CO2 Injection and Storage in Deep Saline Aquifers: Sensitivities on Model Gridding and Geochemistry

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. Thus, a synthetic model of a deep saline aquifer was set up and a large number of simulations were performed to investigate the impact of model gridding, CO2 injection strategy and parameters characterizing the system. Real data taken from the literature were used for the sensitivity analyses. The outcomes of the investigations were examined in terms of induced pressure variations, CO2 plume distribution and quantity of trapped CO2 according to the different trapping mechanisms. Results provided a very interesting and novel insight about the need for fine grids especially where the injection wells are located and for the definition of a suitable CO2 injection strategy. They also showed the need for a thorough characterization of the rock and formation water composition controlling the geochemical effects and for the rock-fluid interaction properties controlling the capillary trapping.