A novel nanofluid based on fluorescent carbon nanoparticles for enhanced oil recovery (EOR) was developed. Fluorescent carbon nanoparticles prepared by a simple and rapid method were used as a chemical agent for EOR and fluorescence imaging. Transmission electron microscope and Fourier transform infrared spectrometer were employed to observe the shape, size, and surface components of the fluorescent carbon nanoparticles. The fluorescent carbon nanoparticles could be instantly dispersed in water without any auxiliary equipment. The nanofluid showed excellent antitemperature, antisalinity, oil displacement, and wettability alteration properties. The nanofluid (0.1 wt %) could reduce the oil–water interfacial tension to 13.4 mN/m. The oil recovery of a core immersed in nanofluid was significantly improved. The core intersection was observed by a fluorescence microscope. The fluorescence image demonstrated that the fluorescent carbon nanoparticles had seeped into the core. The fluorescent carbon nanoparticle-based nanofluid provides a promising and efficient chemical agent for EOR.

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.

A new kind of self-dispersing silica nanoparticle was prepared and used to enhance oil recovery in spontaneous imbibition tests of low-permeability cores. To avoid the aggregation of silica nanoparticles, a new kind of silica nanoparticle was prepared through the surface modification with vinyltriethoxysilane and 2-mercaptobenzimidazole as modified agents. Transmission electron microscopy, Fourier transform infrared spectroscopy, dynamic light scattering, and ζ potential measurements were employed to characterize the modified silica nanoparticles. Dispersing experiments indicated that modified silica nanoparticles had superior dispersity and stability in alkaline water. To evaluate the performance of silica nanofluids for enhanced oil recovery compared to pH 10 alkaline water and 5 wt % NaCl solution, spontaneous imbibition tests in sandstone cores were conducted. The results indicated that silica nanofluids can evidently improve oil recovery. To investigate the mechanism of nanoparticles for enhanced oil recovery, the contact angle and interfacial tension were measured. The results showed that the adsorption of silica nanoparticles can change the surface wettability from oil-wet to water-wet and silica nanoparticles showed a little influence on oil/water interfacial tension. In addition, the change of the oil droplet shape on the hydrophobic surface was monitored through dynamic contact angle measurement. It was shown that silica nanoparticles can gradually detach the oil droplet from the hydrophobic surface, which is consistent with the structural disjoining pressure mechanism.

Understanding and controlling water or ion transport in nanochannels plays an important role in further unravelling the transport mechanism of biological membrane channels and designing functional nanofluidic devices. Molecular dynamics simulations were conducted to investigate water and ion transport in graphene nanochannels. Similar to electron coulomb blockade phenomenon observed in quantum dots, we discovered an ionic coulomb blockade phenomenon in our graphene nanochannels, and another two ion transport modes were also proposed to rationalize the observed phenomena under different electric-field intensities. Furthermore, on the basis of this blockade phenomenon we found that the Open and Closed states of the graphene nanochannels for water transport could be switched according to external electric-field intensities, and electroosmotic flow could further enhance the water transport. These findings might have potential applications in designing and fabricating controllable valves in lab-on-chip nanodevices.

Foam regeneration, an important step in foam profile control and foam flooding, is determined by the process of large dispersed mother bubbles breaking into small ones. The bubble behaviors in 3-D pore-throat microchannels were investigated in different polymer solutions by a high-speed digital camera. The initial bubble slug was generated through a co-flowing geometry and then flowed through a microfluidic constriction. Both breakup and non-breakup were observed at the operating conditions of Ca ranging from 0.000068 to 0.0067, and the breakup mechanisms can be divided into two different types: single bubble snap-off and multi-bubbles pinch-off. Emphases are given to the influences of pore-throat structures, capillary number and continuous phase viscoelasticity on the size variation of the daughter bubbles. The average daughter bubble size decreases with the increase of the pore-throat ratio or elasticity of solution. Furthermore, the change of the average size of daughter bubbles with capillary number could be scaled with a power law in breakup type Ι, while in breakup type ΙΙ, the mother bubble size becomes another decisive factor.Download high-res image (125KB)Download full-size image

