Wanli Kang

Surface rheological behavior of gelatin/ionic liquid-type imidazolium gemini surfactant mixed systems

The surface properties of gelatin solutions without and with ionic liquid-type imidazolium gemini surfactants have been investigated via surface shear and dilational rheology as well as surface tension measurements. Both the surface shear and dilational rheological properties show that the strength of gelatin film is enhanced in the presence of 0.005 mmol L−1[C12-4-C12im]Br2, and the storage modulus is larger than loss modulus for gelatin/[C12-4-C12im]Br2, indicating that gelatin/[C12-4-C12im]Br2 is an elastic film. With increasing the concentration of imidazolium gemini surfactant, the dilational modulus increases firstly and then passes through a maximum value, due to the electrostatic and hydrophobic interactions between surfactant molecules and gelatin chains. Although the surface tension of gelatin/surfactant mixed solution is identical to that of the pure surfactant solution at high surfactant concentration, the dilational modulus suggests that the surfactant molecules are unable to fully replace gelatin molecules from the air/water surface. The structure of the gemini surfactant has great effect on the surface viscoelastic modulus of gelatin, it is found that the gelatin film in the presence of imidazolium gemini surfactant with longer hydrophobic chain or longer spacer reveals the larger strength.

Mechanism and Influencing Factors on the Initial Particle Size and Swelling Capability of Viscoelastic Microspheres

Viscoelastic microspheres are spherical particles with a three-dimensional network structure and have obvious swelling capability. The initial particle size and swelling ratio were introduced to study the effect of preparation conditions and external environmental factors systematically. The initial particle size could be controlled by adjusting the preparation conditions. The swelling capability was affected by both preparation condition and external environmental factor. The mechanisms of swelling are formation of hydrogen-bonded hydrolysis and diffusion induced by osmotic pressure. This work can provide some references for the particle size adjustment of viscoelastic microspheres in the profile control and flooding of heterogeneous reservoirs. GRAPHICAL ABSTRACT

Study on the stabilization mechanism of crude oil emulsion with an amphiphilic polymer using the β-cyclodextrin inclusion method

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.

Influence of Water Content and Temperature on Stability of W/O Crude Oil Emulsion

Water content of W/O crude oil emulsion and temperature have great influence on stability of the W/O crude oil emulsion and the subsequent demulsification process especially for oil-water treatment centers using a two-step sedimentation demulsification process in Jilin oilfield. Electrical microscope and Turbiscan stability analyzer were employed to investigate the influence of water content and temperature on stability of synthetic W/O emulsion. The results show that the average water droplets size decreases when water content decreases, the emulsion stability decreases when water content or holding temperature increases, and the emulsion stability constant and the temperature have a linear relationship.

Synthesis, Aggregation Behavior and Emulsification Characteristic of a Multi-sticker Amphiphilic Polymer

A multi-sticker amphiphilic polymer P(AM-NaA-DCHAM) was synthesized using micellar polymerization. Fluorescent spectroscopy, rheology and SEM were used to characterize the aggregation behavior of P(AM-NaA-DCHAM) solutions. Above CAC, aggregation formed by intermolecular association of hydrophobic groups can induce large quantities of hydrophobic microdomains and strong elastic polymer gel network structures in P(AM-NaA-DCHAM) solutions. O/W crude oil emulsions stabilized by P(AM-NaA-DCHAM) were prepared, and a laser particle size analyzer and Turbiscan lab stability analyzer were employed to study their stability. O/W crude oil emulsions stabilized by P(AM-NaA-DCHAM) get more stable as polymer concentration increases. The stability mechanism of O/W crude oil emulsions stabilized by P(AM-NaA-DCHAM) is probably because the elastic polymer gel structure of P(AM-NaA-DCHAM) in the continuous phase has the ability to hold oil droplets.

CO2-triggered gelation for mobility control and channeling blocking during CO2 flooding processes

CO2 flooding is regarded as an important method for enhanced oil recovery (EOR) and greenhouse gas control. However, the heterogeneity prevalently distributed in reservoirs inhibits the performance of this technology. The sweep efficiency can be significantly reduced especially in the presence of “thief zones”. Hence, gas channeling blocking and mobility control are important technical issues for the success of CO2 injection. Normally, crosslinked gels have the potential to block gas channels, but the gelation time control poses challenges to this method. In this study, a new method for selectively blocking CO2 channeling is proposed, which is based on a type of CO2-sensitive gel system (modified polyacrylamide-methenamine-resorcinol gel system) to form gel in situ. A CO2-sensitive gel system is when gelation or solidification will be triggered by CO2 in the reservoir to block gas channels. The CO2-sensitivity of the gel system was demonstrated in parallel bottle tests of gel in N2 and CO2 atmospheres. Sand pack flow experiments were conducted to investigate the shutoff capacity of the gel system under different conditions. The injectivity of the gel system was studied via viscosity measurements. The results indicate that this gel system was sensitive to CO2 and had good performance of channeling blocking in porous media. Advantageous viscosity-temperature characteristics were achieved in this work. The effectiveness for EOR in heterogeneous formations based on this gel system was demonstrated using displacement tests conducted in double sand packs. The experimental results can provide guidelines for the deployment of the CO2-sensitive gel system for field applications.

