A Simplified Model to Predict Heterogeneity Effects on WAG Flooding Performance

A steady-state, analytical model is presented to estimate ultimate recovery from water-miscible gas floods in heterogeneous reservoirs. The model is used to investigate miscible flooding performance as a function of well spacing, rock-fluid properties, and reservoir description. Results show that layers or streaks of relatively high vertical permeability within an otherwise homogeneous formation cause little change in overall recovery. Flooding performance, however, is generally improved by low permeability heterogeneities, depending on their relative vertical position. Discontinuous shales near the bottom or the middle of the reservoir enhance vertical sweep efficiency, while such shales near the top have much less effect on oil recovery.