Evaluation of oil recovery by water alternating gas (WAG) injection oil-wet and water-wet systems

Water alternating gas injection (WAG) is normally employed to improve the volumetric sweep efficiency of miscible flooding processes. Literature search indicated a number of numerical studies investigated the effect of flooding rate, gravity forces, slug size, and heterogeneity on WAG processes performance. However there are very few numerical and experimental studies conducted on the effect of wettability on the efficiency of WAG processes. This work examines how to optimize WAG processes for carbon dioxide (CO₂) floods above the minimum miscibility pressure (MMP) in both oil-wet and water-wet reservoirs. Stream tube simulation was used to assess the effects of WAG ratio, system wettability, flood pattern, solvent injection rate, project timing, and reservoir heterogeneity on the sweep efficiency and overall all recovery efficiency for oil-wet and water wet reservoirs. A series of secondary miscible carbon dioxide WAG displacement runs were performed employing WAG ratio's of 1:1, 2:1, 1:2, 3:1, 1:3 and straight carbon dioxide. The main conclusions of this research show that system wettability has a significant impact on the optimization of WAG ratio, solvent injection rate, project timing, and flooding pattern selection.