the performance evaluation of viscous-modified surfactant water flooding in heavy oil reservoirs at varying salinity of injected polymer-contained surfactant solution

this study examines the effects of change in the concentrations of monovalent and divalent ions in the polymer-contained surfactant solution on the macroscopic behavior of viscous-modified surfactant waterflooding in heavy oil reservoirs. salts that are used in this set of floods were sodium chloride, magnesium chloride, and calcium chloride. the results indicate that four different ranges of salinity (in terms of cacl2 concentration) exist. each of these ranges renders a unique behavior regarding the ultimate oil recovery trends. there exists a range of salinity in which the ultimate oil recovery does not change with the salinity increase. the second salinity range is beyond the salt tolerance (i.e., first salinity range) of the polymer-contained surfactant solution, which results in a decrease in the ultimate oil recovery. in the third range of salinity, ultimate oil recovery is enhanced due to the plugging of high-permeable pores. in the fourth salinity range, precipitation increases as the salinity increases and more pore throats (even some pores with intermediate permeability) are plugged and, thus, the ultimate oil recovery decreases.