It
has been shown that nanofluids can significantly impact the
forces at both fluid–fluid and fluid–solid interfaces.
Nanofluids have also been reported in laboratory studies to enhance
oil recovery. However, mechanisms of oil recovery by nanofluids in
natural porous media are not well understood. More specifically, there
is an absence of direct and quantitative evidence of oil mobilization
by nanofluids at the pore level. In this study, we probe the mechanisms
through which nanofluids enhance pore-scale sweep efficiency during
oil displacements. We decouple the effects of nanofluids on interfacial
tension (IFT) and wettability by using a combination of silica nanoparticles
and a nonionic surfactant. We performed a set of miniature core-flooding
experiments integrated with a high-resolution imaging technique at
elevated pressure and temperature conditions to examine the effects
of nanofluids on oil recovery in Berea sandstone samples aged dynamically
with crude oil. The pore-scale displacement mechanisms were investigated
by directly measuring in situ contact angles in visualized images
of the pore space, mapping the distribution of remaining oil globules,
and examining the dynamic IFT data. The simple SiO
x
nanofluid had better performance in recovering oil from an
oil-wet sandstone sample compared with blank brine. Based on in situ
contact angle measurements, wettability reversal was identified as
the principal mechanism responsible for the observed behavior. The
complex SiO
x
nanofluid, which incorporated
a nonionic surfactant to lower IFT, generated the highest oil recovery
because of a synergistic effect between the wettability reversal and
IFT reduction mechanisms.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.