Salt effect on hydrophobically modified polyacrylamide-containing crude oil emulsions: stability and rheology study

The emulsification of amphiphilic polymer is inevitably affected by the salinity environment in the preparation and flooding process. The variation of emulsions in stability and rheology has a significant influence on the efficiency of polymer flooding. Thus, the effect of NaCl and CaCl2 on the emulsification behavior of hydrophobically modified polyacrylamide (HMPAM) was investigated. A novel dynamic multiple light scattering method was proposed to analyze the variation of emulsion stability. Then, the emulsions with addition of salt were systematically researched in terms of oil droplet size, polymer adsorption, and rheology properties. With the increase of NaCl concentration, the emulsion stability with 1500 mg L−1 HMPAM (above the critical aggregation concentration) decreases monotonically; with the increase of CaCl2 concentration, the emulsion stability rises at first then decreases. It is found that the structural viscosity of the polymer solution is the dominant factor in stabilizing the crude oil emulsion. Modulation effect of the salt ions on the emulsion stability is achieved by regulating the aggregate structure in the aqueous solution. Oscillation-shear-oscillation rheological experiments were conducted to investigate the rheological properties of emulsions. The results show that the viscoelasticity of emulsion system at high salt concentration decreases after high-rate shearing and the recovery of the viscoelasticity is slowed down due to the inhibition of hydrophobic association. This study provides theoretical guidance for elucidating the regulation rules and mechanism of salts on the amphiphilic polymer-containing crude oil emulsions.