this study, hydrophobic silica nanoparticles were prepared by the surface modification of silica nanoparticles using dimethyldichlorosilane. Fourier transform infrared spectroscopy, thermogravimetric analysis, and X-ray photoelectron spectroscopy were employed for the characterization of the raw silica nanoparticles and modified silica nanoparticles. The results showed that methyl groups are successfully grafted on the surface of silica nanoparticles. The titration method was employed to quantitatively determine the surface hydroxyl number of silica nanoparticles; the result demonstrated that the surface hydroxyl number of silica nanoparticles significantly decreases after modification. The modified silica nanoparticles was dispersed in water using TX-100 as the dispersant and NaOH to adjust the pH. The dispersion was injected into an oil-treated artificial core, the injecting pressure of the NaCl solution (5 wt%) before and after injection was measured. The result showed that the hydrophobic silica nanoparticles exhibit a good pressure-decreasing ability. The contact angle of the slabbed core was measured, the contact angle increased from 36° to 134° after it was treated by the modified silica nanoparticle dispersion. Transmission electron microscopy was employed for the characterization of the modified silica nanoparticles. Scanning electron microscopy was employed for the characterization of the treated core; the result showed that the modified silica nanoparticles are adsorbed on the surface of the core and forms a hydrophobic layer, changing the wettability of the sand surface from water wet to oil wet, thereby decreasing the flowing pressure.

Thermal and pH dual stimulated wormlike micelle in aqueous N-cetyl-N-methylpyrrolidinium bromide cationic surfactant-aromatic dibasic acid system

Dual-stimulated wormlike micelles regulated by pH and temperature in a surface active ionic liquid system comprising of a cationic surfactant (N-cetyl-N-methylpyrrolidinium bromide (C16MDB)) and an aromatic dibasic acid (pyrocatechol) were investigated. Such a system can be reversibly switched between liquid-like and gel-like states on adjusting the solution pH value. The rheology, light scattering techniques and cryogenic-transmission electron microscopy (cryo-TEM) results show the growth of spherical micelles into long and entangled wormlike micelles was responsible for the changes in flow properties such as high viscosity, shear-thinning behaviour and Maxwell-type dynamic rheology. The nuclear magnetic resonance results reveal the binding capacity of pyrocatechol to C16MDB is proposed as the key factor of the unusual rheological and micellar responses of this pH-stimulated system. In addition, with the increase of temperature, molecular motion of surfactant molecules becomes more active, which endow the property of thermo-stimulated to the surface active ionic liquid system.

Study on the reutilization of clear fracturing flowback fluids in surfactant flooding with additives for Enhanced Oil Recovery (EOR).

An investigation was conducted to study the reutilization of clear fracturing flowback fluids composed of viscoelastic surfactants (VES) with additives in surfactant flooding, making the process more efficient and cost-effective. The clear fracturing flowback fluids were used as surfactant flooding system with the addition of α-olefin sulfonate (AOS) for enhanced oil recovery (EOR). The interfacial activity, emulsification activity and oil recovery capability of the recycling system were studied. The interfacial tension (IFT) between recycling system and oil can be reduced by 2 orders of magnitude to 10−3 mN/m, which satisfies the basic demand of surfactant flooding. The oil can be emulsified and dispersed more easily due to the synergetic effect of VES and AOS. The oil-wet surface of quartz can be easily converted to water-wet through adsorption of surfactants (VES/AOS) on the surface. Thirteen core plug flooding tests were conducted to investigate the effects of AOS concentrations, slug sizes and slug types of the recycling system on the incremental oil recovery. The investigations prove that reclaiming clear fracturing flowback fluids after fracturing operation and reuse it in surfactant flooding might have less impact on environment and be more economical.

Study of the formation and solution properties of worm-like micelles formed using both N-hexadecyl-N-methylpiperidinium bromide-based cationic surfactant and anionic surfactant.

The viscoelastic properties of worm-like micelles formed by mixing the cationic surfactant N-hexadecyl-N-methylpiperidinium bromide (C16MDB) with the anionic surfactant sodium laurate (SL) in aqueous solutions were investigated using rheological measurements. The effects of sodium laurate and temperature on the worm-like micelles and the mechanism of the observed shear thinning phenomenon and pseudoplastic behavior were systematically investigated. Additionally, cryogenic transmission electron microscopy images further ascertained existence of entangled worm-like micelles.

Aggregation behavior of long-chain piperidinium ionic liquids in ethylammonium nitrate.

