Adding chemical additives with in-situ generation of foam is an approach to enhance SAGD (steam assisted gravity drainage) performance both in terms of oil production and SOR (steam-oil ratio). Simulation studies tell that, owing to gas mobility control, interfacial tension reduction and emulsification, a steam chamber profile is substantially controlled with reduced heat loss and residual oil saturation drops significantly. Strong foam accumulates along the inner boundary of a steam chamber owing to lower capillary pressure and higher nitrogen concentration. A heterogeneous model based on an Athabasca project is employed to show that bubbles are conducive to improve volumetric sweep by diverting steam into a low permeable area. Simultaneously, foam favors to reduce the influences of a top water zone and maintain bowl-shaped and uniformly-developed steam chamber growth.