This study provides an overview for the carbon dioxide sequestration process in an oil reservoir by using the software CMG's GEM. Different scenarios are applied for the oil reservoir description. Firstly, a single layered reservoir is considered and simulation studies are performed, as this reservoir is homogeneous, heterogeneous and fractured. Secondly, a multi-layered reservoir is examined. In the second case, a heterogeneous system and a heterogeneous system composed of homogenous layers are selected. For these two arguments, it is assumed that injection perforation is in the bottom layer and production perforation is in the top layer. As a third argument of multi-layered reservoir, a heterogeneous system composed of homogenous layers is selected and it is assumed that all layers are perforated for both injection and production. Finally, the effects of those properties on CO2 injection capacity, cumulative oil and gas production are discussed. In the single layered reservoir cases, cumulative oil production and CO2 injection capacity increase by reason of heterogeneity. When the system is fractured, cumulative production, CO2 injection and storage capacity decrease due to rapid increase in pressure as a consequence of low porosity. For the multi-layered reservoir, the case of homogeneous layers with two perforation intervals produces higher hydrocarbon recovery, amount of CO2 injection and storage. When CO2 is injected to all layers, pressure increases more rapidly, resulting in abridged time of injection. Hence, cumulative oil and gas production and mass of CO2 injected are restricted.