Enhanced Gas Recovery (EGR) is a way of producing residual gas in depleted gas reservoirs. CO2 injection is a promising method for EGR by increasing the reservoir pressure and also gas-gas displacement. The miscibility of injected CO2 and residual gas in place is an important factor in this process.

The objective of this work is to investigate the miscibility process of CO2 injection into gas reservoirs using a compositional and a black oil reservoir simulator. A synthetic simulation model is built for this process having injection and production wells. The effect of gas miscibility is studied for both simulators and the results are compared to find optimum miscibility parameters.

The simulation results show that compositional result is similar to the black oil run, when the miscibility factor in the later case is almost half of the complete miscible process. In case of no miscibility the extension front is very sharp while for the case of complete miscibility the CO2 front is more advanced toward production well with wider length of miscible zone.

The findings of this paper could be beneficial for further pilot and field case study for monitoring of the observation and abandonment wells. Also the method is helpful in using black oil simulator as an alternative, less working effort and same reliable for CO2 sequestration in comparison to a compositional simulator.

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