Fluid-fluid
interfacial reactions in porous materials are pertinent
to many engineering applications such as fuel cells, catalyst design,
subsurface energy recovery (enhanced oil recovery), and CO2 storage. They have been identified to control physicochemical properties
such as interfacial rheology, multiphase flow, and reaction kinetics.
In recent years, engineered waterflooding has been identified as an
effective way to increase hydrocarbon recovery and solid-fluid interaction
has been assessed as the key mechanism. However, in this study, we
demonstrated that in the absence of solid-fluid interactions (in strong
hydrophilic porous media), fluid-fluid interfacial reactions can significantly
affect multiphase flow and thus lead to an increased hydrocarbon recovery
during engineered carbonated waterflooding. We designed a microwaterflooding
system to evaluate the interfacial reactions during two phase flow
with engineered carbonated waters. Given that salinity controls the
amount of dissolved CO2, we injected carbonated high salinity
water and carbonated low salinity water to achieve different fluid-fluid
reactions. We injected the carbonated water in a sandstone with 99.5%
quartz under X-ray microcomputed tomography (μCT) scanning at
a resolution of 3.43 μm per pixel. Image processing shows that
carbonated low salinity waterflooding can recover 8% more oil than
carbonated high salinity waterflooding, while the quartz-rich sandstone
remains strongly hydrophilic in both samples. A gradual CT intensity
distribution indicates an interfacial phase generation between carbonated
brine and crude oil during carbonated waterflooding. Therefore, we
attributed the additional hydrocarbon recoveries to the fluid-fluid
interfacial reactions. To understand the effects of fluid-fluid reactions
on interfacial properties, we performed molecular dynamics simulations
to investigate the chemical species distribution at the interface,
interfacial tension (IFT) changes, and CO2 diffusion. The
MD simulation results revealed a layered structure of the interface,
a lower CO2 diffusion coefficient in carbonated high salinity
water, a lower IFT in carbonated low salinity water, a swelling hydrocarbon
phase in carbonated low salinity water, and more CO2 accumulated
at the interface between the hydrocarbon phase and carbonated low
salinity water. This work provides a general and fundamental understanding
of the influence of fluid-fluid interactions on the interfacial properties
between carbonated water and the hydrocarbon interface.