Mohsen Montazeri - M.S. Student of Petroleum Engineering, Science and Research Branch of Azad University and Commissioning and Operation of Oil Industry OICO , Tehran, Iran
Saeid Sadeghnejad - Assistant Professor, Department of Petroleum Engineering, Faculty of Chemical Engineering, Tarbiat Modares University, Tehran, Iran

Gas injection into carbonate formations is one of the most important activities to protect oil reserves that can guarantee a steady production .On-time injection of enough gas can result in the recovery of billions barrels of oil. In addition, it can preserve a huge amount of gas for the next generations. If the reservoir depth is shallow, or the reservoir fluid has a little amount of intermediate components, the flooding of rich gases is highly recommended. In the designing of a miscible injection process, firstly the minimum miscibility pressure should be measured or determined analytically. In this study, first the PVTi software is implemented to evaluate the miscibility of different injected gas, including carbon dioxide, nitrogen, methane, and different proportion of hydrocarbon gases. Subsequently, E-300 software is used to predict the recovery of the gas injection into the formation under study from one of the Iranian carbonate onshore fields. The investigation of the optimum injection rate as well as finding the proper layer of injection is investigated in details. The results show that the CO2 flooding after a long natural production period result in higher efficiency than the miscible injection of methane at the early stage of production.

Gas Injection Rate, Miscible, Immiscible, Recovery, Optimum Flooding Scenario