Injection of colloids and suspensions in natural reservoirs with particle capture results in well injectivity decline. However, some initial improvement in injectivity was observed during waterflooding of oilfields and explained by increasing mobility of two-phase fluid during the displacement of more viscous oil by water. We derive an analytical model for axi-symmetric two-phase flow with simultaneous deep bed filtration of injected particles, formation of external filter cake, and its stabilization due to particle dislodgement. The explicit formula for dimensionless pressure drawdown (impedance) yields the type curve for impedance history. It is shown that the initial injectivity increase, induced by varying two-phase mobility, adds three degrees of freedom to one-phase impedance growth model. This additional information is used for tuning the models with the Corey relative permeability and the pseudo-relative permeability under the viscous-dominant displacement. Treatment of the data from three synthetic cases results in good agreement with the initial data, validating the developed model adjustment method. Three field case data have been considered. Good agreement between the field and modeling data along with common values of the obtained constants validate the developed analytical model for injectivity decline during waterflooding and its adjustment method.