Stability and rheological properties of HPAM/nanosilica suspensions: Impact of salinity

Abstract

The stability and rheological properties of HAPM/nanosilica suspensions in different saline environments including deionized water, NaCl brine and simulated formation water were investigated. The stability results indicated that the presence of cations in brine, especially divalent cations Mg2+ and Ca2+, was the main cause of instability of HPAM/nanosilica suspensions. The stability of suspensions decreased with the increase of nanosilica concentration. In deionized water, the HPAM/ nanosilica suspensions exhibited a greater viscosity than HPAM solution at low shear rates, while the opposite trend was evident at higher shear rates. Moreover, the temperature resistance and viscoelasticity of the suspensions were poorer. This was attributed to the formation of hydrogen bonding between nanosilica and HPAM in deionized water, as evinced by infrared spectroscopy. In NaCl brine and simulated formation water, the viscosity of HPAM solution increased and the viscoelasticity was enhanced by the addition of nanosilica. Infrared spectroscopy experiments showed that the hydrogen bonding between nanosilica and HPAM in brine was weaker than that in deionized water. The increase in viscosity of HPAM solution was attributed to the electrostatic interaction between cations in brine and nanosilica, which weakened the shielding effect of cations on the HPAM molecular, furthermore, the polymer chains could be adsorbed on the surface of the nanosilica to form a network structure of cationic bridges that increased the rheological properties of HPAM solution.