A sandstone reservoir at a depth of 2800 m in a western India onshore field contains highly under saturated light oil of 470 API with viscosity of 0.2 cp. The reservoir has a permeability ranging 50 to 300 md and high temperature of around 130 Deg C. It is exploited by supplementing the partial water drive with water injection. Water injection was initiated in the early part of its producing life and has recovered more than 30% of OIIP. Meanwhile, availability of natural gas from deeper reservoirs in the field initiated a thinking process to examine the processes involving both miscible and immiscible displacement with gas injection to improve the recovery factor from the reservoir. The reservoir was not found suitable for miscible process due to higher miscibility pressure as compared to prevailing reservoir pressure of 250 Kg/cm2. Viability of immiscible WAG was ascertained through both laboratory investigations and numerical simulation prior to its testing on a pilot scale in the field. The process resulted in an increase in oil production along with reduction in water cut from the pilot and offset wells. Encouraging pilot results led to the decision of expanding the process to the entire field. The paper also evaluates the effects of different critical parameters on the recovery factor from immiscible WAG process through reservoir simulation studies.

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