Study of a high salt tolerant amphiphilic polymer and its salt thickening mechanism

Abstract

Polymer flooding is the most reliable method for the petroleum industry to further enhance oil recovery from the developed oil field and to keep the total oil production. For the reservoirs with high salinity, traditional polymer fluids, for example partially hydrolyzed polyacrylamide (HPAM), are failed to improve oil recovery rate due to the molecular agglomeration caused by compression-diffusion electric double layer. By optimizing the copolymerization of cyclic structure monomer n-vinylpyrrolidone (NVP) and long-chain hydrophobic monomer cetyl dimethyl allyl ammonium chloride (C16DMAAC), a high salt tolerant amphiphilic polymer P(AM/NVP/C16DMAAC), abbreviated as PANC, is synthesized. The optimal polymerization conditions were determined depending on the apparent viscosity measured by the rheometer. The microstructure of the polymer was evaluated using Fourier transform infrared spectroscopy, nuclear magnetic resonance spectroscopy and scanning electron microscopy. The viscosity of 2000 mg/L PANC increased to 42.7 mPa·s at the salinity of 11.6 × 104 mg/L and temperature of 40 °C, while the viscosity of HPAM was only 7.3 mPa·s under the same condition. The viscosity of PANC was 479 % higher than that of HPAM, indicating the remarkable salt tolerant property of PANC. The viscosity of PANC increased from 12 mPa·s to 42.7 mPa·s when the salinity increased from 1 × 104 mg/L to 11.6 × 104 mg/L. By comparing the salt resistance of polymer PANC and polymer P(AM/AA/C16), abbreviated as AP-C16, indicating that NVP enhanced the rigidity of the PANC molecular chain, and hindered the shrinkage and curling of the molecular chain after salt addition. The inclusion effect of β-cyclodextrin on the hydrophobic groups of PANC indicated that PANC increased viscosity through the hydrophobic association of C16DMAAC. Furthermore, PANC showed a salt thickening ability due to the synergy effect of C16DMAAC and NVP. As such, the salt tolerant amphiphilic polymer PANC offers a novel polymer flooding material for oil displacement, especially under a high-salinity condition.