A gas injection for the purpose of pressure maintenance was initiated in a field located in south of Iran in 1984. It is the largest gas injection project in Iran and possibly in the world without the use of compressors. The field was discovered in 1968. It consists of two non-communicating formations one on top of the other namely Asmari and Bangastan group. The Asmari reservoir contains oil and the Bangastan reservoir contains dry gas with little amount of condensate at much higher pressure. Gas is produced from one well completed in Bangastan reservoir and injected into an injection well completed in Asmari reservoir by a direct pipeline.

History matching was performed over 18 years of production of the Asmari field. Long term prediction of the reservoir performance was obtained for 42 years above the initial 18 years of history matching. Prediction was evaluated under different scenarios namely: 1) natural depletion, 2) pressure maintenance, and 3) repressurizing the reservoir close to its initial pressure.

This paper will present the actual reservoir data for both formations over eighteen years of their operation. In addition, history matching and future performance of the reservoir predicted by a simple simulator based on material balance concept will be presented. It is encouraging to observe a satisfactory match of the reservoir performance and to gam insight into its future performance without resorting to a much more sophisticated and much more expensive simulators.

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