Stability, rheology and displacement performance of nano-SiO₂/HPAM/NaCl dispersion systems

The stability, rheological properties and oil/water interfacial tension of Nano-SiO₂/HPAM/NaCl systems at 60 ℃ were studied by Zetasizer, rheometer and spin-drop method, respectively. The results indicated that the zeta potential value of nano-SiO₂ became more negative and the particle size was significantly increased with addition of HPAM. Meanwhile, there was no obvious turbidity phenomenon after 10 d. The nano-SiO₂/HPAM suspensions had higher viscosity and the viscosity retention was improved in the presence of salt at high temperature and shear rate as compared to HPAM solution. In this work, the nano-SiO₂ threshold for 0.18%(mass ratio) HPAM solution was 0.5% (mass ratio). When the mass ratio of nano-SiO₂ was less than 0.5%, the viscosity, storage modulus, loss modulus and creeping recovery properties were enhanced as well as the critical strain was decreased with the increase of nano-SiO₂ mass fraction. However, the opposite phenomenon was investigated when the mass ratio of nano-SiO₂ was more than 0.5%. The reason for this result was that the polymer amounts, polymer conformation onto the nano-SiO₂ surface and the network structure between nano-SiO₂ and HPAM were different when the nano-SiO₂ mass fraction was different. Oil/water interfacial tension values of nano-SiO₂/HPAM suspensions were lower than that of HPAM solution, and thus with addition of 0.2% and 0.5% (mass ratio) nano-SiO₂, the nano-SiO₂/HPAM suspensions had ultimate oil recoveries of 4.5% and 6.0% higher than polymer flooding.