This paper reports the results of extensive experimental and numerical studies of the effects of well-defined heterogeneous oil-wet porous media (lenses) on simultaneous first contact miscible water alternating gas (FCMWAG) displacements. Flow displacement and effluent profiles have been obtained from well-characterized laboratory experiments in two-dimensional heterogeneous beadpacks. The effects of WAG ratios have been examined. All experiments were then modeled using IMPES finite difference simulator without using history matching (all simulations used directly measured porous media properties as inputs) to quantify the accuracy of the simulation when modeling the FCMWAG displacements in a porous media with lenses heterogeneity. Results revealed that neglecting lenses heterogeneity will cause incorrect reservoir engineering interpretation; for example that of core floods for absolute permeability, relative permeability and residual oil saturation determinations.