The adsorption and viscoelastic properties of a micellar solution of 2-hydroxyl-propanediyl-1,3-bis(hexadecyldimethylammonium bromide), abbreviated as 16-3OH-16, have been investigated by surface tension and rheological measurements. Meanwhile, an aqueous solution of propanediyl-1,3-bis(hexadecyldimethylammonium bromide), abbreviated as 16-3-16, was also examined. From the steady state and oscillatory rheological results, a notable difference in shear viscosities between the two systems was observed. Zeta potentials and size distributions confirm the change in the potentials and hydrodynamic diameters, and these results are in good agreement with the rheological results. The differences of the two solutions were attributed to the effect of the hydroxyl group on the spacer of 16-3OH-16. Molecular dynamic simulations and density functional theory (DFT) calculations were performed to investigate the non-covalent interactions in the solution and the difference between the molecular orbitals and the electrostatic potentials. Our research shows that a more uniform distribution of positive charges around the spacer could result in a more effective electrostatic screening effect between the charged headgroups, and promote the formation of a worm-like micelle. Also, hyperconjugation becomes stronger when the hydroxyl group is introduced on the spacer of the gemini molecule.

Bubble behaviors in the single and cascaded three-dimensional (3-D) pore-throat micromodels were studied at the operating ranging from 0.0007 to 0.0249. It was found that the average size of daughter bubbles decreased with the rising of the pore-throat ratio, length of throat and mother bubble velocity. The variation of the average size of daughter bubbles with capillary number could be scaled with a power law. In addition, the bubble breakup mainly occurred in the first pore-throat structure and the size of the daughter bubbles maintained almost stable.Download high-res image (214KB)Download full-size image

ABSTRACTPolymer gel, as a water plugging treatment agent, has been successfully used in enhanced oil recovery (EOR) of mature oil fields. A new thermal-resistance and salt-tolerance polymer gel was developed based on HPAM and HQ/HMTA under the condition of high-temperature (100.8 °C) and high-salinity (up to 19.8 × 104 mg/L and Ca2+&Mg2+ 0.8 × 104 mg/L). The influence factors of gelling performance and coreflood performances were studied, the microstructure of the gel was observed with the environmental scanning electron microscopy, and gelation mechanism was proposed to illuminate the detailed gelation process. The gelation time decreases and the gel strength increases with the increase of polymer concentration, crosslinker concentration, or temperature. Although shearing had a negative effect on the viscosity of gelling solution, the gel strength, and the stability of gel have not been affected. The gelling solution has a good ability of injection and could selectively flow into high permeable zone. Additionally, the plugging rate increases and stays above 85% with the increase of the permeability or the gel strength. The microstructure of the gel confirms that the gel formed a three-dimensional network structure. Based on the microstructure and the reaction process of the gel, a possible gelation mechanism is proposed. This study suggests that the gel system can be used in harsh reservoir conditions and the gelation time and gel strength can be controlled with adjusting the formation rate and the concentration of crosslinking agents. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2016, 133, 44359.

The current study aims at in-depth profile control to further improve oil recovery by studying the matching relationship between the size of dispersed particle gel (DPG) and geometry of reservoir pore-throat. The DPG products with different sizes were prepared, and their microscopic characteristics and particle size distributions were analyzed. The matching factor, which was defined as the ratio of average size of DPG particles to mean size of pore-throats, was introduced to represent the matching relationship. The injection properties and plugging capacities were systematically studied by a series of core flooding experiments to optimize the matching factor. The matching factor was optimized from 0.21 to 0.29 depending on both the injection pressure and the plugging rate. In addition, the results of multi-point pressure measurement experiment verified that the DPG particles exhibited good in-depth migration and plugging ability within the optimized matching factor values. Meanwhile, scanning electron microscope (SEM) was used to study the distribution of DPG particles in porous media. The results intuitively showed that the DPG particles can migrate to the deep of porous media and induce effective plugging to the pore-throats. Moreover, the enhanced oil recovery experiments for different matching factors were conducted, and the mechanisms for enhanced oil recovery by DPG with different matching factors were proposed. The enhanced oil recovery with an optimized matching factor was much higher than that with a smaller or larger matching factor. Owing to good in-depth migration and plugging ability of DPG particles with optimal matching factors, the subsequent injected water was diverted into low permeability zones with high oil saturation and, consequently, widely swept the remaining oil in low permeability zones.

