The influence of salinity on the viscous instability in viscous-modified low-interfacial tension flow during surfactant-polymer flooding in heavy oil reservoirs

► Ultimate oil recovery decreases by increasing the salinity of injectant. ► Dynamic cluster-growth nature of the front is the main cause of viscous instability. ► Decrease in salinity delays the onset of instability. ► During early stages, wavelength of viscous fingers increases by increasing salinity. ► By neglecting the viscous instability, pore-scale capillary number is overestimated.