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.

No abstract

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 H NMR. The rheological properties of wormlike micellar system under different temperatures, pH conditions, and UV irradiation times are measured. As confirmed byH 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.

No abstract

Interests in using nanofluids for enhanced oil recovery (EOR) applications has been increasing. Herein, a novel surfactant-free water-based nanofluid for EOR was constructed using active silica nanoparticles. Active silica nanoparticles were synthesized via condensation of hexanedioic acid with the −OH group of silica. Water-based nanofluid was obtained by transforming carboxyl into carboxylate on the surface of active silica nanoparticles in water. The particle size of the active silica nanoparticles in water ranged from 10 to 20 nm. The interfacial activity of the nanoparticles was endowed through the shape change of the active silica nanoparticle surface groups to minimize their interface energy. The morphology and surface components of the active silica nanoparticles were characterized by transmission electron microscopy and Fourier transform infrared spectroscopy. The interfacial activity of the active silica nanoparticles was proved through interfacial tension and interfacial dilational modulus measurements. Active silica nanoparticles exhibited a stronger ability to reduce interfacial tension and enhance the interfacial film strength than silica nanoparticles. Contact angle measurements showed that this nanofluid exhibited excellent capabilities of oil displacement from a solid surface and wettability alteration. Spontaneous imbibition tests of ultralow permeability cores using different liquid phases (active silica nanofluid, silica nanofluid and brine) were conducted. Oil recovery using active silica nanofluid was higher than that of using silica nanofluid or brine. Active silica nanofluid at a low concentration could display an equal EOR efficiency with highly concentrated silica nanofluid. These results indicated the possible application of the proposed active silica water-based nanofluid in EOR. This preparation method could be used to prepare surfactant-free active nanofluids, and the surfactant-free active nanofluid shows great potential for EOR applications.