Scaling study of fluids displacement leads to proper understanding of pore-to-field scale flow mechanisms and correct evaluation of effectiveness of various recovery methods. Scaling study of immiscible forced gravity drainage, or gas assisted gravity drainage (GAGD), at laboratory scale and reservoir scale is considered here. Inspectional analysis (IA) is used to determine dimensionless scaling groups that characterize the fluid displacement and production mechanisms. It is found that scaling immiscible GAGD displacement in a homogeneous reservoir needs matching of five dimensionless scaling groups. For heterogeneous reservoirs, Dykstra-Parson coefficient which represents the permeability heterogeneity is also required. It is shown that none of the dimensionless groups can individually correlate the efficiency of the process. Hence, a new combined dimensionless group in reservoir scale which incorporates all the dominant forces is derived. The model is evaluated and verified by comparing its predictions with experimental results and extensive field simulations figures. The model is found reliable for fast oil recovery prediction of GAGD process after 2 pore volume injection in homogeneous and heterogeneous reservoirs and proposing their optimal production plan.