The rheological characteristics for the mixtures of cationic surfactant and anionic–nonionic surfactants: the role of ethylene oxide moieties

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.

Stability, rheological property and oil-displacement mechanism of a dispersed low-elastic microsphere system for enhanced oil recovery

A dispersed low-elastic microsphere system, consisting of low-viscoelastic microspheres and polymers, is a novel suspension system for enhanced oil recovery in heterogeneous reservoirs. In this study, experiments were performed to characterize the morphology, viscoelasticity, and swelling performance of the synthetic low-elastic microspheres. The stability and rheological property of the dispersed low-elastic microsphere system was investigated using a Turbiscan Lab Expert stability analyzer and an MCR301 rheometer. In the flow and displacement experiments, the parallel-sandpacks model and microscopic visualization models were used to study the oil-displacement effect and micromigration mechanism of the low-elastic microspheres. The experimental results showed that the storage modulus (G′) of the synthetic low-elastic microspheres was only 23.6 Pa and they also had a good swelling property in the simulated formation water. The parallel-sandpacks test and micromodel test indicated that the dispersed low-elastic microsphere system was a promising agent for both conformance control and improved oil recovery in heterogeneous reservoirs. Moreover, the low-elastic microspheres had good deformation and shear resistance performances. Five transport behaviors, such as deformable passing through, partition passing through, blockage, adhesion, and directly passing through, of low-elastic microspheres in a porous medium have been put forward. This study not only provides an understanding of the properties of the dispersed low-elastic microsphere system but also supplies theoretical support for the mechanism of improving oil recovery for the dispersed low-elastic microsphere system.

Formation and phase transition of hydrogel in a zwitterionic/anionic surfactant system

The phase behavior and microstructure in a mixture of the zwitterionic surfactant N-hexadecyl-N,N-dimethyl-3-ammonio-1-propane sulfonate (HDPS) and anionic surfactant sodium dodecylsulfate (SDS) were studied. Analysis of its macroscopic appearance, tube inversion testing and rheological measurements were employed to characterize its phase behavior, and it was found that a hydrogel formed in an appropriate total concentration (CT) and molar percentage of SDS (XSDS) at 25 °C for HDPS/SDS systems. Microstructures in the hydrogel were identified to be long wormlike micelles and small spherical vesicles, using transmission electron microscopy (TEM). The coexistence of wormlike micelles and small vesicles brings an appropriate packing parameter (p), which indicates that the wormlike micelles reached a sufficient length and degree of entanglement to form the three-dimensional elastic hydrogel. The HDPS/SDS hydrogel transforms into a viscoelastic sol upon increasing the temperature, and the determined gel–sol transition temperature (Tg–s) has been determined to be around 30 °C, using optical and rheological methods. Besides, adding salt causes the wormlike micelles to lengthen and the rheological properties of the solution to change, such that it may even induce a sol–gel phase transition in the mixed zwitterionic and anionic surfactant system.

Research on association between multi-sticker amphiphilic polymer and water-soluble β-cyclodextrin polymer

The host cyclodextrin polymer-P(AM/A-β-CD/NaA) is prepared by redox free-radical copolymerization. Additionally, the multi-sticker amphiphilic polymer-P(AM/BHAM/NaA) as a guest polymer is synthesized using micellar polymerization. The copolymer structures are characterized by 1H NMR. Subsequently, all the polymers and inclusion complexes are evaluated in terms of apparent viscosity, optical absorption spectra and rheological property. The results indicate that the inclusion association between the cyclodextrin group (CD) and multi-sticker hydrophobic monomer (BHAM) is in accordance with ternary interaction (CD/BHAM = 2:1). Because of the inclusion association between the host and guest polymers, the solution of inclusion complex has much higher viscoelasticity even under the low amphiphilic polymer concentration. When the molar ratio of CD to BHAM is 1:1, the critical aggregation concentration (CAC) of the inclusion complex solution still remains. Furthermore, above the CAC, two types of associations, inclusion association and inter-molecular hydrophobic association, can occur in the complex solution and these interactions were also verified by fluorescence spectroscopy and atomic force microscopy (AFM). In this paper, the inclusion rule of cyclodextrin polymer with the multi-sticker amphiphilic polymer is discussed, and the rule of the enhanced solution viscosity is further explored.