This work aims to improve the rheological properties of partially hydrolysed polyacrylamide (HPAM) for enhanced oil recovery by using SiO 2 nanoparticles (NPs).Novel aqueous HAPM based SiO 2 nanocomposites were formulated and their rheological properties were investigated under different salinities, temperature and aging time. The results show that the inclusion of silica NPs improved significantly the viscosity and viscoelastic properties of HPAM especially under high temperature and high salinities. The NP/HPAM hybrid showed an impressive thermal stability at T= 80 ºCafter 12 days, and the viscosity reached ~5 times of that HPAM at 0.8w% NP loading. The FT-IR spectra data confirmed that the formation of hydrogen bond between the carbonyl groups in HPAM and the silanol functionalities on the surface of silica NPs, which attributed to the improved performance. The oscillation test indicated that seeding SiO 2 remarkably facilitated the cross links among polymer molecules and made the hybrids more elastically dominant. For a given HPAM concentration, it was observed that there was acritical NP concentration (CNC)which many indicating the absorption status of SiO 2 NPsonto HPAM, and the salinity also affected the viscosity value.

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High temperature and high salinity (HTHS), and extreme pH conditions can significantly affect the stability of polymers and deteriorate the performance of polymer in enhancing oil recovery (EOR). This work advances polymer flooding in harsh environment on two fronts: engineering polymers with improved temperature tolerance, and dispersing suitable nanoparticles in the synthesised polymers to further improve their capabilities in withstanding temperature, salinity, and different pH conditions. Different modified acrylamide copolymers (polymer synthesized from two different monomers) and ter-polymers (polymer synthesized from three different monomers) are produced via free-radical polymerization and multi wall carbon nanotubes (MWCNTs) were introduced to obtain aqueous polymer dispersions with unique properties.The conversion, molecular weight and poly dispersity of co/ter-polymers were evaluated by 1 H-NMR, and GPC analysis. The interfacial, rheological behaviour and stability of the dispersions was investigated under HTHS conditions at various pH values to identify the suitable candidates for EOR applications. The oil recovery performance is examined in a core flooding set-up under 85 o C and American Petroleum Institute (API) brine conditions. The polyampholytic ter-polymer and polyelectrolyte copolymer containing negative sulfonate group showed improved viscosity and stability in the presence of MWCNTs in an alkaline and salinity conditions respectively. Comparing to pure polymer dispersions, the addition of MWCNTs to polymer improves oil recovery efficiency at high temperature (85 °C) in the presence of both alkaline pH and API brine conditions, yet with lower pressure drop. This, shows great promise for future EOR applications.

Graphical abstract2 ABSTRACT A novel one-pot method was developed in this work to synthesize and disperse nanoparticles in a binary base fluid. As an example, stable magnetite iron oxide (Fe3O4) dispersions, i.e., nanofluids, were produced in a high ionic media of binary lithium bromide-water using a microemulsion-mediated method. The effects of temperature and precursor concentration on morphology and size distribution of produced nanoparticles were evaluated. An effective steric repulsion force was provided by the surface functionalization of nanoparticles during the phase transfer, supported by the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The formed nanoparticles exhibited a superior stability against agglomeration in the presence of high concentrations of lithium bromide, i.e., from 20 to 50 wt.%, which make them good candidates for a range of novel applications.

Hydrolyzed polyacrylamide (HPAM) is a polymer that extensively used in chemical industry and hydrocarbon extraction and refinery processes, but suffers a common problem of high‐temperature instability. This study improved high‐temperature rheological characteristics of HPAM by using novel graphene oxide (GO) nanosheets. Stable GO dispersions in aqueous HPAM were formulated, and their dynamic and viscoelastic behaviors were studied. The results showed that the addition of GO significantly increased the viscosities and high‐temperature stability of the base polymer fluid, as well as the elastic properties of the dispersion. Spectral data indicated the formation of covalent linkages and electrostatic hydrogen bonding between the GO and the HPAM functional groups, leading to enhanced stability and viscosity that is beneficial for high‐temperature oil recovery. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47582.

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