Geological carbon dioxide sequestration and underground storage offers a promising solution to reduce greenhouse gases in the atmosphere. However, technical feasibility and safety issues must be duly addressed. 3D numerical models of potential underground storages to perform compositional simulations of the system dynamic behavior are a way to study the storage of carbon dioxide in existing deep geological formations. After a brief literature review on the CO2 trapping mechanisms when CO2 is injected in deep saline aquifers and on current CCS projects, the thesis focuses on how to set up representative models and obtain reliable simulation results. The task requires the definition of a large set of parameters describing the fluid and the rock properties as well as the rock-fluid interaction properties, but also consideration on how to perform the simulations.