Hairong Wu

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.

A New Water Displacement Curve for the High Water-cut Stage

Field practices show the adaptability of the water displacement curve at the ultra-high water-cut stage is poor. The authors first proposed a new water displacement curve, and then put forward a new method to obtain the parameters in the new curve equation. Then a new characterization equation to describe the relationship between water-oil relative permeability ratio and water saturation is proposed, which is the new water displacement curves theoretical basis. Finally, based on the case study it is proved that the new curve are more accurate in predicting the development performance at the ultra-high water-cut stage.

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.

Stability mechanism of O/W Pickering emulsions stabilized with regenerated cellulose

The stability and mechanism of O/W Pickering emulsions stabilized with regenerated cellulose were investigated. The Turbiscan Lab Expert Stabilizer, Particle Size Analyser, and Physica MCR301 Rheometer were used. When the concentration of regenerated cellulose increases, the aggregation of regenerated cellulose, emulsion stability and bulk and interfacial viscoelasticity increase as the diameter of the oil droplets decreases. In addition, the emulsions display a typical gel-like characteristic, and the oil-water interfacial shear rheological behaviour slightly differs from that of the O/W Pickering emulsions. This difference can be attributed to the aggregation of regenerated cellulose in the droplet surface under the shear condition. The emulsions exhibit excellent salt resistance at high salt concentrations. Moreover, the regenerated cellulose displays a better temperature resistance than amphiphilic polymer (AP), which is commonly used in oilfields. Hence, commercially available regenerated cellulose can be used as an ideal candidate for enhanced oil recovery.

Study on the relationship between emulsion stability and droplet dynamics of a spontaneous emulsion for chemical enhanced oil recovery

ABSTRACT Spontaneous emulsion (SE) has attracted increasing attention, especially in the development of low-permeability reservoirs (with an average throat radius of 0.1–2 µm) for enhanced oil recovery. In this work, based on multiple light scattering principles, the relationship between emulsion stability and the droplet dynamics of SEs was investigated. The results showed that the synergistic effect of surfactant and polymer was crucial for oil emulsification in brine, since the stability of the emulsion was greatly improved. The emulsion stability and droplet dynamics depend on the temperature, concentration, and type of emulsifier. The optimal combination system had the lowest Turbiscan stability index value, and the emulsion stability time was more than 2000s. The average droplet size was 1.50 µm, and the droplet migration rate was 7.21 mm/h. The stability of the emulsion was resulted from the microscopic droplet dynamics. By reducing the migration rate of the droplets, stability of the emulsion can be obtained. Finally, the stability and droplet dynamics mechanism of the system were explained by using a schematic representation of the various equilibriums in the spontaneous emulsification flooding system. GRAPHICAL ABSTRACT

The optimum synergistic effect of amphiphilic polymers and the stabilization mechanism of a crude oil emulsion

ABSTRACT The amphiphilic polymers (APs) possess both thickening and emulsifying properties that were optimized by the combination of different APs. The properties and synergistic mechanisms of the combination system, consisting of HAP-L and HAP-S, were studied and optimized according to their proportion at various concentrations, temperatures, salinities, and shear rates. Furthermore, various methods were applied to study the emulsification properties of the combination system. The results show that the viscosity, salt resistance, temperature resistance, and shear resistance of the combination system are greatly improved. It is noteworthy that the combined system displays the optimized properties when the mass ratio of HAP-S and HAP-L is 3:2. Under that circumstance, the emulsions also turn to be more stable and display more uniform particle distribution. After combination, more hydrophobic groups participate in the intermolecular association, and the structure of the network is enhanced. Therefore, a combination of various APs can be used as an effective approach to improve the viscosity and emulsification capability of APs for oil recovery.

Ultra-Low Interfacial Tension of a Surfactant under a Wide Range of Temperature and Salinity Conditions for Chemical Enhanced Oil Recovery

Abstract Ultra-low interfacial tension (IFT) is an important parameter for selecting surfactants to apply in chemical enhanced oil recovery (CEOR). In this study, the IFT between the solution of the surfactant ANSM and Dagang crude oil was measured using the spinning drop method. The effects of the surfactant concentration, temperature, salt types and aging time on the IFT were investigated in detail. The results showed that ANSM effectively reduced the IFT without alkali. Ultra-low IFT was formed in a wide range of surfactant concentrations from 0.05∼ 0.5 wt.% and a wide range of temperatures from 20∼80°C. In addition, ANSM also showed great NaCl tolerance, with a maximum NaCl concentration of 130000 mg · L−1. Furthermore, 0.1 wt.% ANSM maintained an ultra-low IFT, even with 900 mg · L−1 CaCl2 or 1300 mg · L−1 MgCl2, in the presence of 10000 mg · L−1 NaCl. ANSM also had an excellent stability; the solution maintained the ultra-low IFT for 60 days at 90°C. Thus, ANSM proved itself as a potential candidate for CEOR.

Application of α-amylase as a novel biodemulsifier for destabilizing amphiphilic polymer-flooding produced liquid treatment

The performance and de-emulsification mechanism of α-amylase, a novel environmental friendly biodemulsifier in petroleum industry, was investigated at room temperature. The effects of α-amylase on the viscosity of amphiphilic polymer solution and de-emulsification rate were studied by changing the concentration of α-amylase, temperature and salinity. Polymer molecular weight, Zeta potential, interfacial film strength and interfacial tension were measured to investigate the de-emulsification mechanism of α-amylase. The results show that α-amylase is an efficient biodemulsifier to increase the de-emulsification rate of amphiphilic polymer emulsions. Hydrolysis of α-amylase to amphiphilic polymers destroys the structure of the amphiphilic polymer, thereby reduces the viscosity and the interfacial film strength of the system. Once de-emulsification is completed, the lower layer, i.e. the emulsified layer, will be clear. Thus, α-amylase can be applied as an effective de-emulsifier for amphiphilic polymer-stabilized O/W emulsion.