| dc.description.abstract | To satisfy energy demands, the natural gas supply must be smoothed. This aim can be accomplished by means of underground natural gas storage. They provide large-scale seasonal storage of natural gas. To maintain reservoir pressure, and reduce the amount of unrecoverable natural gas, a cushion gas can be utilized. It is not economically feasible to use the working gas as a base gas because it cannot be extracted during the production stage. CO2 can be an effective substitute that has the additional environmental advantage of sequestering carbon. However, using a cushion gas can lead to subsurface mixing which can in turn impacts the purity of produced gas. The mixing phenomenon can be a challenge to the implementation of CO2 as base gas. This thesis aims to study the effect of some factors on the mixing phenomenon and the purity of the produced gas with the use of simulation tools. According to the results, well shut-in days at the beginning of the operation and prior to any production can improve the purity of the produced gas and delay the evaluation of the mixing zone. The production rate has a long-term effect on the operation and it should assess over different periods to set an optimum rate. Conforming to the results, it is possible to inject a huge amount of CO2 as a cushion gas without significantly affecting the purity of produced gas. | |