Steam Assisted Gravity Drainage (SAGD) is one of the most widely used in-situ thermal recovery methods for bitumen production in Alberta, Canada. In the present work, we investigate the effect of water mobility inside a reservoir on SAGD performance. In particular, the components of heat transfers (i.e. conduction and convection) ahead of a steam chamber are analyzed and formulated by considering steam condensate flow. We develop an unsteady state semi-analytical 2D SAGD model which couples convective and conductive heat transfer mechanisms with multiphase flows. The developed model is capable of predicting steam chamber expansion, oil and water production rates, and also distributions of temperature, fluid saturation and fluid mobility ahead of steam chamber. The result examination illustrates that the convection mechanism enhances heat transfer only in the vicinity of steam chamber edge while maximum oil mobility oil happens a few meters beyond the steam interface.