Screening different water alternating carbon dioxide injection scenarios to achieve to the highest macroscopic sweep efficiency in a non fractured carbonate reservoir

Miscible gas flooding using carbon dioxide provides us excellent microscopic displacement efficiency in different mature oil fields. Due to the limitation of CO2, optimization of CO2-EOR process to reach to the best macroscopic sweep efficiency is an essential problem. Unfavorable mobility ratio and gravity segregation lead to viscose fingering and gravity override. Hence, areal and vertical sweep efficiencies decrease due to the early breakthrough of the injected gas. Different approaches are applied to change the injection scenario of the gas to control the mobility ratio and gravity effects. A comprehensive approach is needed to select the best scenario and optimize it to achieve the highest recovery in an economical manner. Different scenarios of water alternating carbon dioxide injection such as TWACO2 (Tapered Water Alternating CO2), WACO2 (Water Alternating CO2), SSWACO2 (Selective Simultaneous Water and CO2), and SWACO2 (Simultaneous Water and CO2) can be selected as candidates for the EOR operation. In this work, these scenarios were simulated and studied for a non-fractured reservoir. The simulation outcomes were coupled by an economical model and compared to the pure water and CO2 injection to specify the appropriate and optimized injection method to gain to the highest Net Present Value. Hence, by this method, the necessary amount of the injected gas and water were also optimized for the best scenario. By our simulations, we found that SWACO2 injection increased the total recovery compared to the primary recovery by 25.4 percent which was the highest. The achieved NPV was lower for this method compared to TWACO2. Hence, we recommended TWACO2 as the best method and we optimized it for application in the field.