The formation of self-assemblies in mixed amino acid-based anionic N-hexadecanoylglutamic acid (HGA) and cationic benzyldimethyl hexadecylammonium chloride (HDBAC) surfactants in aqueous solutions has been characterized. With rheological analysis, the viscoelastic properties of the mixed system are found to be completely dependent on the concentration of HDBAC. Molecular dynamics simulation results suggest that the morphology of self-assembly can be regulated from spherical micelles to wormlike micelles by the addition of HDBAC. The aromatic group of HDBAC adsorption provides a “charge-neutral” function to the micelle corona; the repulsive interactions within the head group of HGA are progressively screened and closely packed. In addition, the dynamic processes and formation mechanisms of self-assembly were analyzed in detail with molecular simulation techniques.

To achieve in-depth profile control and further improve oil recovery, a new profile control agent, termed a dispersed particle gel (DPG), has been developed and reported. In this paper, the DPG particles with sizes ranging from submicrometer to micrometer are prepared successfully from phenol–formaldehyde cross-linked polymer gel by the high speed shearing method. The preparation method is convenient and easy to scale up for the field application. The microscopic characteristics of the DPG have been investigated by transmission electron microscopy (TEM) and dynamic light scattering (DLS). Parallel sandpack tests and microscopic visualization tests have been conducted to gain insights into the profile control mechanism. Additionally, scanning electron microscope (SEM) has been used to study the distribution of DPG particles in porous media. The results show that the DPG particles can block the high permeability layers by accumulating in large pore spaces or by directly plugging small pore throats. Meanwhile, the viscoelastic DPG particles can achieve in-depth profile control due to the elastic deformation and migration into the porous media of the reservoir. Moreover, the oil displacement tests show that the DPG can increase the sweep efficiency and effectively enhance oil recovery.

•A simple class of photo-responsive system was systematically studied.•Rheological study shows photo-induced transition from wormlike to rodlike micelles.•The microstructure of the photo-responsive system was analyzed by cryo-TEM.•The photo-responsive mechanism was proposed, stating the detailed process clearly.In this work, we report a simple class of photo-responsive system that consists of cationic surfactant, N-methyl-N-cetylpyrrolidinium bromide (C16MPB), and the photoresponsive organic derivative, trans-ortho-methoxycinnamic acid (trans-OMCA). The system is studied by UV spectra, cryo-transmission electron microscopy, and rheological measurements. C16MPB and trans-OMCA in basic aqueous solution can self-assemble to form viscoelastic wormlike micelles. Upon exposure to UV light, OMCA undergoes a photoisomerization from trans to cis, which results in a change of the geometry of the C16MPB–OMCA complexes. The wormlike micelles can transform into spherical or rodlike micelles. We hope this study may enrich the understanding of photo-responsive wormlike micelles composed by cationic surfactants and photo-sensitive additives in water.

•A bio-based surfactant regenerated from waste cooking oil was synthesized.•The interfacial tensions can reach up to an ultralow level (< 10− 2 mN·m− 1).•The thermodynamic parameters of micellization were systematically investigated.•This bio-based surfactant exhibits great potential oilfield application in EOR.To regenerate the non-edible waste cooking oil and significantly reduce the negative effect on human being and the environment, a bio-based nonionic-anionic amphoteric sulfonate type surfactant with excellent interfacial and surface properties was synthesized. The interfacial tensions between crude oil and water can reach up to an ultralow value as 0.0040 mN·m− 1 without additives. With dynamic light scattering and surface tension, micelles formed by N-aliphatic amide-N,N-diethoxypropylsulfonate bio-based surfactant were studied. This work also systematically investigated the surface activity, adsorption behavior, and thermodynamic parameters (ΔGm0, ΔGads0, ΔHm0, ΔSm0, ΔHmA, ΔCp,m0) of micellization. According to the experimental results, it can be seen that the bio-based surfactant has an excellent surface activity, besides, the micelle formation is entropy and enthalpy co-driven at 25–45 °C. Dynamic light scattering also illustrated the micelle formation. Through this research work, we expect to gain some insights into the phase behaviors of this bio-based surfactant and broaden its great potential oilfield application in enhanced oil recovery.

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.

Venezuela heavy oil under various hydrogen pressures has been hydrocracked to investigate the variation of asphaltene components during reaction. Asphaltenes have been isolated from the product and analyzed by X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, and nuclear magnetic resonance (NMR). The experimental data revealed that the interlamellar spacing and interchain spacing of the asphaltenes increased while the layer diameter decreased with the hydrogen pressure increasing. At the same time, the amount of aromatic carbon and alkyl carbon of the asphaltenes decreased gradually and the amount of naphthenic carbon increased. As the hydrogen pressure increased, the substitution ratio and the condensation degree parameter (HAU/CA) of the aromatic system in the periphery increased gradually and the replacement index and peri-position condensation index of asphaltenes decreased obviously.

