Nitrogen foam flooding is a promising technique for enhanced oil recovery, but instability of the foam limits its application. In this article, partially hydrophobic modified SiO 2 nanoparticles with an anionic surfactant, sodium dodecyl sulfate (SDS), were used together to increase foam stability. Micromodel flooding and sandpack flooding were adopted to assess the stability and effect on enhanced oil recovery of the SiO 2 stabilized foam (SiO 2 /SDS foam). The experimental data showed that the foam stability was decreased with an increase in temperature, while the foam volume was increased first and then decreased. SiO 2 /SDS foam showed better temperature tolerance than the SDS foam (foam stabilized by SDS) due to the adsorption of nanoparticles on the surface of the bubble. Almost all of the bubbles maintained spherical or ellipsoidal shape with prolonged time due to the enhanced surface dilational viscoelasticity, which was different from that of SDS foam. According to the micromodel flooding results, SiO 2 /SDS foam displaced more oil than brine flooding, SDS solution flooding, or SDS foam flooding. As the foam stability was enhanced, gas mobility and channeling were controlled effectively. In addition, more oil on the pore wall and in the dead-end pores was displaced out because of the higher viscoelasticity of the SiO 2 /SDS foam. The sandpack flooding results showed that the increase of differential pressure and profile control effect was a proportional function of the SiO 2 concentration in SiO 2 /SDS foam. The test with a higher SiO 2 concentration resulted in a higher oil recovery when SiO 2 concentration was less than 1.5 wt %.

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Transportation of water across nanochannels is of great importance for biological activities as well as for designing novel molecular devices/machines/sensors, which has wide applications in nanotechnology. With the development of experimental and computational facilities and technologies, it becomes possible to study the water dynamics inside and across the nanoscale channels by both experiments and numerical simulations. When the radius of a nanochannel is appropriate, the water molecules inside the channel form a single-file structure. Water confined in these nanoscale channels usually exhibits different dynamics not seen in the bulk system, including the wet–dry transition due to confinement, concerted hydrogen-bond orientations and flipping, concerted motion of water molecules and wavelike density distribution pattern. The permeation of water across the channels also shows unique behaviours, such as extra-high permeability, excellent on–off gating behaviour with response to the external mechanical and electrical signals and noises, reduction and enhancement by charge distributions on the channel walls, as well as directional transportation by a combination of charges close to a channel. In this review, we examine some of the recent advances in the dynamics of these single-file water molecules inside very narrow nanochannels.

The development of hydraulic fracturing has created a huge demand for fracturing fluids with high performance and low formation damage in recent years. In this paper, a foam stabilized by partially hydrophobic modified SiO 2 nanoparticles and sodium dodecyl benzenesulfonate (SDBS) was studied as a fracturing fluid. The properties of SiO 2 /SDBS foam such as rheology, proppant suspension, filtration, and core damage were investigated. The experimental data showed that the stability and thermal adaptability of sodium dodecyl benzenesulfonate (SDBS) foam increased when silica (SiO 2 ) nanoparticles were added. The surface tension of SDBS dispersion almost did not change after SiO 2 nanoparticles were added; however, the dilational viscoelasticity of the interface increased, indicating that the SiO 2 nanoparticles attached to the interface and formed a stronger viscoelasticity layer to resist the external disturbance. The proppant settling velocity in the SiO 2 /SDBS foam was found to be 2 orders of magnitude lower than that in a pure SDBS foam. The total leakoff coefficient of the SiO 2 /SDBS foam was found to be lower than that of an SDBS foam. Although the core damage ratio of the SiO 2 /SDBS foam was slightly larger than that of an SDBS foam, compared to GEL/SDBS, the core damage caused by the SiO 2 /SDBS foam remained at a low level. SiO 2 nanoparticle−surfactant-stabilized foam is superior to a surfactant-stabilized foam and causes lower core permeability damage than a gel−surfactant-stabilized foam. It is recommended for use in hydraulic fracturing, particularly for fracturing stimulation in tight and shale gas reservoirs.

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CO2 foam can control the CO2 mobility and improve the sweep efficiency in reservoirs; however, CO2 foam stabilized solely by surfactants is not stable. Nanoparticles can improve the performance of CO2 foam. The synergistic effect of SiO2 nanoparticles and sodium dodecyl sulfate (SDS) on the CO2 foam stability was studied in this paper. The experimental results show that the synergistic effect requires an SDS/SiO2 concentration ratio of 0.1–0.4. The strength of the effect increases as the SDS/SiO2 concentration ratio increases from 0.1 to 0.17 but then decreases as the ratio further increases from 0.17 to 0.4; thus, a ratio of 0.17 provides the best performance for CO2 foam. The mechanisms of the synergistic effect of SDS and SiO2 include modulating the position of nanoparticle adsorption on the CO2 and liquid interface, improving the interfacial properties of the CO2 foam, and reducing its liquid discharge and coarsening. SiO2 nanoparticles can also improve the CO2 foam performance under high temperatures and pressures. The visual flooding experiment reveals that the addition of SiO2 nanoparticles can improve the stability of CO2 foam in porous media and shows good tolerance of crude oil. SDS/SiO2 foam can increase the pressure differences of the flow in sandpacks after water flooding and improve the oil recoveries markedly. As the SDS/SiO2 concentration ratio increases, the pressure differences and enhanced oil recovery first increase and then decrease. The best CO2 foam flooding performance is achieved at an SDS/SiO2 concentration ratio of 0.17, which is related to the CO2 foam stability. The experimental results provide theoretical support for improving CO2 foam flooding under reservoir conditions.

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