Intense
interest has been shown in the development of “smart
nanofluids” because they can dramatically change their flow
properties in complex fluid systems. We introduce a robust and straightforward
approach to develop a smart nanofluid system, in which associative
silica nanoparticles (ASNPs) were incorporated to regulate their flow
properties in rock pores. ASNPs were synthesized by covalently coating
a hydrophobically associative hygroscopic zwitterionic poly[2-methacryloyloxyethyl
phosphorylcholine (MPC)-co-divinylbenzene (DVB)]
shell layer on 20 nm sized silica nanoparticles (NPs) by surface-mediated
living radical polymerization. The essence of our approach is to copolymerize
DVB, which endows the polymer shell of ASNPs with a weak long-range
hydrophobic attraction. This leads to the favorable formation of a
wedge film as a result of structural disjoining pressure. This wedge
film made the oil adsorbed on the rock surface more dewettable, thus
enhancing the efficiency of oil recovery. As a result of this unique
behavior, the ASNP nanofluid developed in this study remarkably improved
the fluidity of complex oil fluids; ∼5 vol % oil recovery enhancement
and ∼0.3 psi pressure reduction were also achieved in comparison
to neat nanofluid controls.
This
study reports a Pickering emulsion flooding system, in which
the oil–water interface is structurally stabilized by a complex
colloidal layer consisting of silica nanoparticles, dodecyltrimethylammonium
bromide (DTAB), and poly(4-styrenesulfonic acid-co-maleic acid) sodium salt (PSS-co-MA). The colloidal
layer was generated by adsorption of PSS-co-MA on
the silica nanoparticles as a result of the van der Waals attraction
and by adsorption of DTAB onto the PSS-co-MA layer
as a result of the electrostatic attraction, thus providing the mechanically
robust, stable interface. To demonstrate a practical applicability
to the enhanced oil recovery, the complex colloidal dispersion fluid
was injected into the Berea sandstone for a core flooding experiment.
The result revealed that the colloidal dispersion significantly increased
the oil recovery by ∼4% compared to the case of flooding water.
This means that the emulsion drops in situ produced
in the core could readily flow through the rock pores. We attribute
this to the fact that the oil–water interface made with the
complex colloidal phase not only increased the structural stability
of the emulsion drops but also provided them deformability without
any drop breakup or coalescence.
Microbially enhanced oil recovery involves the use of microorganisms to extract oil remaining in reservoirs. Here, we report fabrication of microgel particles with immobilized Bacillus subtilis for application to microbially enhanced oil recovery. Using B. subtilis isolated from oil-contaminated soils in Myanmar, we evaluated the ability of this microbe to reduce the interfacial tension at the oil-water interface via production of biosurfactant molecules, eventually yielding excellent emulsification across a broad range of the medium pH and ionic strength. To safely deliver B. subtilis into a permeable porous medium, in this study, these bacteria were physically immobilized in a hydrogel mesh of microgel particles. In a core flooding experiment, in which the microgel particles were injected into a column packed with silica beads, we found that these particles significantly increased oil recovery in a concentration-dependent manner. This result shows that a mesh of microgel particles encapsulating biosurfactant-producing microorganisms holds promise for recovery of oil from porous media.
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