Study and Evaluation of WAG and Comparison with Water and Gas Injection in One of the Fractured Oil Reservoirs in the West of Iran

By development and improvement of oil industry, the tendency to increase the production of oil fields has been paid more attention. The growing need to increase the output and ultimate recovery by enhanced oil recovery (EOR) methods has received great significance as far as mature oil fields are concerned. Water Alternating Gas (WAG) injection also is one of these methods. WAG is defined as the injection of both water and gas into the same reservoir. WAG injection is an oil recovery method initially aimed to improve sweep during gas injection mainly by using water to increase the contact surface of injected fluid with the reservoir; it is also to control the mobility of the displacement and create stable mobility front. This including definition covers MWAG (miscible), IWAG (immiscible), HWAG (hybrid), SWAG (simultaneous), SSWAG (selective simultaneous). In this study, the various scenarios of WAG injection have been simulated in one of the reservoirs of National Iranian Oil Company by the GeoQuest commercial software package and ECLIPSE100 module; the efficiency coefficient, total oil production in factors effective on injection such as injection cycle, injection type and injection method (IWAG, HWAG, SWAG and SSWAG) are studied and compared. Then, the scenarios of water, gas, and WAG injection are studied and compared to choose the appropriate method of injection in the interested field. At last, by designing various scenarios of water, gas, and WAG injection in four- and five-spot injection patterns, the efficiency, residual oil saturation, and total oil production are studied and compared in various methods in the above patterns in order to find the optimal and appropriate pattern of injection. The results show that by choosing suitable parameters, the efficiency and production of WAG method will be higher than water and gas injection.