•Silica nanoparticles were found to reduce surfactant adsorption effectively.•EOR test proved a 4.68% growth of oil recovery by the injection of SNP - surfactant solution.•The mechanism of the inhibition using SNP was proposed.This paper aims at making a thorough investigation on surfactant adsorption on rock under the influence of silica nanoparticles (SNP). The results showed that SNP can reduce surfactant adsorption effectively. With SNP concentration of 0.1, 0.2 and 0.3 wt%, static adsorption experiments showed that sodium dodecyl sulfate (SDS) adsorption can be significantly reduced to 2.57, 2.12, and 1.73 from 2.84 mg/g, and the dynamic adsorption of SDS decreased to 0.92, 0.77, and 0.66 from 1.16 mg/g, respectively. Our subsequent tests conformed a 4.68% growth of oil recovery by the injection of SNP - surfactant solution compared to the normal surfactant solution. The mechanism of the enhanced oil recovery is assumed to be the inhibition of surfactant adsorption and the profile control capability of silica nanoparticles. This study proves the SNP - surfactant flooding is a cost-effective way for enhanced oil recovery.

Through extensive experiments, a reusable viscoelastic surfactant (rVES) fracturing fluid using a self-designed and synthesized surfactant was developed. Laboratory performance evaluation results showed that various performances of rVES fracturing fluid are excellent. The most attractive aspect is the gelling and gel breaking of rVES fracturing fluid was achieved by altering the pH value. The recycled fracturing fluid still maintains good performances through three times cycles, which represents that it has good prospects for re-use of flowback waters. In addition, large-scale coarse-grained molecular dynamics (CGMD) simulations results clearly revealed the formation mechanism of rVES fracturing fluid at the molecular level.Download full-size image

Aiming at water shut-off in high temperature reservoirs, the hydroquinone (HQ)–hexamethylenetetramine (HMTA) gel system was studied. The gelation performance and effects of various parameters were systematically evaluated. With increase of the concentrations and temperature, gelation time decreases and gel strength increases. In addition, gelation rate and gel strength were enhanced on adding acid. Moreover, the gel system shows good salt tolerance. The thermal stability measurement indicates that the gel can maintain stability up to 140 °C. Uniformly distributed three-dimensional network structure was formed in the gel. At last, the gelation mechanism was proposed, illuminating the detailed gelation process clearly.The microstructure of the gel was analyzed by the environmental scanning electron microscopy (ESEM). From the ESEM micrographs, uniformly distributed three-dimensional network structure is observed. Polymer chain bunches with thickness of several micrometers to tens of micrometers, connecting with a node, surround the pores forming a three-dimensional network structure. In the structure, the amide groups (CONH2) from the polymer crosslink with the hydroxyl groups (CH2OH) from the cross-linkers, which contributes to the uniformly porous mesh-like network structure. The uniformly porous network structure is conducive to perfect water holding capacity, which contributes to low water separating proportion and good stability of the gel system.Download full-size image

The adsorption and viscoelastic properties of a micellar solution of 2-hydroxyl-propanediyl-1,3-bis(hexadecyldimethylammonium bromide), abbreviated as 16-3OH-16, have been investigated by surface tension and rheological measurements. Meanwhile, an aqueous solution of propanediyl-1,3-bis(hexadecyldimethylammonium bromide), abbreviated as 16-3-16, was also examined. From the steady state and oscillatory rheological results, a notable difference in shear viscosities between the two systems was observed. Zeta potentials and size distributions confirm the change in the potentials and hydrodynamic diameters, and these results are in good agreement with the rheological results. The differences of the two solutions were attributed to the effect of the hydroxyl group on the spacer of 16-3OH-16. Molecular dynamic simulations and density functional theory (DFT) calculations were performed to investigate the non-covalent interactions in the solution and the difference between the molecular orbitals and the electrostatic potentials. Our research shows that a more uniform distribution of positive charges around the spacer could result in a more effective electrostatic screening effect between the charged headgroups, and promote the formation of a worm-like micelle. Also, hyperconjugation becomes stronger when the hydroxyl group is introduced on the spacer of the gemini molecule.