Daijun Du

Amphoteric hyperbranched polymers with multistimuli-responsive behavior in the application of polymer flooding

Amphoteric hyperbranched polymers (AMHPMs) that respond to shear rate, temperature, salt, and pH were synthesized using a water free radical polymerization technique. The Mw of this novel polymer is much lower than that of the conventional linear hydrophobically associative polymer (HAPAM). The hydrodynamic size could be effectively tuned by adjusting the terminal functional groups of the hyperbranched monomer. In the semidilute regime, multiple hydrodynamic subchains and effective intermolecular associations between neighboring branches of polymeric chains cooperatively govern the comprehensive characteristics of AMHPMs. Rheological measurements revealed the pseudodilatant behavior in the lower shear rate region, followed by the pseudoplastic behavior of AMHPMs. Moreover, the elasticity of AMHPM-2 played a dominant role and no Gc is observed within the experimental frequency. Static experiments convincingly proved that the multiple subchains provided AMHPMs with a wider temperature-, salt- and pH-responsive region in comparison to that for HAPAM. Most importantly, the reversible hydrodynamic characteristic scale due to the mutual transformation from association to disassociation, and the excellent anti-mechanical degradation for AMHPMs in the simulative porous medium, further verified that this unique type of hyperbranched polymer is promising for the application of polymer flooding for enhanced oil recovery (EOR).

Synthesis and characterization of hyperbranched associative polyacrylamide

Hydrophobically modified polyacrylamide with hyperbranched structure (HDPAM) was synthesized by water free-radical copolymerization based on functional hyperbranched polyamide-modified ultrafine silica as functional monomer and methacryloxyethyl-dimethyl cetyl ammonium bromide as hydrophobic monomer. The chemical and spatial network structure of HDPAM were investigated by means of FTIR, 1H NMR, TGA and SEM, respectively. The rheological measurements indicated that the HDPAM solution was viscoelastic fluid. With the increase of HDPAM concentration, both intermolecular association efficiency of hydrophobic groups and apparent viscosity of HDPAM solution increased. HDPAM solution had good thixotropy and temperature tolerance property. Moreover, compared with HPAM, HDPAM demonstrated superior properties on the aspects of viscosification property, temperature resistance and salt tolerance.

Synthesis and evaluation of β-cyclodextrin-functionalized hydrophobically associating polyacrylamide

Modified β-cyclodextrin and N-phenethyl-methacrylamide were utilized to react with acrylamide and acrylic acid to synthesize hydrophobically associating polyacrylamide (HMPAM) via photoinitiated free-radical micellar copolymerization. HMPAM was characterized using Fourier transform infrared (FT-IR) spectroscopy, 1H nuclear magnetic resonance (1H NMR), thermogravimetric analysis (TGA), scanning electron microscopy (SEM) and viscometry. Compared with partially hydrolyzed polyacrylamide (HPAM), HMPAM demonstrated superior properties on aspects of thickening ability, salt tolerance, temperature resistance and oil displacement efficiency. It was found that the apparent viscosity reached a maximum at 45 °C and the viscosity retention ratio reached 87.56% at 95 °C; at a certain range of salinity, HMPAM exhibited an evident salt-thickening phenomenon; the simulative enhanced oil recovery tests illustrated that HMPAM could remarkably enhance oil recovery by 16.4% while HPAM could enhance oil recovery by 10.8%. Moreover, the viscoelasticity and surfactant compatibility of HMPAM were investigated. The results indicated that HMPAM has potential application for enhanced oil recovery.

Application potential of in situ emulsion flooding in the high-temperature and high-salinity reservoir

Abstract In this research, an emulsifier formulation named SC-18 for W/O system was screened out and evaluated for feasible application of in-situ emulsion flooding in high-temperature and high-salinity reservoir. Results showed that SC-18 could reduce interfacial tension to 10–2 order of magnitude and change rock wettability from oil-wet to water-wet, which was beneficial to decrease residual oil saturation and improve displacement efficiency. Meanwhile, rheological testing showed that emulsion produced by SC-18 exhibited good temperature tolerance and mechanical stability, which favored mobility control and sweep efficiency enhancement under harsh conditions. In addition, good viscoelasticity of produced emulsions could also improve sweep efficiency by strengthening plugging and diverting effects of emulsion droplets, namely enhancing “Jiamin effects.” By means of natural core flooding and visualized plate model, it was proved that in-situ emulsion flooding with SC-18 could improve both displacement efficiency and sweep efficiency for high-temperature and high-salinity reservoir. GRAPHICAL ABSTRACT