Gas reservoirs can be classified into dry gas reservoirs, wet gas reservoirs and Gas condensate reservoirs. In gas condensate reservoirs, the reservoir temperature lies between the critical temperature and the cricondentherm. The gas will drop out liquid by retrograde condensation in the reservoir, when the pressure falls below the dew point. This heavy part of the gas has found many application in industry and also in daily life and by remaining in reservoir not only this valuable liquid is lost but also its accumulation will result in forming a condensate bank near the well bore region which makes a considerable reduction in well productivity .
In this paper, gas injection has been studied in a gas condensate reservoir to increase the recovery factor moreover the capability of different injection gases (CO2, N2, CH4 and separator gas) has been compared through different injection schemes. The injection schemes considered were: different injection rates, different injection pressures and different injection durations .The results obtained showed that the response of the reservoir in different cases was different but that injection of all of them can increase the condensate recovery from 5% (in the least efficient case, i.e. in a very low injection pressure and with a very low injection rate) to 30 %. As many parameters can affect the decision of selecting the injection scheme, other than the gas and condensate recovery factor, doing an economical evaluation is inevitable to take them all into account and determine the optimum one.