In the common methods of water and gas injection, high and unsuitable mobility ratio within the injected fluid and the oil in the reservoir, leads to viscose fingering and reduction of sweep efficiency. It was originally intended to improve sweep efficiency during gas flooding, with alternating slugs of water and gas (WAG injection) designed by and large to follow the same route through the reservoir.

WAG injection has been widely applied since the late 1950s. The typical improved oil recovery (IOR) potential for WAG injection when compared with water injection is quoted in the literature at 5-10%. In this method, injection of water slugs followed by gas, leads to triple region, increase the contact level of injected fluid and reservoir, stable the movement front, and finally increase the recovery. However, depend on the conditions, type and pattern of injection, improvement of recovery is variable and different. WAG injection in five methods, immiscible, miscible, hybrid, simultaneous and selective simultaneous.

In this work, scenarios of WAG injection such as Immiscible WAG (IWAG), Hybrid WAG (HWAG), Simultaneous WAG (SWAG) and Selective Simultaneous WAG (SSWAG) and water and gas injection are compared to specify the appropriate injection method. Then ultimate oil recovery, residual oil saturation, daily and total oil production are compared in these scenarios. Also these scenarios in four and five spot injection patterns were compared.

Results indicated that, SSWAG injection has the higher oil production and lowest residual oil saturation. In addition, among these scenarios, SSWAG in 4-spot pattern had the highest recovery and daily oil production. 4-spot pattern had the higher recovery and lower residual oil saturation than 5-spot pattern, so adding the number of wells could not raise the recovery.

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