Micelles formed by the long-chain piperidinium ionic liquids (ILs) N-alkyl-N-methylpiperidinium bromide of general formula CnPDB (n = 12, 14, 16) in ethylammonium nitrate (EAN) were investigated through surface tension and dissipative particle dynamics (DPD) simulations. Through surface tension measurements, the critical micelle concentration (cmc), the effectiveness of surface tension reduction (Πcmc), the maximum excess surface concentration (Гmax) and the minimum area occupied per surfactant molecule (Amin) can be obtained. A series of thermodynamic parameters (ΔGm0, ΔHm0 and ΔSm0) of micellization can be calculated and the results showed that the micellization was entropy-driven. In addition, the DPD simulation was performed to simulate the whole aggregation process behavior to better reveal the micelle formation process.

Investigation on the aggregation behavior of photo-responsive system composed of 1-hexadecyl-3-methylimidazolium bromide and 2-methoxycinnamic acid

A novel fluid system composed of 2-methoxycinnamic acid (trans-OMCA) and 1-hexadecyl-3-methylimidazolium bromide (C16mimBr) in an aqueous solution was investigated. The compounds trans-OMCA and C16mimBr in an aqueous solution can self-assemble and form viscoelastic worm-like micelles. The concentrations of trans-OMCA and C16mimBr have a significant influence on the rheological properties of the system. The samples were characterized by rheological measurements. The structural isomerization of trans-to-cis for trans-OMCA occurred after UV light irradiation. The transformation of the system after UV light irradiation was determined by UV-vis absorption spectroscopy, rheological measurement and cryo-TEM observation. Surface tension measurements were carried out to investigate the role of trans-OMCA and UV light in C16mimBr aqueous solution. Critical aggregation concentration (cac), effectiveness of surface tension reduction (Πcac), maximum excess surface concentration (Γmax) and minimum area occupied per surfactant molecule (as) were investigated. Critical packing parameter was introduced to express the mechanism of aggregation behavior transition.

Investigation of micelle formation by N-(diethyleneglycol) perfluorooctane amide fluorocarbon surfactant as a foaming agent in aqueous solution

Micelles formed by nonionic fluorocarbon surfactant N-(diethyleneglycol) perfluorooctane amide as a foaming agent due to its excellent foaming performance in aqueous solution were studied through surface tension, dynamic light scattering, isothermal titration calorimetry, and dissipative particle dynamic simulation. The surface activity, adsorption, and thermodynamic parameters (ΔG0m, ΔG0ads, ΔH0m, ΔS0m, ΔHAm, ΔC0p,m) of micellization were systematically investigated. The experimental results showed that this nonionic fluorocarbon surfactant had superior surface activity and the micelle formation was entropy-driven. The micelle formation was also demonstrated by dynamic light scattering and isothermal titration calorimetry. Furthermore, to better understand the micelle formation, dissipative particle dynamic (DPD) simulation was conducted to simulate the whole formation process.

Experimental study of acrylamide monomer polymer gel for water plugging in low temperature and high salinity reservoir

ABSTRACT Water plugging agent has been widely applied on oilfield EOR processes for decades. Conventional plugging agents used on reservoirs with low temperature (50°C) and high salinity (28.6 × 104 mg/L) encounters with some limitations, such as slow gelling, weak gel strength, and poor instability. To overcome these problems, a novel acrylamide monomer polymer gel with strong gel strength, controllable gelling time and good stability was developed. The gelation processes of the plugging agent system at low temperature and high salinity is studied. The cross-linking reaction process of plugging agent is found to be in three stages: induction stage, rapid cross-linking, and stable stage. The composition of this plugging agent system is optimized: 5~7.5 wt% acrylamide + 0.5~0.75 wt% cross-linking agent + 0.005 ~0.12 wt% retarder + 0.5 wt% initiator. The plugging rate is over 96.5% in high permeability sandpack. It also displays good shear resistance. With the continuous flooding by water after the gel is formed, the polymer gel shows good flooding resistance. It can block the water effectively until 10 PV of injected water.

Novel investigation based on cationic modified starch with residual anionic polymer for enhanced oil recovery

ABSTRACT Cationic modified starch polymer (CMSP) is a newly developed green chemical agent designed to reutilize the residual anionic polymer found in reservoirs for enhanced oil recovery (EOR). In this study, a series of experiments were conducted to investigate the phase behavior of the residual anionic polymer, CMSP solution, and the flocculation generated from the mixture in plugging capacity and capability of enhancing oil recovery in heterogeneous reservoirs. The experiment results show that the phase behavior of the residual anionic polymer and CMSP solution could be divided into two parts: rapid flocculation reaction and dispersion reaction. The main mechanisms of the rapid flocculation reaction were charge neutralization and bridging. Based on the above results, an optimal amount of CMSP was chosen for plugging capacity, stability, and EOR study. Plugging tests in both parallel cores and EOR in three-layer heterogeneous square cores illustrate that the injected CMSP slug after polymer flooding can effectively block the high-permeability zone and initiate the remaining oil in middle- to low-permeability zones. The investigation results prove that the CMSP solution, injected after polymer flooding, reduces the pollution of produced fluid and further improves oil recovery. GRAPHICAL ABSTRACT