The aim of this project was to study the leakage of CO2 in a Geological Carbon Sequestration (GCS) system. To define the GCS system, a tool that is known as an FEP database was used. FEPs are the features, processes and events that develop scenarios for the goal of the study. Combinations of these FEPs can produce thousands of scenarios. However, among all of these scenarios, some are more important than others for leakage. The FEPs that were used as scenario developers were the formation of the liquid flow, the salinity of the formation liquid, diffusion as a process for gas bubble transport and the depth of the reservoir layer. In this study, the leakage path is considered as the presence of a fracture in sealed caprock. The fractures can be modeled using various approaches. Here, I represented the influence of fracture modeling by applying the Equivalent Continuum Method (ECM) and the Dual-Porosity and Multi-continuum methods to leakage. This study suggests that considering groundwater in the aquifer would reduce the leakage of CO2 and that a shallower formation leads to higher leakage. This study can be expanded to future studies by including external FEPs that are related to the FEPs that were used in this study.