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As the important role of enhanced oil recovery (EOR) in meeting the world’s energy requirement is growing, use of nanoparticles in lieu of, or in combination with, the existing EOR agents to expand EOR’s applicable range is receiving significant attention. Two of the most actively investigated applications are: 1) wettability alteration by addition of nanoparticles into the waterflood injection water, and 2) use of nanoparticle-stabilized Pickering foams and emulsions mainly for EOR process mobility control. As comprehensive reviews are recently available on these topics, two other emerging nanoparticle applications are critically reviewed here: 1) nanoparticle addition for enhanced polymer flooding, and 2) use of magnetic nanoparticles for oil displacement control. Three and five proposed mechanisms of these two applications are critically reviewed, respectively. The most recent progresses are covered, and the challenges and possible future works are discussed.

Liquid imbibition, the capillary-pressure-drivenflow of a liquidinto a gas, provides a mechanism for studying the effects of solid–liquidand solid–liquid–gas interfaces on nanoscale transport.Deviations from the classic Washburn equation for imbibition are generallyobserved for nanoscale imbibition, but the identification of the originof these irregularities in terms of transport variables varies greatlyamong investigators. We present an experimental method and correspondingimage and data analysis scheme that enable the determination of independenteffective values of nanoscale capillary pressure, liquid viscosity,and interfacial gas partitioning coefficients, all critical transportvariables, from imbibition within nanochannels. Experiments documentedherein are performed within two-dimensional siliceous nanochannelsof varying size and as small as 30 nm × 60 nm in cross section.The wetting fluid used is the organic solvent isopropanol and thenonwetting fluid is air, but investigations are not limited to thesefluids. Optical data of dynamic flow are rare in geometries that arenanoscale in two dimensions due to the limited resolution of opticalmicroscopy. We are able to capture tracer-free liquid imbibition withreflected differential interference contrast microscopy. Results withisopropanol show a significant departure from bulk transport valuesin the nanochannels: reduced capillary pressures, increased liquidviscosity, and nonconstant interfacial mass-transfer coefficients.The findings equate to the nucleation of structured, quasi-crystallineboundary layers consistently ∼10–25 nm in extent. Thislength is far thicker than the boundary layer range prescribed bylong-range intermolecular force interactions. Slower but linear imbibitionin some experimental cases suggests that structured boundary layersmay inhibit viscous drag at confinement walls for critical nanochanneldimensions. Probing the effects of nanoconfinement on the definitionsof capillary pressure, viscosity, and interfacial mass transfer iscritical in determining and improving the functionality and fluidtransport efficacy of geological, biological, and synthetic nanoporousmedia and materials. [ABSTRACT FROM AUTHOR]